Who discovered the atom?
Name: jessica a gancarski
Who discovered the atom?
A simple question, but deceptively complicated.
What does it mean to "discover" something?
The first person to propose that matter was made
of atoms, and then write it down, was a Greek philosopher
named Democritus. But he had no experimental proof of his
notion. Then, a number of scientists, starting probably with Newton in
the late 1600s, proposed a corpuscular, or atomic, model. But it
wasn't until the late 1700s/early 1800s that John Dalton proposed
that all matter was made of atoms and actually used it to explain
a bunch of experiments that had been done on gases, and to calculate
atomic weights of elements. However, he still hadn't PROVED that
atoms existed...he just showed that the atomic concept was useful
and helped explain a lot of data. Probably the best direct probe
of the atom was first done by Rutherford and his student, C.T.R. Wilson,
who invented the cloud chamber and used it to show that when thin
gold foil is bombarded by helium nuclei (alpha particles), the particles
are occasionally deflected by a very large angle, but usually pass
straight through. This gave rise to the realization that the gold
was composed of atoms, with a tiny nucleus at the middle which
could occasionally collide with an alpha particle and send it flying.
Coupla more comments for ya. I think the Greek concept of the atom was
unlike ours: to their minds a pickle was composed of small green sour
atoms, a fire of hot light bright atoms, etc. More of an aesthetic
than empirical concept. In my opinion they get a little more credit in
general for atoms than they deserve. Second, in addition to Dalton's work
suggesting the atom because of fixed chemical combining rules, there was
the astoundingly successful kinetic theory of gases, a subject of intense
interest in the nineteenth century, which relies utterly on gases being
made of little bits of flying matter. Names here are Bernoulli (1740s),
Joule (1850s), Clausius & Maxwell (1860s), and finally the giant Boltzmann
(1870s). Even as late as 1900 the existence of atoms was seriously doubted
by able scientists (e.g. Mach), and from the point of view of many the
definitive proof is the apparently unique explanation by Einstein in 1905
of "Brownian motion," the incessant jiggling of pollen grains visible under
a microscope that is caused by its battering by the invisible molecules.
The experiment in 1909 by Geiger and Marsden in the laboratory of
Rutherford (alpha particle scattering from gold foil) is usually considered
proof of the existence of the nucleus, although of course a nucleus implies
an atom too.
It should however be pointed out that most scientists utterly
rejected the kinetic theory of gases, and that the reputations
of all the aforementioned scientists were damaged severely in the
eyes of their contemporaries by their espousal of atomic theories.
Boltzmann in particular took the rejection of his work particularly
hard...in fact, he killed himself. Too bad he didn't wait around
a bit longer.
I think that you could argue that the early spectroscopic work
of Angstrom, Balmer, etc. provided proof of the existence of
atoms, although the experiments may not have been properly interpreted
at the time. In hindsight, they were probing atomic energy levels.
Finally, although the Greek view of "atoms" was certainly not
the same as the idea we have today, certainly that particular
school was the first to put forth the idea that the microscopic
properties give rise to macroscopic properties. Sure, they got the
details all wrong, and worked without experimental data.
In retrospect, it was a lucky guess. But science is full of
lucky guesses, and in my opinion it does no harm to give
Democritus credit for his cleverness. Especially since almost
noone believed him at the time....often a good sign that one is
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Update: June 2012