democritus atomic theory experiment

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Democritus, known in antiquity as the ‘laughing philosopher’ because of his emphasis on the value of ‘cheerfulness,’ was one of the two founders of ancient atomist theory. He elaborated a system originated by his teacher Leucippus into a materialist account of the natural world. The atomists held that there are smallest indivisible bodies from which everything else is composed, and that these move about in an infinite void. Of the ancient materialist accounts of the natural world which did not rely on some kind of teleology or purpose to account for the apparent order and regularity found in the world, atomism was the most influential. Even its chief critic, Aristotle, praised Democritus for arguing from sound considerations appropriate to natural philosophy.

1. Life and Works

2. atomist doctrine, 3. theory of perception, 4. the soul and the nature of living things, 5. theory of knowledge, 6. indivisibility and mathematics, 8. anthropology, other internet resources, related entries.

According to ancient reports, Democritus was born about 460 BCE (thus, he was a younger contemporary of Socrates) and was a citizen of Abdera, although some reports mention Miletus. As well as his associate or teacher Leucippus, Democritus is said to have known Anaxagoras, and to have been forty years younger than the latter (DK 68A1). A number of anecdotes concern his life, but their authenticity is uncertain.

The work of Democritus has survived only in secondhand reports, sometimes unreliable or conflicting: the reasoning behind the positions taken often needs to be reconstructed. Much of the best evidence is that reported by Aristotle, who regarded him as an important rival in natural philosophy. Aristotle wrote a monograph on Democritus, of which only a few passages quoted in other sources have survived. Democritus seems to have taken over and systematized the views of Leucippus, of whom little is known. Although it is possible to distinguish some contributions as those of Leucippus, the overwhelming majority of reports refer either to both figures, or to Democritus alone; the developed atomist system is often regarded as essentially Democritus’.

Diogenes Laertius lists a large number of works by Democritus on many fields, including ethics, physics, mathematics, music and cosmology. Two works, the Great World System and the Little World System (see the entry on doxography of ancient philosophy ), are sometimes ascribed to Democritus, although Theophrastus reports that the former is by Leucippus (DK 68A33). There is more uncertainty concerning the authenticity of the reports of Democritus’ ethical sayings. Two collections of sayings are recorded in the fifth-century anthology of Stobaeus, one ascribed to Democritus and another ascribed to an otherwise unknown philosopher ‘Democrates’. DK accepts both as relating to Democritus, but the authenticity of sayings in both collections is a matter of scholarly discussion, as is the relationship between Democritus’ atomism and his ethics.

Ancient sources describe atomism as one of a number of attempts by early Greek natural philosophers to respond to the challenge offered by Parmenides. Despite occasional challenges (Osborne 2004), this is how its motivation is generally interpreted by scholars today. Although the exact interpretation of Parmenides is disputed, he was taken to have argued that change is merely illusory because of some absurdities inherent in the idea of ‘what is not’. In response, Leucippus and Democritus, along with other Presocratic pluralists such as Empedocles and Anaxagoras, developed systems that clarified how change does not require that something should come to be from nothing. These responses to Parmenides suppose that there are multiple unchanging material principles, which persist and merely rearrange themselves to form the changing world of appearances. In the atomist version, these unchanging material principles are indivisible particles, the atoms. The idea that there is a lower limit to divisibility is sometimes taken as an answer to Zeno’s paradoxes about the impossibility of traversing infinitely divisible magnitudes (Hasper 2006). Reconstructions offered by Wardy (1988) and Sedley (2008) argue, instead, that atomism was developed as a response to Parmenidean arguments.

The atomists held that there are two fundamentally different kinds of realities composing the natural world, atoms and void. Atoms, from the Greek adjective atomos or atomon , ‘indivisible,’ are infinite in number and various in size and shape, and perfectly solid, with no internal gaps. They move about in an infinite void, repelling one another when they collide or combining into clusters by means of tiny hooks and barbs on their surfaces, which become entangled. Other than changing place, they are unchangeable, ungenerated and indestructible. All changes in the visible objects of the world of appearance are brought about by relocations of these atoms: in Aristotelian terms, the atomists reduce all change to change of place. Macroscopic objects in the world that we experience are really clusters of these atoms; changes in the objects we see—qualitative changes or growth, say—are caused by rearrangements or additions to the atoms composing them. While the atoms are eternal, the objects compounded out of them are not. Clusters of atoms moving in the infinite void come to form kosmoi or worlds as a result of a circular motion that gathers atoms up into a whirl, creating clusters within it (DK 68B167); these kosmoi are impermanent. Our world and the species within it have arisen from the collision of atoms moving about in such a whirl, and will likewise disintegrate in time.

In supposing that void exists, the atomists deliberately embraced an apparent contradiction, claiming that ‘what is not’ exists. Apparently addressing an argument by Melissus, a follower of Parmenides, the atomists paired the term for ‘nothing’ with what it negates, ‘thing,’ and claimed that—in a phrase typical of the atomists—the one ‘no more’ exists than the other (DK 67A6). Schofield (2002) argues that this particular phrase originated with Democritus and not his teacher Leucippus. By putting the full (or solid) and the void ontologically on a par, the atomists were apparently denying the impossibility of void. Void they considered to be a necessary condition for local motion: if there were no unoccupied places, where could bodies move into? Melissus had argued from the impossibility of void to the impossibility of motion; the atomists apparently reasoned in reverse, arguing from the fact that motion exists to the necessity for void space to exist (DK 67A7). It has been suggested that Democritus’ conception of void is that of the (temporarily) unfilled regions between atoms rather than a concept of absolute space (Sedley 1982). Void does not impede the motion of atoms because its essential quality is that of ‘yielding,’ in contrast to the mutual resistance of atoms. Later atomist accounts attest that this ‘yielding’ explains the tendency of bodies to drift into emptier spaces, driven out by collision from more densely packed regions (Lucretius DRN 6.906–1089).

Some controversy surrounds the properties of the atoms. They vary in size: one report—which some scholars question—suggests that atoms could, in principle, be as large as a cosmos, although at least in this cosmos they all seem to be too small to perceive (DK 68A47). They can take on an infinite variety of shapes: there are reports of an argument that there is ‘no more’ reason for the atoms to be one shape than another. Many kinds of atoms can interlock with one another because of their irregular shapes and hooks at their surface, accounting for the cohesiveness of some compounds. It is not clear whether the early atomists regarded atoms as conceptually indivisible or merely physically indivisible (Furley 1967). The idea that there is a smallest possible magnitude seems to suggest that this is the lower limit of size for atoms, although notions like being in contact or having shape seem to entail that even the smallest atoms have parts in some sense, if only mathematically or conceptually.

There are conflicting reports on whether atoms move in a particular direction as a result of their weight: a number of scholars have tried to reconcile these by supposing that weight is not intrinsic to the atoms, but is a result of the centripetal tendencies set up in the cosmic whirl (cf. O’Brien 1981; Furley 1989, pp. 91–102). Atoms may have an inherent tendency to a kind of vibratory motion, although the evidence for this is uncertain (McDiarmid 1958). However, their primary movement seems to result from collision with other atoms, wherein their mutual resistance or antitupia causes them to move away from one another when struck. Democritus is criticized by Aristotle for supposing that the sequence of colliding atoms has no beginning, and thus for not offering an explanation of the existence of atomic motion per se , even though the prior collision with another atom can account for the direction of each individual atomic motion (see O’Keefe 1996). Although the ancient atomists are often compared to modern ‘mechanistic’ theories, Balme warned of the danger of assuming that the atomists share modern ideas about the nature of atomic motion, particularly the idea that motion is inertial (Balme 1941).

According to different reports, Democritus ascribed the causes of things to necessity, and also to chance. Probably the latter term should be understood as ‘absence of purpose’ rather than a denial of necessity (Barnes 1982, pp. 423–6). Democritus apparently recognized a need to account for the fact that the disorderly motion of individual distinct atoms could produce an orderly cosmos in which atoms are not just randomly scattered, but cluster to form masses of distinct types. He is reported to have relied on a tendency of ‘like to like’ which exists in nature: just as animals of a kind cluster together, so atoms of similar kinds cluster by size and shape. He compares this to the winnowing of grains in a sieve, or the sorting of pebbles riffled by the tide: it is as if there were a kind of attraction of like to like (DK 68B164). Although this claim has been interpreted differently (e.g. Taylor 1999b p. 188), it seems to be an attempt to show how an apparently ordered arrangement can arise automatically, as a byproduct of the random collisions of bodies in motion (Furley 1989, p. 79). No attractive forces or purposes need be introduced to explain the sorting by the tide or in the sieve: it is probable that this is an attempt to show how apparently orderly effects can be produced without goal-directioned forces or purpose.

Democritus regards the properties of atoms in combination as sufficient to account for the multitude of differences among the objects in the world that appears to us. Aristotle cites an analogy to the letters of the alphabet, which can produce a multitude of different words from a few elements in combinations; the differences all stem from the shape ( schêma ) of the letters, as A differs from N; by their arrangement ( taxis ), as AN differs from NA; and by their positional orientation ( thesis ), as N differs from Z (DK 67A6). These terms are Aristotle’s interpretation of Democritus’ own terminology, which has a more dynamic sense (Mourelatos 2004). This passage omits differences of size, perhaps because it is focused on the analogy to letters of the alphabet: it is quite clear from other texts that Democritus thinks that atoms also differ in size.

He famously denies that perceptible qualities other than shape and size (and, perhaps, weight) really exist in the atoms themselves: one direct quotation surviving from Democritus claims that ‘by convention sweet and by convention bitter, by convention hot, by convention cold, by convention color; but in reality atoms and void’ (DK 68B9, trans. Taylor 1999a). There are different accounts of this distinction. Furley argues that the translation ‘convention’ should not be taken to suggest that there is anything arbitrary about the perception of certain colors, say: the same configuration of atoms may be regularly associated with a given color (Furley 1993; cf. Barnes 1982, pp. 370–7). What Democritus rejects with the label ‘merely conventional’ is, perhaps, the imputation of the qualities in question to the atoms, or perhaps even to macroscopic bodies. Mourelatos (2005) draws the contrast as that between intrinsic and relational properties.

