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."

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.

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:He proposed, but did not prove

[Shipud]

Actually, by Rutherford's time the atomic theory was well established experimentally by Jean Perrin [nobel.se] 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).

Give Joseph Black his due credit!

[Richard Mills]

"200 years ago today (Oct. 21) John Dalton revolutionized chemistry by starting the process of turning it into an exact science"

Can't argue with John Dalton having helped revolutionize chemistry, but he didn't start the process of turning it into an exact science. I think that the credit for that probably belongs to British chemist Joseph Black, who founded calorimetry and was one of the first scientists to emphasize quantitative experiments. (Interestingly, at Edinburgh his chemistry chair was unsalaried!)

Re:Give Joseph Black his due credit!

[madmancarman]

There should also be some credit given to Henry Mosely [k12.il.us], 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.

Re:Only 200 Years?

[queen of everything]

Dalton (1766-1844) is widely regarded as the founder of the idea that all matter is made of tiny, indivisible particles called atoms. Although atoms were proposed 2500 years ago in ancient Greece, Dalton's work made them an indispensable part of chemical theory.
yes

Wait...

[__aaqgaf7843]

modern chemists don't measure molecular masses in daltons, they use gram/mole. Daltons aren't used until you get into larger molecules like proteins, as in "that protein is 70 kDa (kilodaltons) in size".

Ironically

[exp(pi*sqrt(163))]

When Dalton originally proposed his atomic theory there was much resistance. The idea of tiny, hard, indivisible units was unreasonable to many of the people around Dalton and it took a long time for people to accept his ideas. But guess what! The people who resisted were right. Today we have completely replaced the idea of an indivisible atom with a wavefunction in a Hilbert space. We might still call these things 'atoms' but they bear very little relationship with what Dalton was thinking of. In fact, at the time people used Dalton's theory as a metaphor as they couldn't take the ideas literally at all. And that's exactly what physicists do today.

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.

Re:And we're still teaching it wrongly

[VendingMenace]

And what is the right way, may i ask?

Really, there is no really good way to describe atoms. Sure you can say that QM is the way to go, but as someone else pointed out, the simplistic model of orbiting electrons works quite nice in may situations.

QM also has its failures. For instance, in calculating certain molecular orbital energies, using just a strict ionic resonance (the desciption that you would arrive at by just basic valence considerations) is much more accurate than the energy arrived at by adding into it covalent resonance character (what we get from QM considerations).

In the end, we just kinda use what seems to work best, quickest, or most with the least amount of work. That is the way of things. Sure we don't tell kids the earth in flat, but we don't really use the considerations of the curved earth everyday, do we? We say that we are "going over to our freinds house" not "going over and down, due to the cuvature of the earth, to our friends house." It would just be rediculous to say that. It is way more information than is needed in the cirmunstance.

By the same measure, it is not nessesary to underatnd QM, LCAO MO, SALC, Hartree Fock, or any of that other crap to understand that one Na combines with one Cl to make table salt now is it?

Most HS students will not really go on to use chemistry, they do not need to know QM to get by in the real world. And most of them will shy away from math. Perhaps this sounds bad, but really what we need to do is give them the best ahndle on chemistry possible. IN some cases this will mean making consetions and realizing that most people dont give a flying squirles rat's ass about chem, and teaching them acocurndingly.

In the end, if we can teach people enough chem so that they realize that some things are bad for them and others are good, then i think we have accounplished our job. If some of these people want to devote themseslves to years of esoteric research, then all the better, but we HAVE to reach the common man (boy) too.

Just my thoughts, perhaps a bit long, but i always get upset when people say "we are teaching inccorect stuff." Becuase, really, we are teaching stuff, that while perhaps not as accurate as possible, is stuff that really works in the real world.

Sorry if that sounded kinda bad, but really, what is wrong with working your way up conceptually, esp if the easier concepts work for 99.9% of the probelms the average person will encounter?