Happy Birthday, Atom

Shipud writes "200 years ago today (Oct. 21) John Dalton revolutionized chemistry by starting the process of turning it into an exact science. He presented the Table of Atomic Weights, at the Manchester literary and Philosophical Society. Dalton's work proposed atoms exist: and not just as an explanatory or philosophical tool. His theory laid the foundations for the periodic table of the elements (1869, Mendeleev), and indeed to all modern chemistry. The molecular weight of compounds is today measured in Daltons, the weight of a hydrogen atom. Read more about Mr. Dalton in today's Nature: a man of many interests, whose atomic theory preceded experimental evidence by a century. Read also about Daltonism -- and why it is named after him."

Comments

He proposed, but did not prove

[rev063]

Dalton proposed the existence of the atom, but it took Rutherford to verify its structure and prove it existed as Dalton suggested.

Re:He proposed, but did not prove

[Shipud]

Actually, by Rutherford's time the atomic theory was well established experimentally by Jean Perrin Rutherford contributed to the nuclear theory of the atom (i.e. that it is composed of a nucleus which holds most of teh atom's mass and orbiting electrons of opposite charges).

Daltons

[friendofafriend]

Actually, isn't a dalton 1/12th the mass of a C12 atom? While very close to the mass of H1, they are not identical.

Re:Give Joseph Black his due credit!

[madmancarman]

There should also be some credit given to Henry Mosely, the British scientist who arranged the periodic table not only by chemical properties, but by atomic number (number of protons) as well.

Unfortunately for Mosely, he was volunteered for the British army in World War I and was killed in action when he was 27.

Perrin didn't get experimental evidence

[siskbc]

Actually, by Rutherford's time the atomic theory was well established experimentally by Jean Perrin Rutherford contributed to the nuclear theory of the atom (i.e. that it is composed of a nucleus which holds most of the atom's mass and orbiting electrons of opposite charges).

Not really. Perrin did work complementary to that of Thomson regarding the negative nature of part of the atom (ie, cathode rays). He also *proposed* a solar-system model for the atom in 1901, but wasn't able to substantiate this. Later, he did some work on Brownian motion, and that's what he got the prize for (as mentioned in your link, actually). But he didn't get any experimental evidence for the heavy nucleus surrounded by a very undense region. Rutherford did, in 1909, with his alpha-particle backscattering experiment. Without that experiment, which was certainly not redundant, it's hard to imagine how established atomic theory could possibly have been.

Really, atomic theory wasn't well established at least until Millikan did his oil-drop experiment, establishing the charge/mass ratio of the electron, and by deduction, the proton as well.

200 years old? Try 2400.

[espo812]

I just had a western civilization exam today. So to make up for my poor score on the test itself, I will attempt to impart something I actually did learn in the class (that was not tested). To quote my text:

[...] the philosopher Democritus (b. ca. 460 B.C.) [...] concluded that all things consisted of tiny, indivisible particles, which could be arranged and rearranged in an infinate variety of configurations. He called these particles atoma, "the uncuttable" (from which the word atom is derived).

So, this puts the atom at abount 2400 years old.