While several reports of Democritus’ view, apparently direct quotations, mention exclusively sensible qualities as being unreal, a report of Plutarch includes in the list of things that exist only by convention the notion of ‘combination’ or sunkrisis . If this report is genuinely Democritean, it would broaden the scope of the claim considerably: the idea that any combination—by which he presumably means any cluster of atoms—is ‘unreal’ or merely ‘conventional’ suggests that Democritus is drawing a more radical distinction than that between sensible and nonsensible qualities. The implication would be that anything perceived, because it is a perception of combinations of atoms and not atoms themselves, would be suspect, not merely the qualia experienced by means of individual sense organs. One report indeed attributes to Democritus a denial that two things could become one, or vice versa (DK 68A42), thus suggesting that combinations are regarded as conventional.

Commentators differ as to the authenticity of Plutarch’s report. As the word sunkrisis does not occur in other reports, Furley (following Sandbach) suggests that it is most likely an error for pikron , ‘bitter’ which occurs instead in another report. However, Furley concedes that Plutarch at least understands the earliest atomists to be committed to the view that all combinations of atoms, as much as sensible qualities, should be understood as conventional rather than real (Furley 1993 pp. 76–7n7). This would suggest that everything at the macroscopic level—or, strictly, everything available to perception—is regarded as unreal. The ontological status of arrangement or combination of atoms for Democritus is a vexed question, that affects our understanding of his metaphysics, his historical relationship to Melissus, and the similarity of his views to the modern primary-secondary quality distinction (Wardy 1988; Curd 1998; Lee 2005; Mourelatos 2005; Pasnau 2007). If we take the ‘conventionality’ thesis to be restricted to sensible qualities, there is still an open question about Democritus’ reason for denying their ‘reality’ (Wardy 1988; O’Keefe 1997; Ganson 1999).

Democritus’ theory of perception depends on the claim that eidôla or images, thin layers of atoms, are constantly sloughed off from the surfaces of macroscopic bodies and carried through the air. Later atomists cite as evidence for this the gradual erosion of bodies over time. These films of atoms shrink and expand; only those that shrink sufficiently can enter the eye. It is the impact of these on our sense organs that enables us to perceive. Visible properties of macroscopic objects, like their size and shape, are conveyed to us by these films, which tend to be distorted as they pass through greater distances in the air, since they are subject to more collisions with air atoms. A different or complementary account claims that the object seen impresses the air by the eidôla , and the compacted air thus conveys the image to the eye (DK 68A135; Baldes 1975). The properties perceived by other senses are also conveyed by contact of some kind. Democritus’ theory of taste, for example, shows how different taste sensations are regularly produced by contact with different shapes of atoms.

Theophrastus, who gives us the most thorough report of Democritus’ theory, criticizes it for raising the expectation that the same kinds of atoms would always cause similar appearances. However, it may be that most explanations are directed towards the normal case of a typical observer, and that a different account is given as to the perceptions of a nontypical observer, such as someone who is ill. Democritus’ account why honey sometimes tastes bitter to people who are ill depends on two factors, neither of which undercut the notion that certain atomic shapes regularly affect us in a given way. One is that a given substance like honey is not quite homogeneous, but contains atoms of different shapes. While it takes its normal character from the predominant type of atom present, there are other atom-types present within. The other is that our sense-organs need to be suitably harmonized to admit a given atom-type, and the disposition of our passageways can be affected by illness or other conditions. Thus someone who is ill may become unusually receptive to an atom-type that is only a small part of honey’s overall constitution.

Other observed effects, however, require a theory whereby the same atoms can produce different effects without supposing that the observer has changed. The change must then occur in the object seen. The explanation of color seems to be of this variety: Aristotle reports that things acquire their color by ‘turning,’ tropê ( GC 1.2, 315b34). This is the Democritean term that Aristotle had translated as ‘position,’ thesis , i.e. one of the three fundamental ways in which atoms can alter and thus appear differently to us. Aristotle gives this as the reason why color is not ascribed to the atoms themselves. Lucretius’ account of why color cannot belong to atoms may help clarify the point here. We are told that if the sea’s atoms were really blue, they could not undergo some change and look white ( DRN 2.774–5), as when we observe the sea’s surface changing from blue to white. This seems to assume that, while an appearance of a property P can be produced by something that is neither P nor not-P, nonetheless something P cannot appear not-P. Since atoms do not change their intrinsic properties, it seems that change in a relational property, such as the relative position of atoms, is most likely to be the cause of differing perceptions. In the shifting surface of the sea or the flutter of the pigeon with its irridescent neck, it is evident that the parts of the object are moving and shifting in their positional relations.

By ascribing the causes of sensible qualities to relational properties of atoms, Democritus forfeits the prima facie plausibility of claiming that things seem P because they are P. Much of Theophrastus’ report seems to focus on the need to make it plausible that a composite can produce an appearance of properties it does not intrinsically possess. Democritus is flying in the face of at least one strand of commonsense when he claims that textures produce the appearance of hot or cold, impacts cause colour sensations. The lists of examples offered, drawing on commonsense associations or anecdotal experience, are attempts to make such claims persuasive. Heat is said to be caused by spherical atoms, because these move freely: the commonsense association of quick movement with heating may be employed here. Betegh (2020) suggests that larger void spaces are directly associated with heating, rather than that rarefaction indirectly causes heat by allowing freer and more frequent atomic motion.

Aristotle sometimes criticizes Democritus for claiming that visible, audible, olfactory and gustatory sensations are all caused by touch (DK 68A119). Quite how this affects the account of perception is not clear, as the sources tells us little about how touch is thought to work. Democritus does not, however, seem to distinguish between touch and contact, and may take it to be unproblematic that bodies communicate their size, shape and surface texture by physical impact.

In common with other early ancient theories of living things, Democritus seems to have used the term psychê to refer to that distinctive feature of living things that accounts for their ability to perform their life-functions. According to Aristotle, Democritus regarded the soul as composed of one kind of atom, in particular fire atoms. This seems to have been because of the association of life with heat, and because spherical fire atoms are readily mobile, and the soul is regarded as causing motion. Democritus seems to have considered thought to be caused by physical movements of atoms also. This is sometimes taken as evidence that Democritus denied the survival of a personal soul after death, although the reports are not univocal on this.

One difficulty faced by materialist theories of living things is to account for the existence and regular reproduction of functionally adapted forms in the natural world. Although the atomists have considerable success in making it plausible that a simple ontology of atoms and void, with the minimal properties of the former, can account for a wide variety of differences in the objects in the perceptible world, and also that a number of apparently orderly effects can be produced as a byproduct of disorderly atomic collisions, the kind of functional organization found in organisms is much harder to explain.

Democritus seems to have developed a view of reproduction according to which all parts of the body contribute to the seed from which the new animal grows, and that both parents contribute seed (DK 68A141; 143). The theory seems to presuppose that the presence of some material from each organ in the seed accounts for the development of that organ in the new organism. Parental characteristics are inherited when the contribution of one or other parent predominates in supplying the appropriate part. The offspring is male or female according to which of the two seeds predominates in contributing material from the genitals. In an atomist cosmos, the existence of particular species is not considered to be eternal. Like some other early materialist accounts, Democritus held that human beings arose from the earth (DK 68A139), although the reports give little detail.

One report credits Democritus and Leucippus with the view that thought as well as sensation are caused by images impinging on the body from outside, and that thought as much as perception depends on images (DK 67A30). Thought as well as perception are described as changes in the body. Democritus apparently recognized that his view gives rise to an epistemological problem: it takes our knowledge of the world to be derived from our sense experience, but the senses themselves not to be in direct contact with the nature of things, thus leaving room for omission or error. A famous fragment may be responding to such a skeptical line of thought by accusing the mind of overthrowing the senses, though those are its only access to the truth (DK68B125). Other passages talk of a gap between what we can perceive and what really exists (DK 68B6–10; 117). But the fact that atoms are not perceptible means that our knowledge of their properties is always based on analogy from the things of the visible world. Moreover, the senses report properties that the atoms don’t really possess, like colors and tastes. Thus the potential for doubt about our knowledge of the external world looms large.

Later philosophers adapted a Democritean phrase ou mallon or ‘no more’ in the argument that something that seems both P and not-P is ‘no more’ P than not-P. Arguments of this form were used for sceptical purposes, citing the conflicting evidence of the senses in order to raise concern about our knowledge of the world (de Lacy 1958). Democritus does not seem to be pursuing a consistently skeptical program, although he does express concern about the basis for our knowledge.

The idea that our knowledge is based on the reception of images from outside us is employed in Democritus’ discussion of the gods, wherein it is clear that our knowledge of the gods comes from eidôla or giant films of atoms with the characteristics we attribute to the gods, although Democritus denies that they are immortal. Some scholars take this to be a deflationary attack on traditional theology as based on mere images (Barnes 1982, pp. 456–61), but others suppose that the theory posits that these eidôla are really living beings (Taylor 1999a, pp. 211–6). Although atomism is often identified as an atheist doctrine in later times, it is not clear whether this is really Democritus’ view.

The reasons for supposing that there are indivisible magnitudes apparently stem from Zeno of Elea’s account of paradoxes that arise if extension is understood to be infinitely divisible, i.e. composed of an infinite number of parts. The atomists may have sought to avoid these paradoxes by supposing that there is a limit to divisibility.

