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Period: 500 BCE to
The Alchemists
Developed the theory that all metals are composed of mercury and sulfur, and it is possible to change base metals into gold. -
450 BCE
Aristotle
Aristotle did not believe in the atomic theory. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. -
442 BCE
Democritus
His theory stated that everything is composed of atoms, and that they are all physically invisible. -
427 BCE
Plato
Produced the theory that ideal geometric forms serve as atoms, and that atoms break down mathematically into triangles. -
Robert Boyle
Proposed the "Boyles Law" that states if the volume of a gas is decreased, the pressure increases proportionally. -
Period: to
Lavoisier
Lavoisier found that mass is conserved in a chemical reaction. -
John Dalton
His atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. -
Dmitri Mendeleev
He is known for his work on the Periodic Law and creation of the first Periodic table. -
The Curies
Pierre and Marie Curie discovered polonium and radium. -
J.J. Thompson
Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." -
Albert Einstein
His atomic theory says that any liquid is made up of molecules, and these molecules are always in random, ceaseless motion. -
Robert Millikan
His earliest major success was the determination of the charge carried by an electron, using the “falling-drop method. -
Ernest Rutherford
He postulated the nuclear structure of the atom, discovered alpha and beta rays, and proposed the laws of radioactive decay. -
Neils Bohr
He proposed the Solar System Model which stated that electrons revolve around the nucleus like planets revolving around the sun. -
Henry G.J. Thompson
He experimentally demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight. -
Werner Heisenberg
He contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly.
