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350
Aristotle
350 B.C.
Aristotle, Greece - claimed that there was no smallest part of matter and that different substances were made up of proportions of fire, air, earth, and water. As there were of course no experimental means available to test either view, Aristotle's prevailed mainly because people liked his philosophy better. -
400
Democritus
400 B.C.
Democritus, Greece - stated that all matter is made up of atoms. He also stated that atoms are eternal and invisible and so small that they can’t be divided, and they entirely fill up the space they’re in. -
Antoine Lavoisier
Lavoisier (1777), France - provided the formula for the conservation of matter in chemical reactions, and also distinguished between an element and a compound. -
John Dalton
Dalton thought it was just a sphere, -
James Maxwell
James Clerk Maxwell's principal contribution to the atomic concept had to do with his theory of electromagnetism. -
JJ Thomson
J.J Thomson England - discovered the electron and developed the plum-pudding model of the atom. -
Marie Curie
The Curies (1898), France - discovered radium and polonium when they started to investigate radioactive substances -
Max Planck
Max Planck (1900), Germany - originated the quantum theory -
Robert Milikan
Robert Millikan (1908), USA - found out the electric charge of the electron -
Ernst Rutherford
Ernest Rutherford (1909), England - used the results of his gold-foil experiment to state that all the mass of an atom were in a small positively-charged ball at the center of the atom. -
Neils Bohr
Neils Bohr (1913), Denmark - stated that the electrons moved around the nucleus in successively large orbits. He also presented the Bohr atomic model which stated that atoms absorb or emit radiation only when the electrons abruptly jump between allowed, or stationary, states. -
Henry Moseley
Henry Moseley proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. -
Erwim Schrodinger
Erwin Shroedinger (1926), Austria - introduced the Shroedinger Equation, a wave equation that describes the form of the probability waves that govern the motion of small particles and how these waves are altered by external influences. -
Werner Heisenberg
Werner Heisenberg worked out that particles had a lot more energy over short distances than expected. He realized that a particle can borrow energy as long as it is paid back in a short time. The relationship he came up with was the position and energy of a particle can only be known to a certain amount. This is known as the uncertainty principle.This is believed to be the way a particle escapethe charge at the nucleus of an atom and is the mechanics of radioactive decay. -
James Chadwick
Chadwick (1931), England - discovered the neutrally-charged neutron. -
Modern Atomic Theory
This is what we think an atom looks like in todays time.