It is not clear, however, in what sense the atoms are said to be indivisible, and how the need for smallest magnitudes is related to the claim that atoms are indivisible. Furley suggests that the atomists may not have distinguished between physical and theoretical indivisibility of the atoms (Furley 1967, p. 94). The physical indivisibility of the atoms seems to be independent of the argument for indivisible magnitudes, since the solidity of atoms—the fact that there is no void within them—is said to be the reason why they cannot be split. The existence of void space between atoms is cited as the reason why they can be separated: one late source, Philoponus, even suggests that atoms could never actually touch, lest they fuse (DK 67A7). Whether or not Democritus himself saw this consequence, it seems that atoms are taken to be indivisible whatever their size. Presumably, though, there is a smallest size of atom, and this is thought to be enough to avoid the paradoxes of infinite divisibility.

A reductio ad absurdum argument reported by Aristotle suggests that the atomists argued from the assumption that, if a magnitude is infinitely divisible, nothing prevents it actually having been divided at every point. The atomist then asks what would remain: if the answer is some extended particles, such as dust, then the hypothesized division has not yet been completed. If the answer is nothing or points, then the question is how an extended magnitude could be composed from what does not have extension (DK 68A48b, 123).

Democritus is also said to have contributed to mathematics, and to have posed a problem about the nature of the cone. He argues that if a cone is sliced anywhere parallel to its base, the two faces thus produced must either be the same in size or different. If they are the same, however, the cone would seem to be a cylinder; but if they are different, the cone would turn out to have step-like rather than continuous sides. Although it is not clear from Plutarch’s report how (or if) Democritus solved the problem, it does seem that he was conscious of questions about the relationship between atomism as a physical theory and the nature of mathematical objects.

The reports concerning Democritus’ ethical views pose a number of interpretative problems, including the difficulty of deciding which fragments are genuinely Democritean (see above, section 1). In contrast to the evidence for his physical theories, many of the ethical fragments are lists of sayings quoted without context, rather than critical philosophical discussions of atomist views. Many seem like commonsense platitudes that would be consistent with quite different philosophical positions. Thus, despite the large number of ethical sayings, it is difficult to construct a coherent account of his ethical views. Annas notes the Socratic character of a number of the sayings, and thinks there is a consistent theme about the role of one’s own intellect in happiness (Annas 2002). The sayings contain elements that can be seen as anticipating the more developed ethical views of Epicurus (Warren 2002).

It is also a matter of controversy whether any conceptual link can be found between atomist physics and the ethical commitments attributed to Democritus. Vlastos argued that a number of features of Democritus’ naturalistic ethics can be traced to his materialist account of the soul and his rejection of a supernatural grounding for ethics (Vlastos 1975). Taylor is more sceptical about the closeness of the connection between Democritus’ ethical views and his atomist physics (Taylor 1999a, pp. 232–4).

The reports indicate that Democritus was committed to a kind of enlightened hedonism, in which the good was held to be an internal state of mind rather than something external to it (see Hasper 2014). The good is given many names, amongst them euthymia or cheerfulness, as well as privative terms, e.g. for the absence of fear. Some fragments suggest that moderation and mindfulness in one’s pursuit of pleasures is beneficial; others focus on the need to free oneself from dependence on fortune by moderating desire. Several passages focus on the human ability to act on nature by means of teaching and art, and on a notion of balance and moderation that suggests that ethics is conceived as an art of caring for the soul analogous to medicine’s care for the body (Vlastos 1975, pp. 386–94). Others discuss political community, suggesting that there is a natural tendency to form communities.

Although the evidence is not certain, Democritus may be the originator of an ancient theory about the historical development of human communities. In contrast to the Hesiodic view that the human past included a golden age from which the present day is a decline, an alternative tradition that may derive from Democritus suggests that human life was originally like that of animals; it describes the gradual development of human communities for purposes of mutual aid, the origin of language, crafts and agriculture. Although the text in question does not mention Democritus by name, he is the most plausible source (Cole 1967; Cartledge 1997).

If Democritus is the source for this theory, it suggests that he took seriously the need to account for the origin of all aspects of the world of our experience. Human institutions could not be assumed to be permanent features or divine gifts. The explanations offered suggest that human culture developed as a response to necessity and the hardships of our environment. It has been suggested that the sheer infinite size of the atomist universe and thus the number of possible combinations and arrangements that would occur by chance alone are important in the development of an account that can show how human institutions arise without assuming teleological or theological origins (Cole 1967). Although here, as on other questions, the evidence is less than certain, it is plausible that Democritus developed a powerful and consistent explanation of much of the natural world from a very few fundamentals.

For the reception and subsequent history of Democritean atomism, see the related entry on ancient atomism.

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• –––, 1997, ‘The Ontological Status of Sensible Qualities for Democritus and Epicurus,’ Ancient Philosophy , 17: 119–34.
• Osborne, Catherine, 2004, Presocratic Philosophy: A Very Short Introduction , Oxford: Oxford University Press.
• Pasnau, Robert, 2007, ‘Democritus and Secondary Qualities,’ Archiv für Geschichte der Philosophie , 89: 99–121.
• Schofield, Malcolm, 2002, ‘Leucippus, Democritus and the ou mallon Principle: An Examination of Theophrastus Phys. Op. Fr. 8,’ Phronesis , 47(3): 253–63.
• Sedley, David, 1982, ‘Two Conceptions of Vacuum,’ Phronesis , 27: 175–93.
• Sedley, David, 2008, ‘Atomism’s Eleatic Roots,’ in Patricia Curd and Daniel W. Graham (eds.), The Oxford Handbook of Presocratic Philosophy , Oxford: Oxford University Press, 305–332.
• Sorabji, Richard, 1983, Time, Creation and the Continuum , London: Duckworth.
• Taylor, C.C.W., 2007, ‘Nomos and Phusis in Democritus and Plato,’ Social Philosophy and Policy , 24 (2): 1–20.
• Vlastos, G., 1975, ‘Ethics and physics in Democritus,’ in D.J. Furley and R.E. Allen (eds.), Studies in Presocratic Philosophy (Volume 2: Eleatics and Pluralists ), London: Routledge and Kegan Paul, pp. 381–408.
• Wardy, Robert, 1988, ‘Eleatic Pluralism,’ Archiv für Geschichte der Philosophie , 70: 125–46.
• Warren, James, 2002, Epicurus and Democritean Ethics: An Archaeology of Ataraxia , Cambridge: Cambridge University Press.
• Zilioli, Ugo (ed.), 2021, Atomism in Philosophy: A History from Antiquity to the Present , London: Bloomsbury.

How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.

• Translation of S. Luria’s Demokrit , by C.C.W. Taylor (must be registered at academia.edu).

atomism: ancient | doxography of ancient philosophy | Epicurus | Leucippus | Lucretius | -->Melissus --> | Parmenides | Zeno of Elea | Zeno of Elea: Zeno’s paradoxes

Acknowledgments

I wish to thank the ancient philosophy editor John Cooper, A.P.D. Mourelatos and Tim O’Keefe for helpful comments and suggestions.

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How did Democritus contribute to the atomic model? Democritus atom model

How did the democritus model evolve, what is the atomist doctrine, the legacy of democritus, democritus’s biography.

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Ancient physics: How Democritus predicted the atom

Credit: vinap via Adobe Stock / Public Domain via Wikimedia

• The idea of the atom goes as far back as the ancient Greek philosopher Democritus in about 400 B.C.E.
• This led to his “theory of eidôla” to explain how our minds create the illusion of reality.
• Democritus was one of the first determinists, arguing that a world made only of atoms and controlled by the laws of physics left no room for free will.

Philosophers love “The Matrix”.

It’s the perfect introduction to the ideas of big names such as Plato and Descartes but with leather trench coats, bullet time, and a brooding Keanu Reeves. One of the most memorable moments in the movie comes near the end when the protagonist, Neo, finally understands the Matrix for the illusionary simulation that it is. Now, he can see the numbers underpinning everything. He can see the source code of the world.

With only the slightest of modifications, Neo’s epiphany is no science fiction at all. This is how the world is made. But, where Neo saw green, floating numbers, we now know the universe is actually made up of tiny, imperceptible objects. Rather than code, we have atoms—the building blocks of everything there is, ever was, and ever will be.

We know atoms exist thanks to scientists and electron microscopes, but the idea goes much further back than that. It goes back to the ancient Greeks. Their output was prodigious. Almost every discipline you can study, the Greeks turned their minds to first. Pythagoras laid the foundation for math and geometry, Aristotle contemplated biology and physics, Plato thought about governance, Herodotus was a historian, and Hippocrates gave doctors his eponymous oath. But one of the most ingenious “firsts” must come with the atomists, like Democritus or Epicurus.

It’s odd to think that millennia ago, a few bearded men in togas, strolling around a sun-bleached agora, used philosophy to establish the fundamental fabric of the universe.

Although the idea of “the atom” had been floating around the Peloponnese for a while, Democritus was the first to articulate it fully. He argued that atoms must exist because the alternative is sheer nonsense. If we could constantly divide or cut a thing into two then we would go on forever. We’d get smaller and smaller all the way to infinity, and there’d be no end point. But the universe can’t be built without foundations. Nothing can come from nothing. So, there must be a fundamental unit to the world from which everything else is made, and for this, Democritus coined the term “atom” (which literally means uncuttable, although 20th Century scientists learned how to split one, rather ruining the definition).

The question now facing Democritus was how these basic, imperceptible atoms came to make the objects we all see, touch, and love. He noted how, when we look at the world around us, we can see it constantly changing, shifting, dying, and growing. The world flows. So atoms, which make up everything there is, must themselves be moving. They can’t just be inert or still.

Democritus argued that atoms come together in various combinations, and then emit something called an “ eidôla. ” These composite blobs of atoms radiate eidôla outward, like ripples in water. The eidôla are then picked up by us as the subjective experiencer and we translate this atomic radiation into ideas or sensations.

For example, let’s imagine a group of atoms come together and, with a special wiggle, emit their eidôla . This flies through the space (or “void,” as Democritus called it) to our eyes. Our eyes then whizz this eidôla along to our understanding, where it’s converted into “blue” or “round” or “big.”

