-
440 BCE
Plato
He said that matter was "continuous" or always present. -
400 BCE
Democritus
Suggested that all matter was made of tiny particles that determined the property of the matter -
500
The Alchemists
They thought that sulfur and mercury made up all metals. They paved the way of experimenting about the atomic theory by believing in a set list of laws about the universe. -
Robert Boyle
He supported atomism (the belief that matter is made up of small particles) and experimented on existing elements in an attempt to prove it. He also proved oxygen's existence. -
Antoine Lavoiser
He grouped the elements as simple substances, metals, non-metals, and earthly substances. -
John Dalton
Said that all matter is made up of atoms; atoms of certain elements are identical; and that elements/matter cannot be destroyed. -
Amadeo Avogadro
Said that equal volumes of gas that are at the exact same temperature and pressure have the same amount of molecules despite their different properties -
Dmitri Mendeleev
Made a periodic table with spaces for elements that had not been discovered yet -
JJ Thompson
Discovered that atoms consisted of smaller components -
Marie & Pierre Curie
Said that rays given off by radium and polonium were caused by atoms disintegrating inside the elements -
Albert Einstien
Proved the existence of atoms -
Robert Millikan
Discovered the charge of an atom and learned that electrons all had the same negative charge -
Ernest Rutherford
Said that atoms had a positively charged core called a nucleus and that electrons with a negative charge circled the nucleus -
Henry G. J. Mosely
Mosely's Law: Frequencies are proportional to the squares of whole numbers that are equal to the atomic number and a constant. -
Neils Bohr
Said that electrons move around the nucleus in a prescribed orbit and when electrons jump from the orbit, they cause radiation -
James Chadwick
Proved the existence of the neutron, a part of the nucleus with neutral charge