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Jan 1, 1000
Aristotle 500 BC
One of the first models of the atom. Aristotle thought that everything was made from the four elements. -
Jan 1, 1000
Democritus 500 BC
Democritus believed that everything could be divided until it reached its smallest point, which he called atoms. -
John Dalton
John Dalton discovered colorblindness and said that every element as made up of different atoms, each atom having different masses. He also said compounds were made of atoms from different elements. His idea of an atom was a billiard ball, round and hard. -
JJ Thomson
Thomson created an experiment with a cathode ray tube that showed that the deflection of rays by magnets showed a particle that is smaller than an atom. He called it the electron. He made a model of an atom, which he called the plum pudding model. -
Henri Becquerel
Becquerel discovered that the rays that are emitted from uranium are different from x-rays. He also found out that the rays from uranium cannot be detected by eletrical or magnetic fields. -
Marie and Pierre Curie
Marie Curie discovered radioactivity with Henri Becquerel. -
Robert Millikan
Millikan found out how to find the mass of an electron by using the oil drop experiment. -
Ernest Rutherford
Ernest Rutherford proved that the plum pudding model was not accurate by shooting alpha rays at gold foil. Some rays went through the foil while others bounced back or shot in other directions. He then came up with the planetary model. -
Niels Bohr
Bohr discovered how to calculate energy levels by applying the quantum theory to Rutherford's planetary model. -
James Chadwick
Chadwick discovered the neutron, which eventually led to the creation of the atomic bomb.