There were two big implications to Democritus’ theory.

First, the world as we know it doesn’t actually exist. Just like the code in the Matrix, the world is really just incomprehensible atoms. Our minds create “reality” out of these atoms, and everything is just an illusion we play on ourselves.

Second, the world is entirely made up of atoms. The tree outside, your pet turtle, your feeling of love, and even the mind that processes eidôla are all made up of atoms.

The upshot of this is that Democritus was one of the first “determinists” in that he thought there could be no free will or choice. We’re all just marbles, bouncing around to the laws of physics.

We might think this a pretty depressing place to finish, yet Democritus was actually known as “the laughing philosopher.” He simply refused to take anything seriously. If reality was ultimately the invented story of our minds, and the universe was just physical laws, what’s the point in getting wound up by things? Why stress about that email from your boss, or that mean thing a friend said when there’s nothing we can do anyway? If the world is an illusion, and a boringly scripted one at that, why not laugh?

The first “atomist,” Democritus, of course got a lot wrong, but it’s remarkable how much he got right. By reflecting on reality long enough, he came to conclusions that scientists proved millennia later. If nothing else, he offers a shining example of the power of contemplation.

Jonny Thomson teaches philosophy in Oxford. He runs a popular Instagram account called Mini Philosophy (@ philosophyminis ). His first book is Mini Philosophy: A Small Book of Big Ideas .

Universe Today

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Who Was Democritus?

As the philosopher Nietzsche famously said “He who would learn to fly one day must first learn to stand and walk and run and climb and dance; one cannot fly into flying.” This is certainly true when it comes to humanity’s understanding of the universe, something which has evolved over many thousands of years and been the subject of ongoing discovery.

And along the way, many names stand out as examples of people who achieved breakthroughs and helped lay the foundations of our modern understanding. One such person is Democritus, an ancient Greek philosopher who is viewed by many as being the “father of modern science”. This is due to his theory of universe that is made up of tiny “atoms”, which bears a striking resemblance to modern atomic theory.

Though he is typically viewed as one of Greece’s many pre-Socratic natural philosopher, many historians have argued that he is more rightly classified as a scientist, at least when compared to his contemporaries. There has also been significant controversy – particularly in Germany during the 19th century – over whether or not Democritus deserves credit for atomic theory.

This argument is based on the relationship Democritus had with contemporary philosopher Leucippus, who is renowned for sharing his theory about atoms with him. However, their theories came down to a different basis, a distinction that allows Democritus to be given credit for a theory that would go on to become a staple of the modern scientific tradition.

Birth and Early Life:

The precise date and location of Democritus birth is the subject the debate. While most sources claim he was born in Abdera, located in the northern Greek province of Thrace, around 460 BCE. However, other sources claim he was born in Miletus, a coastal city of ancient Anatolia and modern-day Turkey, and that he was born in 490 BCE.

It has been said that Democritus’ father was from a noble family and so wealthy that he received the Persian king Xerxes on the latter’s march through Abdera during the Second Persian War (480–479 BC). It is further argued that as a reward for his service, the Persian monarch gave his father and other Abderites gifts, and left several Magi among them. Democritus was apparently instructed by these Magi in astronomy and theology.

After his father had died, Democritus used his inheritance to finance a series of travels to distant countries. Desiring to feed his thirst for knowledge, Democritus traveled extensively across the known world, traveling to Asia, Egypt and (according to some sources) venturing as far as India and Ethiopia. His writings include descriptions of the the cities of Babylon and Meroe (in modern-day Sudan).

Upon returning to his native land, he occupied himself with the study of natural philosophy. He also traveled throughout Greece to acquire a better knowledge of its cultures and learned from many of Greece’s famous philosophers. His wealth allowed him to purchase their writings, and he wrote of them in his own works. In time, he would become one of the most famous of the pre-Socratic philosophers.

Leucippus of Miletus had the greatest influence on him, becoming his mentor and sharing his theory of atomism with him. Democritus is also said to have known Anaxagoras, Hippocrates and even Socrates himself (though this remains unproven). During his time in Egypt, he learned from Egyptian mathematicians, and is said to have become acquainted with the Chaldean magi in Assyria.

In the tradition of the atomists, Democritus was a thoroughgoing materialists who viewed the world in terms of natural laws and causes. This differentiated him from other Greek philosophers like Plato and Aristotle, for whom philosophy was more teleological in nature – i.e. more concerned with the purpose of events rather than the causes, as well things like essence, the soul, and final causes.

According to the many descriptions and anecdotes about Democritus, he was known for his modesty, simplicity, and commitment to his studies. One story claims he blinded himself on purpose in order to be less distracted by worldly affairs (which is believed to be apocryphal). He was also known for his sense of humor and is commonly referred to as the “Laughing Philosopher” – for his capacity to laugh at human folly. To his fellow citizens, he was also known as “The Mocker”.

Scientific Contributions:

Democritus is renowned for being a pioneer of mathematics and geometry. He was among the first Greek philosophers to observe that a c one or pyramid has one-third the volume of a cylinder or prism with the same base and height. While none of his works on the subject survived the Middle Ages, his mathematical proofs are derived from other works with contain extensive citations to titles like On Numbers, On Geometrics, On Tangencies , On Mapping , and On Irrationals.

Democritus is also known for having spent much of his life experimenting with and examining plants and minerals. Similar to his work in mathematics and geometry, citations from existing works are used to infer the existence of works on the subject. These include On the Nature of Man , the two-volume collection On Flesh , On Mind, On the Senses , On Flavors , On Colors , Causes concerned with Seeds and Plants and Fruits , and to the three-volume collection Causes concerned with Animals.

From his examination of nature, Democritus developed what could be considered some of the first anthropological theories. According to him, human beings lived short lives in archaic times, forced to forage like animals until fear of wild animals then drove them into communities. He theorized that such humans had no language, and only developed it through the need to articulate thoughts and ideas.

Through a process of trial and error, human beings developed not only verbal language, but also symbols with which to communicate (i.e. written language), clothing, fire, the domestication of animals, and agriculture. Each step in this process led to more discoveries, more complex behaviors, and the many things that came to characterize civilized society.

In terms of astronomy and cosmology, Democritus was a proponent of the spherical Earth hypothesis. He believed that in the original chaos from which the universe sprang, the universe was composed of nothing but tiny atoms that came together to form larger units (a theory which bears a striking resemblance to The Big Bang Theory and Nebular Theory ). He also believed in the existence of many worlds, which were either in state of growth or decay.

In a similar vein, Democritus advanced a theory of void which challenged the paradoxes raised by his fellow Greek philosophers, Parmenides and Zeno – the founders of metaphysical logic. According to these men, movement cannot exist because such a thing requires there to be a void – which is nothing, and therefore cannot exist. And a void cannot be termed as such if it is in fact a definable, existing thing.

To this, Democritus and other atomists argued that since movement is an observable phenomena, there must be a void. This idea previewed Newton’s theory of absolute space, in which space exists independently of any observer or anything external to it. Einstein’s theory of relativity also provided a resolution to the paradoxes raised by Parmenides and Zeno, where he asserted that space itself is relative and cannot be separated from time.

Democritus’ thoughts on the nature of truth also previewed the development of the modern scientific method. According to Democritus, truth is difficult, because it can only be perceived through senses-impressions which are subjective. Because of this, Aristotle claimed in his Metaphysics that Democritus was of the opinion that “either there is no truth or to us at least it is not evident.”

However, as Diogenes Laertius quoted in his 3rd century CE tract, Lives and Opinions of Eminent Philosophers : “By convention hot, by convention cold, but in reality atoms and void, and also in reality we know nothing, since the truth is at bottom.”

Ultimately, Democritus’ opinion on truth came down to a distinction between two kinds of knowledge – “legitimate” (or “genuine”) and bastard (or “secret”). The latter is concerned with perception through the senses, which is subjective by nature. This is due to the fact that our sense-perception are influence by the shape and nature of atoms as they flow out from the object in question and make an impression on our senses.

“Legitimate” knowledge, by contrast, is achieved through the intellect, where sense-data is elaborated through reasoning. In this way, one can get from “bastard” impressions to the point where things like connections, patterns and causality can be determined. This is consistent with the inductive reasoning method later elaborated by Renee Descartes, and is a prime example of why Democritus is considered to be an early scientific thinker.

Atomic Theory:

However, Democritus greatest contribution to modern science was arguably the atomic theory he elucidated. According to Democritus’ atomic theory, the universe and all matter obey the following principles:

• Everything is composed of “atoms”, which are physically, but not geometrically, indivisible
• Between atoms, there lies empty space
• Atoms are indestructible
• Atoms have always been, and always will be, in motion
• There are an infinite number of atoms, and kinds of atoms, which differ in shape, and size.

He was not alone in proposing atomic theory, as both his mentor Leucippus and Epicurus are believed to have proposed the earliest views on the shapes and connectivity of atoms. Like Democritus, they believed that the solidity of a material corresponded to the shape of the atoms involved – i.e. iron atoms are hard, water atoms are smooth and slippery, fire atoms are light and sharp, and air atoms are light and whirling.

However, Democritus is credited with illustrating and popularizing the concept, and for his descriptions of atoms which survived classical antiquity to influence later philosophers. Using analogies from our sense experiences, Democritus gave a picture or an image of an atom that distinguished them from each other by their shape, size, and the arrangement of their parts.

In essence, this model was one of an inert solid that excluded other bodies from its volume, and which interacted with other atoms mechanically. As such, his model included physical links (i.e. hooks and eyes, balls and sockets) that explained how connections occurred between them. While this bears little resemblance to modern atomic theory (where atoms are not inert and interact electromagnetically), it is more closely aligned with that of modern science than any other theory of antiquity.

While there is no clear explanation as to how scholars of classical antiquity came to theorize the existence of atoms, the concept proved to be influential, being picked up by Roman philosopher Lucretius in the 1st century CE and again during the Scientific Revolution. In addition to being indispensable to modern molecular and atomic theory, it also provided an explanation as to why the concept of a void was necessary in nature.

