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400 BCE
Democritus
The first person who used the term atom. He thought that if you took a piece of matter and divided it and continued to divide it you will eventually come to a point where you can't divide it anymore. -
340 BCE
Aristotle
He thought that all materials on Earth were not made of atoms, but made up of the 4 elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. -
Evangelista Torrice
He suggested that the atmosphere could push mercury up a tube. Today, his apparatus is known as a barometer. -
Antoine Lavoisier
He came up with the conservation of mass. States that in an isolated system is neither created nor destroyed by chemical reactions or physical transformations. -
John Dalton
Was the first to adopt Democritus' theory into the first modern atomic model. In his theory he said that chemical elements are made of atoms. the atoms of an element are identical in their masses, atoms of different elements have different masses, atoms only combine in small, whole number ratios such as 1:1 1:2 2:3 ect, and atoms can be neither created nor destroyed. -
Ernest Rutherford
Set up his now famous gold foil experiment. Most particles did not deflect at all. He said that there must be a positive center of the foil which he called the nucleus -
J.J. Thomson
Credited for discovering the electron. His experiment showed that all atoms contain negatively charged subatomic particles or electrons. -
Robert Millikan
Had an accurate determination of the charged carried by an electron, he used the "falling-drop method". He proved that his quanity was a constant for all electrons -
Niels Bohr
He proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. -
Erwin Schrodinger
He used Heisenberg's uncertainty principle to come up with the model that we still use today. The type of probability orbit is dependent on the energy level described by Bohr. -
Louis De Broglie
Best known for predicting the wave nature of electrons/ Experiments had indicated that the electron must more around a nucleus and that there are restrictions on its motion. -
James Chadwick
Bombarded beryllium atoms with alpha particles and produced an unknown radiation. This particle became known as the neutron.
