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What is Atomic Theory?

Atomic theory states that all matter is made up of tiny atoms.
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  • Written By: Michael Anissimov
  • Edited By: Bronwyn Harris
  • Last Modified Date: 19 October 2014
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Atomic theory is the idea that matter is made up of little units called atoms. When the ancient Greek philosopher Democritus came up with the idea in the 5th century BC, is was originally meant to refer to indivisible units. As of 1897, the British scientist J.J. Thomson discovered that atoms are in fact made up of smaller particles. Today, this theory refers to matter being made up of units that are indivisible only some of the time. Exceptions include plasmas, such as fire, other ionic arrangements, such as those found in the body, radioactive materials, and many more.

Even though atomic theory today is a familiar cornerstone of modern science, like germ theory or evolution, throughout most of human history, people believed that matter was probably continuous and could be broken down into arbitrarily small quantities. It wasn't until 1803, or possibly a bit before, that the English chemist John Dalton revived the old idea and used it to solve various problems that chemists were grappling with at the time. Rather than any one experiment leading to the idea, it emerged from analysis of multiple experiments involving the properties of gases and chemical reactions. His theory was popularized and confirmed experimentally over the course of the early 19th century.

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Dalton's atomic theory had five main points:

Most of the above is still accepted by scientists today, except for a few points. First, the discovery of nuclear fusion/fission and radioactivity prompted revision of point #2. Isotopes prove that atoms of the same element can actually have small differences due to a different number of neutrons. Also, the existence of ions with varying numbers of electrons also contradicts this point.

The fifth point is also invalidated by nuclear physics, since atoms can indeed by destroyed in nuclear chain reactions. The second item of point #4 is also quite incorrect, as, for instance, water is H2O, not HO. His insistence that atoms combine in equal amounts to create compounds held back acceptance of his theory for years. Regardless, from the viewpoint of today, Dalton contributed remarkably for his time, and his name continues to be revered by its association with the theory.

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Fa5t3r
Post 57

@pastanaga - The idea that atoms are the smallest building blocks in creation is definitely not taken for granted, and in fact, they have discovered many other particle types which are smaller than atoms (although I don't think they make up atoms, they just exist alongside them).

I don't really understand physics when it gets that theoretical though, it seems to get very complicated and slightly wishy-washy but I'm sure it makes sense to those who are studying it.

pastanaga
Post 56

I think it's interesting to speculate that we may still have not found the lower limit of size for matter. Atoms might be made up of even smaller particles, there's no reason why they can't be.

I guess I kind of like the idea that size differences can go on forever, getting smaller and smaller or bigger and bigger so that space is infinite in more directions than we might think.

KoiwiGal
Post 55

@anon112649 - Unfortunately a lot of the time science history tends to be a bit Western-centric, probably because when it is in English it's being written by a Westerner who might not know about other theories.

In this case though, I think it's talking about a specific kind of modern atomic theory, which is attributed to a particular person. If they were talking about the history of atoms in science, they'd have to mention a lot of other people, since the idea of tiny particles has been around for a while in both the East and the West.

anon319327
Post 54

What about Bohr? What part did he have in it?

anon312838
Post 52

Were there any problems with this theory?

anon244370
Post 43

Name five areas where the atomic theory is used.

anon158126
Post 37

What about the second point, though?

"2) All atoms of a given element have are identical to each other."

Aren't isotopes the same given element but different amount of nuclei? More neutrons?

anon149821
Post 36

What a delightfully succinct post.

anon142322
Post 33

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Post 32

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Post 30

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anon112649
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anon104419
Post 18

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anon97548
Post 17

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Post 16

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anon67948
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Post 7

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