If all matter was composed of tiny, indivisible atoms, then there must also be a great deal of open space between them. This reasoning has also gone on to inform out notions of cosmology and astronomy, where Einstein’s theory of special relativity was able to do away with the concept of a “luminiferous aether” in explaining the behavior of light.

Diogenes Laertius summarized Democritus atomic theory as follows in Lives and Opinions of Eminent Philosophers:

“That atoms and the vacuum were the beginning of the universe; and that everything else existed only in opinion. That the worlds were infinite, created, and perishable. But that nothing was created out of nothing, and that nothing was destroyed so as to become nothing. That the atoms were infinite both in magnitude and number, and were borne about through the universe in endless revolutions. And that thus they produced all the combinations that exist; fire, water, air, and earth; for that all these things are only combinations of certain atoms; which combinations are incapable of being affected by external circumstances, and are unchangeable by reason of their solidity.”

Death and Legacy:

Democritus died at the age of ninety, which would place his death at around 370 BCE; though some writers disagree, with some claiming he lived to 104 or even 109. According to Marcus Aurelius’ book Meditations , Democritus was eaten by lice or vermin, although in the same passage he writes that “other lice killed Socrates”, implying that this was meant metaphorically. Since Socrates died at the hands of the Athenian government who condemned him, it is possible that Aurelius attributed Democritus death to human folly or politics.

While Democritus was highly esteemed amongst his contemporaries, there were also those who resented him. This included Plato who, according to some accounts, disliked him so much that he wished that all his books would be burned. However, Plato’s pupil Aristotle was familiar with the works of Democritus and mentioned him in both Metaphysics and Physics , where he described him as a “physicist” who did not concern himself with the ideals of form or essence.

Ultimately, Democritus is credited as being one of the founders of the modern science because his methods and theories closely resemble those of modern astronomers and physicists. And while his version of the atomic model differs greatly from our modern conceptions, his work was of undoubted value, and was a step in an ongoing process that included such scientists as John Dalton, Neils Bohr and even Albert Einstein .

As always, science is an process of continuing discovery, where new breakthroughs are built upon the foundations of the old and every generations attempts to see a little farther by standing on the shoulders of those who came before.

We have many interesting articles about atomic theory here at Universe Today. Here’s one about John Dalton’s atomic model , Neils Bohr’s atomic model , the “Plum Pudding” atomic model .

For more information, check out The History of the Atom – Democritus .

Astronomy Cast has a wonderful episode on the subject, titled Episode 392: The Standard Model – Intro

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• Introduction

Early atomic models

Dalton’s atomic model, the thomson atomic model, the rutherford atomic model, the bohr atomic model, quantum atomic model, modern atomic model.

• How is the atomic number of an atom defined?
• What was Niels Bohr’s most important discovery?
• What was the impact of Ernest Rutherford's theory?
• What did Ernest Rutherford's atomic model get right and wrong?
• What is the model of the atom proposed by Ernest Rutherford?

atomic model

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• MIT OpenCourseWare - Introduction to Solid State Chemistry - Atomic Models: Rutherford & Bohr
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atomic model , in physics , a model used to describe the structure and makeup of an atom . Atomic models have gone through many changes over time, evolving as necessary to fit experimental data . For a more in-depth discussion of the history of atomic models, see atom: development of atomic theory .

Leucippus of Miletus (5th century  bce ) is thought to have originated the atomic philosophy of the early Greeks. His famous disciple,  Democritus of Abdera , named the building blocks of matter   atomos , meaning literally “indivisible,” about 430  bce . He suggested that atoms of the four different elements (earth, air, fire, and water) are simply spheres of different sizes, thus creating one of the first atomic models. He also suggested that these atoms move around in space, and, when collisions between the spheres occur, they can rebound or stick together, causing changes to the matter of a material. His atomic model essentially consisted of solid spheres of different sizes for different types of atoms.

The Greek atomic theory is significant historically and philosophically, but it was not based on observations of nature, measurements, tests, or experiments. Instead, the Greeks used mathematics and reason almost exclusively when they wrote about physics. Because of the influence of Aristotle , who did not agree with Democritus and other proponents of atomic philosophy, this theory was basically ignored for nearly 2,000 years.

English chemist and physicist  John Dalton  converted the atomic philosophy of the Greeks into a scientific theory between 1803 and 1808. His book  A New System of Chemical Philosophy  (Part I, 1808; Part II, 1810) was the first application of atomic theory to chemistry. It provided a physical picture of how elements combine to form compounds and a phenomenological reason for believing that atoms exist. His work, together with that of  Joseph-Louis Gay-Lussac  of France and  Amedeo Avogadro  of Italy, provided the experimental foundation of atomic chemistry. Dalton used experimental results to propose a new model of the atom in which he suggested the following:

• All matter consists of extremely small particles called atoms.
• Dalton stated that atoms could not be created, destroyed, divided into smaller pieces, or transformed into atoms of other elements. He used the law of conservation of mass in the late 1700s as the basis for these conclusions .
• Dalton stated that all atoms of an element are identical in shape, size, and mass.
• Dalton suggested that two types of atoms could form molecules of different whole-number ratios. This is known to be true for such molecules as carbon monoxide and carbon dioxide —both of which are composed of carbon and oxygen atoms but which have different ratios of each.

Dalton’s atomic model was readily accepted. It incorporated the already known ideas of the law of conservation of mass, the law of definite proportions , and the law of multiple proportions and matched experimental observations.

In the years after Dalton described his atomic model, multiple experiments were performed that proved that charged particles exist. In 1897 English physicist J.J. Thomson discovered a negatively charged particle, which he called the electron . The existence of the electron showed that the 2,000-year-old conception of the atom as a homogeneous particle was wrong and that in fact the atom has a complex structure. Thomson noted that the Dalton model of the atom did not include the idea of charge, and he theorized that the electrons must be within the atoms of elements. He used his discovery to strongly support the so-called “plum-pudding” model of atomic structure first proposed by  Lord Kelvin . The model indicated that there were pockets of negative charges within the sphere of the atom. The advantage of the Thomson atom was that it was inherently stable: if the electrons were displaced, they would attempt to return to their original positions. 

In 1911 a former student of Thomson’s, New Zealand-born British physicist  Ernest Rutherford , in cooperation with other scientists, performed alpha particle experiments that led to the overturning of Thomson’s model . They aimed alpha particles at a thin sheet of gold foil and then recorded the location of the alpha particle with a fluorescent screen after the interaction. They found that the majority of the alpha particles passed through the gold foil as if the foil was not there. They also found that a very small number of these alpha particles deflected at angles from the initial path, with some of the alpha particles even bouncing back along the initial path.

Rutherford concluded that there must be a small, highly dense core of matter in an atom off which the alpha particles were bouncing. He theorized that this atomic nucleus was positively charged and surmised that the electrons orbited around it. Many physicists doubted the Rutherford atomic model because it was difficult to reconcile with the chemical behaviour of atoms. The model suggested that the charge on the nucleus was the most important characteristic of the atom, determining its structure.

In 1913, just two years after the Rutherford atomic model had been introduced, Danish physicist Niels Bohr , a student of Rutherford’s, proposed his quantized shell model of the atom ( see   Bohr model ) to explain how electrons can have stable orbits around the nucleus. The motion of the electrons in the Rutherford model was unstable because, according to classical mechanics and electromagnetic theory, any charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus. To remedy the stability problem, Bohr modified the Rutherford model by requiring that the electrons move in orbits of fixed size and energy. The energy of an electron depends on the size of the orbit and is lower for smaller orbits. Radiation can occur only when the electron jumps from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump. Bohr’s starting point was the realization that classical mechanics by itself could never explain the atom’s stability.

Bohr suggested that each orbit has a different energy level associated with it, as the distance from the nucleus determines forces acting on the electrons in the various orbits, or shells. He found that energy can be absorbed by electrons to move from a lower energy orbit to a higher energy orbit and that they release energy when moving from higher to lower energy orbits. However, despite a number of modifications to the model, by the early 1920s Bohr’s model seemed to be a dead end, as efforts to generalize the model to multielectron atoms had proved futile.

In 1926 Austrian physicist Erwin Schrödinger used mathematical equations to describe the probability of finding electrons in specific positions ( see Schrödinger equation ). These equations no longer state with certainty where electrons can be found but instead describe the region of space where it is highly probable that an electron could be found.

In 1932 English physicist James Chadwick discovered a neutral particle of approximately the same mass as the proton and located in the nucleus of the atom. This particle, now known as the neutron , completed the understanding of the three elementary particles of the atom.

Quantum mechanics continues to drive atomic theory. In the 1960s subatomic particles called quarks were found to exist. The proton is made up of two up quarks, each of which has a positive charge 2/3 that of the electron, and one down quark, which has a negative charge 1/3 that of the electron. The neutron is made up of one up quark and two down quarks and thus has no charge.

John Dalton

(1766-1844)

Who Was John Dalton?

During John Dalton's early career, he identified the hereditary nature of red-green color blindness. In 1803 he revealed the concept of Dalton’s Law of Partial Pressures. Also in the 1800s, he was the first scientist to explain the behavior of atoms in terms of the measurement of weight.

Early Life and Career

Dalton was born in Eaglesfield, England, on September 6, 1766, to a Quaker family. He had two surviving siblings. Both he and his brother were born color-blind. Dalton's father earned a modest income as a handloom weaver. As a child, Dalton longed for formal education, but his family was very poor. It was clear that he would need to help out with the family finances from a young age.

After attending a Quaker school in his village in Cumberland, when Dalton was just 12 years old he started teaching there. When he was 14, he spent a year working as a farmhand but decided to return to teaching — this time as an assistant at a Quaker boarding school in Kendal. Within four years, the shy young man was made principal of the school. He remained there until 1793, at which time he became a math and philosophy tutor at the New College in Manchester.

