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465 BCE
Democritus
He determined that atoms cannot be divided and that matter is made up of mostly empty space through which atoms move. -
340 BCE
Aristotle
He disagreed with the atomic theory and believed that air, earth,water, fire and aether made up all matter -
Evangelista Torricelli
He discovered that air has weight and can push mercury up a column. -
Antoine Lavoisier
He found that mass is conserved in a chemical reaction. This is known as the law of conservation of matter. -
John Dalton
He found that all matter is composed of atoms, atoms cannot be created nor destroyed, all atoms of the same element are identical, chemical reactions occur when atoms are rearranged and that compounds are formed by the combination of two or more different atoms. -
J.J. Thompson
He discovered that all cathode rays are composed of identical negatively charged particles which were later called electrons. This is know as the "plum pudding model". -
Robert Millikan
He found that the mass of an electron is very small for such a large charge. -
Earnest Rutherford
He shot alpha particles at gold foil and found that some bounced back. He concluded that the nucleus was dense. -
Niels Bohr
He developed an explanation of the atomic structure and his model shows a small positively charged nucleus surrounding orbiting electrons. -
Louis De Broglie
He discovered the wave nature of electrons and suggested that all matter has wave properties. -
Erwin Schrodinger
He described the likelihood of discovering an electron in a certain position by using equations. This model is known as the quantum mechanical model of the atom. -
James Chadwick
He discovered the neutron and that it has no electrical charge.