While at New College, Dalton joined the Manchester Literary and Philosophical Society. Membership granted Dalton access to laboratory facilities. For one of his first research projects, Dalton pursued his avid interest in meteorology. He started keeping daily logs of the weather, paying special attention to details such as wind velocity and barometric pressure—a habit Dalton would continue all of his life. His research findings on atmospheric pressure were published in his first book, Meteorological Findings , the year he arrived in Manchester.

During his early career as a scientist, Dalton also researched color blindness—a topic with which he was familiar through firsthand experience. Since the condition had affected both him and his brother since birth, Dalton theorized that it must be hereditary. He proved his theory to be true when genetic analysis of his own eye tissue revealed that he was missing the photoreceptor for perceiving the color green. As a result of his contributions to the understanding of red-green color blindness, the condition is still often referred to as "Daltonism."

Dalton's Law

Dalton's interest in atmospheric pressures eventually led him to a closer examination of gases. While studying the nature and chemical makeup of air in the early 1800s, Dalton learned that it was not a chemical solvent, as other scientists had believed. Instead, it was a mechanical system composed of small individual particles that used pressure applied by each gas independently.

Dalton's experiments on gases led to his discovery that the total pressure of a mixture of gases amounted to the sum of the partial pressures that each individual gas exerted while occupying the same space. In 1803 this scientific principle officially came to be known as Dalton's Law of Partial Pressures. Dalton's Law primarily applies to ideal gases rather than real gases, due to the elasticity and low particle volume of molecules in ideal gases. Chemist Humphry Davy was skeptical about Dalton's Law until Dalton explained that the repelling forces previously believed to create pressure only acted between atoms of the same sort and that the atoms within a mixture varied in weight and complexity.

The principle of Dalton's Law can be demonstrated using a simple experiment involving a glass bottle and large bowl of water. When the bottle is submerged under water, the water it contains is displaced, but the bottle isn't empty; it's filled with the invisible gas hydrogen instead. The amount of pressure exerted by the hydrogen can be identified using a chart that lists the pressure of water vapors at different temperatures, also thanks to Dalton's discoveries. This knowledge has many useful practical applications today. For instance, scuba divers use Dalton's principles to gauge how pressure levels at different depths of the ocean will affect the air and nitrogen in their tanks.

During the early 1800s, Dalton also postulated a law of thermal expansion that illustrated the heating and cooling reaction of gases to expansion and compression. He garnered international fame for his additional study using a crudely fashioned dew point hygrometer to determine how temperature impacts the level of atmospheric water vapor.

Atomic Theory

Dalton's fascination with gases gradually led him to formally assert that every form of matter (whether solid, liquid or gas) was also made up of small individual particles. He referred to the Greek philosopher Democritus of Abdera's more abstract theory of matter, which had centuries ago fallen out of fashion, and borrowed the term "atomos" or "atoms" to label the particles. In an article he wrote for the Manchester Literary and Philosophical Society in 1803, Dalton created the first chart of atomic weights.

Seeking to expand on his theory, he readdressed the subject of atomic weight in his book A New System of Chemical Philosophy , published in 1808. In A New System of Chemical Philosophy , Dalton introduced his belief that atoms of different elements could be universally distinguished based on their varying atomic weights. In so doing, he became the first scientist to explain the behavior of atoms in terms of the measurement of weight. He also uncovered the fact that atoms couldn't be created or destroyed.

Dalton's theory additionally examined the compositions of compounds, explaining that the tiny particles (atoms) in a compound were compound atoms. Twenty years later, chemist Amedeo Avogadro would further detail the difference between atoms and compound atoms.

In A New System of Chemical Philosophy , Dalton also wrote about his experiments proving that atoms consistently combine in simple ratios. What that meant was that the molecules of an element are always made up of the same proportions, with the exception of water molecules.

In 1810 Dalton published an appendix to A New System of Chemical Philosophy . In it he elaborated on some of the practical details of his theory: that the atoms within a given element are all exactly the same size and weight, while the atoms of different elements look—and are—different from one other. Dalton eventually composed a table listing the atomic weights of all known elements.

His atomic theories were quickly adopted by the scientific community at large with few objections. "Dalton made atoms scientifically useful," asserted Rajkumari Williamson Jones, a science historian at the University of Manchester Institute of Science and Technology. Nobel Laureate Professor Sir Harry Kroto, noted for co-discovering spherical carbon fullerenes, identified the revolutionary impact of Dalton's discoveries on the field of chemistry: "The crucial step was to write down elements in terms of their atoms...I don't know how they could do chemistry beforehand, it didn't make any sense."

From 1817 to the day he died, Dalton served as president of the Manchester Literary and Philosophical Society, the organization that first granted him access to a laboratory. A practitioner of Quaker modesty, he resisted public recognition; in 1822 he turned down elected membership to the Royal Society. In 1832 he did, however, begrudgingly accept an honorary Doctorate of Science degree from the prestigious Oxford University. Ironically, his graduation gown was red, a color he could not see. Fortunately for him, his color blindness was a convenient excuse for him to override the Quaker rule forbidding its subscribers to wear red.

In 1833 the government granted him a pension, which was doubled in 1836. Dalton was offered another degree, this time a Doctorate of Laws, by Edinburgh University in 1834. As if those honors were insufficient tribute to the revolutionary chemist, in London, a statue was erected in Dalton's honor--also in 1834. "Dalton was very much an icon for Manchester," said Rajkumari Williams Jones. "He is probably the only scientist who got a statue in his lifetime."

In his later life, Dalton continued to teach and lecture at universities throughout the United Kingdom, although it is said that the scientist was an awkward lecturer with a gruff and jarring voice. Throughout his lifetime, Dalton managed to maintain his nearly impeccable reputation as a devout Quaker. He lived a humble, uncomplicated life focusing on his fascination with science, and never married.

In 1837 Dalton had a stroke. He had trouble with his speech for the next year.

Death and Legacy

After suffering a second stroke, Dalton died quietly on the evening of July 26, 1844, at his home in Manchester, England. He was provided a civic funeral and granted full honors. A reported 40,000 people attended the procession, honoring his contributions to science, manufacturing and the nation's commerce.

By finding a way to "weigh atoms," John Dalton's research not only changed the face of chemistry but also initiated its progression into a modern science. The splitting of the atom in the 20th century could most likely not have been accomplished without Dalton laying the foundation of knowledge about the atomic makeup of simple and complex molecules. Dalton's discoveries also allowed for the cost-efficient manufacturing of chemical compounds, since they essentially give manufacturers a recipe for determining the correct chemical proportions in a given compound.

The majority of conclusions that made up Dalton's atomic theory still stand today.

"Now with nanotechnology, atoms are the centerpiece," said Nottingham University Professor of Chemistry David Garner. "Atoms are manipulated directly to make new medicines, semiconductors and plastics." He went on to further explain, "He gave us the first understanding of the nature of materials. Now we can design molecules with a pretty good idea of their properties."

In 2003, on the bicentennial of Dalton's public announcement of his atomic theory, the Manchester Museum held a tribute to the man, his life and his groundbreaking scientific discoveries.

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• Name: John Dalton
• Birth Year: 1766
• Birth date: September 6, 1766
• Birth City: Eaglesfield
• Birth Country: United Kingdom
• Gender: Male
• Best Known For: Chemist John Dalton is credited with pioneering modern atomic theory. He was also the first to study color blindness.
• Journalism and Nonfiction
• Science and Medicine
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• Astrological Sign: Virgo
• John Fletcher's Quaker grammar school
• Death Year: 1844
• Death date: July 26, 1844
• Death City: Manchester
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• Article Title: John Dalton Biography
• Author: Biography.com Editors
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• Berzelius' symbols are horrifying. A young student in chemistry might as soon learn Hebrew as make himself acquainted with them.
• We might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen.
• The principal failing in [Sir Humphrey Davy's] character as a philosopher is that he does not smoke.
• I can now enter the lecture room with as little emotion nearly as I can smoke a pipe with you on Sunday or Wednesday evenings.
• Matter, though divisible in an extreme degree, is nevertheless not infinitely divisible. That is, there must be some point beyond which we cannot go in the division of matter... I have chosen the word 'atom' to signify these ultimate particles.
• Will it not be thought remarkable that in 1836 the British chemists are ignorant whether attraction, repulsion or indifference is marked when a mixture of any proportions of azote and oxygen are made.
• In short, [London] is a most surprising place, and worth one's while to see once; but the most disagreeable place on earth for one of a contemplative turn to reside in constantly.
• To ascertain the exact quantity of water in a given quantity of air is, I presume, an object not yet fully attained.
• The cause of rain is now, I consider, no longer an object of doubt.

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Understanding Atomic Models in Chemistry: Why Do Models Change?

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Part of the book series: Science: Philosophy, History and Education ((SPHE))

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Understanding the role of early Greek philosophers (e.g., Democritus) and J. Dalton in developing the atomic theory is controversial among historians and philosophers of science. Chalmers ( The scientist’s atom and the philosopher’s stone: How science succeeded and philosophy failed to gain knowledge of atoms . Dordrecht: Springer; 2009) claims that Dalton’s theory had no testable content. On the contrary, Rocke (Email to author dated October 30, 2013, reproduced with permission; 2013) considers that Dalton’s atomism is a successful theory. A study designed to evaluate the presentation of Dalton’s atomic theory in general chemistry textbooks (published in the USA) revealed that most textbooks stated that the atomic vision of Democritus was based on hypothetical questions (thought experiments), whereas Dalton based his theory on reproducible experimental results. Another study designed to evaluate the presentation of the atomic models of J. J. Thomson, E. Rutherford, and N. Bohr in general chemistry textbooks (published in the USA) revealed that most textbooks lack a historical perspective (although historical models are being presented) and provide a simplistic view of scientific models and how these change with no reference to the difficulties and controversies involved. Exactly the same HPS-based criteria were also used to evaluate textbooks published in Turkey, Venezuela, and Korea (general physics). The similarities of the textbooks published in four countries with different cultures and languages suggest that these textbooks have an underlying common thread, namely, the dominant empiricist epistemology. Due to the difficulties faced by Bohr’s model, A. Sommerfeld postulated elliptical orbits that provided greater stability to the atoms, leading to the Bohr–Sommerfeld model. A study designed to evaluate the presentation of the Bohr–Sommerfeld model in general chemistry textbooks (published in Italy and the USA) revealed that very few presented this model satisfactorily. Once again, textbooks published in two different cultures and languages were found to be very similar. Despite its success, the Bohr–Sommerfeld model went no further than the alkali metals, which led scientists to look for other models. These difficulties were resolved by Pauli’s exclusion principle and the wave mechanical model of the atom. It is concluded that understanding of atomic structure is a never-ending quest that requires imagination, creativity, and innovative techniques in the laboratory.

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Niaz, M. (2016). Understanding Atomic Models in Chemistry: Why Do Models Change?. In: Chemistry Education and Contributions from History and Philosophy of Science. Science: Philosophy, History and Education. Springer, Cham. https://doi.org/10.1007/978-3-319-26248-2_4

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A good question, with a fascinating history. I'll answer from the perspective of electronic materials in materials science. In short, In fact, we can even manipulate individual atoms for potentially useful things (more on this later)! But this was not always the case. One of the earliest records we have on the atom came from Democritus, an ancient Greek philosopher (others like Plato and Aristotle had similar trains of thought). Democritus had a thought experiment. The idea was if you took a material and divided it half, you would have a smaller but identical chunk. If you keep dividing your material, there should eventually be a point where you've reached the smallest representative element of your material. That element is the In fact "atom" is derived from the Greek word "atomos," which roughly translates to indivisible (it turns out there are even smaller components that make up an atom, but the name stuck; see ). It wasn't until much later in the 18th and 19th centuries that significant progress towards understanding the atom was made. Our understanding of the structure of the atom has vastly changed from the model John Dalton first proposed with the development and advancement of quantum mechanics. It is the interplay between theory (e.g., quantum mechanics) and experiment that let's us characterize and engineer materials at the atomic level. Both are part of a feedback loop where e.g., experiment confirms a theoretical prediction or theory explains what is observed experimentally. Read more about the history and how our understanding of the atom changed ) (several seminal experiments that contributed to this are described). The coolest part is the fact that , and even manipulate them! is the famous image of using a scanning tunneling microscope. Each dot you see is an . Read more and . (you might have heard of nanotechnology, for instance). For example, here at UCSB, there is active research on growing materials with atomically sharp interfaces. Here is an . Each of the balls you see corresponds to a or atom; the other elements are harder to see because they are smaller/lighter, though you might be able to see the >b>Al and if you squint hard enough). This material was carefully grown using a technique called , and is being studied for its rich physics and as the next big electronic material for things like your computer and phone. Hope this helps! Best,

Nowadays we can indeed see atoms using advanced technology, like . This technology allows us to observe, or even move an individual atom. Here is a picture of the silicon atoms that scientists see using STM:

We can't see them with our eyes because they're too small, but we can build machines that can see them. In particular, , so using an x-ray camera and shining x-rays through something with an orderly arrangement of atoms (like a crystal), we can see the atoms inside of it by seeing how the x-rays scatter.

Great question. At first, scientists were not sure about what matter looked like on a very small scale. Atoms were just a theory. But scientists made a lot of other theories in chemistry that fit with the idea that matter is made up of atoms. Even though we couldn't prove these theories, many of them were useful. For example, atoms can explain why chemicals always react in the same ratios, since these chemicals are made up of atoms that must group together in the same numbers every time. We can use the STM to see details smaller than one nanometer, including atoms. has some interesting images made using the STM. We even have machines that can arrange atoms in simple patterns--many early examples of this technology show atoms arranged to spell out words or company names, like and to return to the search form. Home » Molecules » Atomic Structures » 5 Democritus Theory of Atoms – Structure – Model – Development 5 Democritus Theory of Atoms – Structure – Model – Development Post author By akbarss Post date May 15, 2017 No Comments on 5 Democritus Theory of Atoms – Structure – Model – Development Democritus is one of the most influential people in the chemistry. He was the first person who discovered the theory of atom. We know his discovery as Democritus theory of atoms. This theory is one of the most important theory in the atomic theory and organic chemistry   in general. His theory has effectively given the great foundation to understanding about atomic. Democritus theory of atoms successfully motivated other scientists to conduct other experiments and researches in atomic field. This article will cover the principles in Democritus theory of atoms, Democritus history, and other basic atomic theory. You may also read: Scientists Who Contributed to The Atomic Theory Chemistry Models of Atoms Democritus Life Biography  He was the one that inspired Democritus to make atomic theory. We mentioned this part on the previous section. He started to discover atomic theory from simple experiment in cutting stone. Democritus tried to cut stone in half and then he found out that each half of stone had the same properties as the full stone. Then he believed that if you keep cutting that stone into smaller piece, you’ll find out that that stone part is extremely small until you can not see that parts again. Then he called this very small and invisible parts as atomos. Atomos means invisible in the Greek language. He also pointed out that these atomos are unique based on its matter. He gave example that the atoms of stone have different characteristic and properties with atoms of fur. Basic Principle – Democritus Theory of Atoms The Democritus theory of atoms generally consists of 5 basic principles. Here’re some principles from Democritus atomic theory: Every matter contains the invisible parts named as atoms Atoms can not be destroyed Atoms are in solid form, but we are not able to see them Atoms are similar to each other Atoms have different properties in terms of size, form, weight, position and type of arrangement. In this theory, Democritus also described the basic properties of atoms in different type of matter as follow: In the solid matter, atoms are small and in the pointy form In the liquid matter, atoms have larger size and round form In the oil matter, atoms are in well-constructed form, smaller in size In Democritus theory of atoms we can learn that the matter consists of atoms, the invisible parts, and the empty space or void. Democritus mentioned that atoms can not be destructed nor changed. He also stated that every atom is similar to each other which means that atom has no internal structure. The atomic model of Democritus theory is in solid form. Atoms will have different kind of size, construction, location, weight and arrangement. Between the atoms, there’s void which surround them. You may also read:  Development of Atomic Theory Democritus & Leucippus Theory In making the concept of Democrtius theory of atoms, he had many inspiration from his own teacher, Leucippus. Leucippus is the author of famous book, Big Cosmology. Besides Leucippus, Democritus also mentioned that Aristotle inspired his idea about atomic structure. Even though Aristotle fought against the concept of atomic theory, but his basic concept about matter have given the good foundation for Democritus to create his atomic theory. Democritus revealed the fact that Leucippus has discovered that the atoms have infinite numbers. They are also can not be seen by our eyes. Atoms could move in the empty space or void. He stated that atoms can join to each other and then they will construct the object which can we see. This object can be destroyed if we separate the atoms away. Even though this Democritus theory of atoms is the mix between Democrtius and Leucippus, we only know Democritus as the creator for this theory. Until now, we can’t actually distinct the contribution of Democrtius and Leucippus in this theory. Rejection from Aristotle and Plato Aristotle and Plato are both one of the greatest and most influential philosopher in the world’s theory. Greek philosopher at that period tried to discover the natural world. They did the experiment and study about every phenomena in this world. They also put effort to explain the matter. At that time, both Aristotle and Plato rejected the Democritus theory of atoms. Aristotle believed that the Empedocles theory is the right one. Empedocles previously stated that all maters are constructed by 4 elements which are fire, air, water and earth. Every matter has the different ratio of these 4 elements depending on the characteristic of that matter. Aristotle then implied that these 4 elements are able to be transformed to each other. Because Aristotle was really influential at that time, almost people at that time followed the Aristotle belief in Empedocles theory. Because of Aristotle, the Democritus theory of atoms should wait for 2000 years to be rediscovered by other scientists. Weakness of Democritus theory of Atoms As the first atomic theory in the world, Democritus theory of atoms should have many flaws. Some basic weakness of this theory include: 1. Democritus was not able to describe atomic model in detail . On his theory, Democritus only stated that atoms are in the solid form in the void sphare. We can not describe the internal structure of the atom itself. We now know that Atoms consist of 3 parts which are proton, neutron and electron. 2. Democritus can not explain the chemical properties in atom Since it was the first atomic theory, we could understand that he was not able to include chemical properties to his discovery. He only mentioned that atoms have similar properties if they are in same matter. Refer to Democritus theory, atoms in stone must have same properties. While stone’s atoms will differ with fur’s atom. He only discovered the size, shape, arrangement and other physical properties of atoms. But he didn’t mentioned the chemical characteristic in atoms 3. Democritus didn’t include chemical reactions Another basic weakness of Democritus atomic theory is the fact that he didn’t mention chemical reactions in atoms. He only stated the physical model of atoms. We know later that chemical reactions between atoms are really important in chemistry study. On the following years, scientists were trying to discover chemical reactions in the atom and matter. You may read:  Proton, Electron, Neutron Dalton’s atomic theory After great invention of Democritus, In 1803 Dalton made the newer concept of atom. His theory has five basic principle as following points: All mater contains very small particles which are called atoms. He belived that atoms has the small shape and solid spheres form. He also said that atoms have various motions Atom can not be destructed and changed. The atoms in element can not be created, destroyed, divided or transformed. He used the Antoine Lavoisier theory to support this point The weight of atom determines the characteristic of atom. Dalton believed that all atoms in the same element must have same weights. Every single atoms in oxygen is same to another. While atoms in the different element will have the different characteristic from one to another. Atoms combine in the small and whole-all rations in chemical reactions. Based on Dalton’s experiment, he concluded that the chemical reactions will occur based on atom to atom ratios Atoms may combine in more than one-all ratios in element reactions. There were multiples number ratios in various compounds like oxygen compound. You may also read:  Postulates of John Dalton Atomic Theories and Scientist after Democritus Era Democritus theory of atom was the ancient theory. After Democritus era, the development of chemistry knowledge of atom had growth and more new scientist wrote new theories and experiments. Meanwhile, here are more inventions of atomic theories. 1. Thompson & Rutherford Theory Following the basic idea from Democritus and Dalton, some great scientist found out the better and detailed theory about atoms. Here’re some atomic theory after Democtritus theory of atoms. In 18977, J.J Thompson successfully discovered the electron part in the atom. He did the experiment using the cathode ray. He represented the cathode rays as the negative charge. Based on this experiment, he released the concept of atom model as the plum pudding. The raisins represented the negative charge electron while the dough represented the positive charge of atom. Ernest Rutherford, in 1911,  performed the experiment using the alpha particles. He shoot the alpha particle through the gold foil. This experiment resulted that most of the alpha particles passed through the gold foil. However, there were few alpha particles which are deflected back. Rutherford believed that there were the positive charge nucleus. in the center of atom and negative charge electron around the nucleus. You may also read:  Louis de Broglie Quantum Theories 2. Bohr Theory Neils Bohr made the new atom model in 1913. His theory consists of some principles like Electrons are located in the certain orbits around the atom’s nucleus. These orbitals are stable. Bohr called these parts as the stationary orbits Every orbit has the energy level. The differnt orbit will have the different level of energy. The orbit nereast the nucleus, as an example, will have the different energy level with the another orbit There are energy transfer in electron’s move. Electron will absorb the energy when it moves form the lower orbit to higher orbit. In contrast, electron will emit the energy when it moves from higher orbit to lower orbit The difference of orbit energy level determines the energy and frequency of light which is emitted or absorbed After these theory, we then learn other atomic theories which details these atomic models. Based on this article, we understand that Democritus’s finding in atomic theory is really useful for chemistry study. He gave the basic principle about atomic model. Even though Democritus theory of atoms has many flaws and wrong statement, we should thank Democritus for opening the door to understand atomic model. You may read: Chemical Analysis of Seawater Stereochemistry  Dangerous Chemicals Chemicals in Food Chemicals in the Brain Tags atom , atomic theory , Chemistry , Democritus Related Posts 6 differences of electrolyte and non electrolyte solutions and examples, 30 list of laboratory chemicals manufacturers in india, 18 jobs in pharmacology – description – responsibilities – salary, 7 branches of physical chemistry – fields – applications – study, 90 strong bases and weak bases examples in daily life, leave a reply cancel reply. Your email address will not be published. 384 IMAGES What Is Democritus Atomic Model Democritus's Experiment democritus atomic model Archives Honors Chemistry Atomic Theory Timeline Who Was Democritus? Democritus by barron.jannet VIDEO what is atom and who discovered atom Atomteoriens historie fra Demokrit til Rutherford Democritus PHILOSOPHY Ancient Knowledge of Atoms REVEALED 🤫 #shorts #science Thought Experiment| Discovery Of Atom| Chapter 1| Class 11| Chemistry| FBISE New Syllabus 2024 COMMENTS 4.1: Democritus' Idea of the Atom One of these philosophers was Democritus (~460-370 B.C.E.), often referred to as the "laughing philosopher" because of his emphasis on cheerfulness. He taught that there were substances called atoms and that these atoms made up all material things. The atoms were unchangeable, indestructible, and always existed. Figure 4.1.3 4.1. 3: Democritus. Democritus Democritus (born c. 460 bce —died c. 370) was an ancient Greek philosopher, a central figure in the development of philosophical atomism and of the atomic theory of the universe. Knowledge of Democritus's life is largely limited to untrustworthy tradition. It seems that he was a wealthy citizen of Abdera, in Thrace; that he traveled widely ... Democritus Atomic Model Democritus contributed to the atomic model by performing a thought experiment that first coined the notion of an "atom" from the Greek word "atomos" which means indivisible. Democritus Democritus. First published Sun Aug 15, 2004; substantive revision Sat Jan 7, 2023. Democritus, known in antiquity as the 'laughing philosopher' because of his emphasis on the value of 'cheerfulness,' was one of the two founders of ancient atomist theory. He elaborated a system originated by his teacher Leucippus into a materialist ... How did Democritus contribute to the atomic model? The Democritus atomic theory was improved and developed by other eminent philosophers. Some were the Greek philosopher Epicurus (341-270 BC) and the Roman Epicurean poet Lucretius (99-55 BC). ... In turn, Rutherford's experiments with alpha particles led him to conclude that atoms are mostly empty space, with a small, ... Ancient physics: How Democritus predicted the atom The idea of the atom goes as far back as the ancient Greek philosopher Democritus in about 400 B.C.E. This led to his "theory of eidôla" to explain how our minds create the illusion of ... Development of atomic theory Atom - Development, Theory, Structure: The concept of the atom that Western scientists accepted in broad outline from the 1600s until about 1900 originated with Greek philosophers in the 5th century bce. Their speculation about a hard, indivisible fundamental particle of nature was replaced slowly by a scientific theory supported by experiment and mathematical deduction. It was more than 2,000 ... Democritus Democritus (/ d ɪ ˈ m ɒ k r ɪ t ə s /, dim-OCK-rit-əs; Greek: Δημόκριτος, Dēmókritos, meaning "chosen of the people"; c. 460 - c. 370 BC) was an Ancient Greek pre-Socratic philosopher from Abdera, primarily remembered today for his formulation of an atomic theory of the universe. [2] Democritus wrote extensively on a wide variety of topics. [3] 2.1: Atoms One of the first people to propose "atoms" was a man known as Democritus. As an alternative to the beliefs of the Greek philosophers, he suggested that atomos, or atomon—tiny, indivisible, solid objects—make up all matter in the universe. Figure 2.1.1 2.1. 1 (Top) Democritus by Hendrick ter Brugghen, 1628. Democritus was known as the ... 4.2: Indivisible In chemical reactions, atoms are combined, separated, or rearranged. 4.2: Indivisible - The Atomic Theory is shared under a license and was authored, remixed, and/or curated by LibreTexts. You learned earlier how all matter in the universe is made out of tiny building blocks called atoms. All modern scientists accept the concept of the atom ... 3.2.1: Basic Atomic Theory From his experiments and observations, as well as the work from peers of his time, Dalton proposed a new theory of the atom (1803). This later became known as Dalton's atomic theory. The published (1808) tenets of this theory were as follows: All matter is composed of extremely small particles called atoms. Who Was Democritus? Democritus, ancient Greek philosopher who is credited with the birth of atomic theory. Credit: phil-fak.uni-duesseldorf.de Posted on December 11, 2015 July 27, 2016 by Matt Williams PDF Atomic Theory Timeline Atomic Theory Timeline Democritus ~450 BC John Dalton 1803 Michael Faraday 1839 J. J. Thomson 1896 Robert Millikan 1909 Ernest Rutherford ... particle) experiment *Most of an atom is empty space (p. 100-102) *1919- named positive charge the proton (+1) *1932- Rutherford and James Chadwick The History of the Atomic Model Democritus' Model. Democritus was an ancient philosopher who lived around 400 BC. He developed the first atomic model. Democritus asserted that matter is made up of very small particles that cannot be broken or divided. He called these particles atoms (atomos in Greek, which means indivisible). Atomic model In the years after Dalton described his atomic model, multiple experiments were performed that proved that charged particles exist. In 1897 English physicist J.J. Thomson discovered a negatively charged particle, which he called the electron.The existence of the electron showed that the 2,000-year-old conception of the atom as a homogeneous particle was wrong and that in fact the atom has a ... Development of the Atmoic Theory In this lesson, we will review the development of the atomic theory. One of the first atomic theorists was Democritus, a Greek philosopher who lived in the fifth century BC. Democritus knew that if a stone was divided in half, the two halves would have essentially the same properties as the whole.Therefore, he reasoned that if the stone were to ... John Dalton Birth date: September 6, 1766. Birth City: Eaglesfield. Birth Country: United Kingdom. Gender: Male. Best Known For: Chemist John Dalton is credited with pioneering modern atomic theory. He was ... Video: Democritus Atomic Model Democritus, a Greek philosopher who lived around 460 - 370 BCE, was a man of many ideas. His Atomic Theory, or Atomism, said that there had to be some sort of object that could not be broken ... Democritus Democritus was born in Abdera, around 460 B.C. Due to the fact that there was no technology, Democritus was unable to perform experiments; therefore, Democritus had no evidence of his theory, but it was proved to be somewhat close to what was discovered 2000 years later. ... Contribution to atomic theory "By convention bitter, by convention ... Understanding Atomic Models in Chemistry: Why Do Models Change? In the quest for understanding why atomic models change, we next consider the Bohr-Sommerfeld model of the atom presented in 1915-1916. Bohr's model of the atom provided an explanation of the paradoxical stability of the Rutherford model and spectra of hydrogen-like ions. UCSB Science Line Our understanding of the structure of the atom has vastly changed from the solid-ball model John Dalton first proposed with the development and advancement of quantum mechanics. It is the interplay between theory (e.g., quantum mechanics) and experiment that let's us characterize and engineer materials at the atomic level. Democritus' Idea of the Atom A: The modern kinetic theory of matter is remarkably similar to Democritus' ideas about the motion of atoms. According to this theory, atoms of matter are in constant random motion. This motion is greater in gases than in liquids, and it is greater in liquids than in solids. But even in solids, atoms are constantly vibrating in place. 5 Democritus Theory of Atoms 1. Democritus was not able to describe atomic model in detail. On his theory, Democritus only stated that atoms are in the solid form in the void sphare. We can not describe the internal structure of the atom itself. We now know that Atoms consist of 3 parts which are proton, neutron and electron. 2. essay homework paper phd project resume review speech study thesis