-
Period: 460 BCE to 370 BCE
Democritus
influential Ancient Greek philosopher that is remembered today for his formulation of the atomic theory, first to use "atomos" the smallest particle of matter that cannot be divided -
Period: 384 BCE to 322 BCE
Aristole
He believed in four elements air, earth, water, fire. He felt that regardless of the number of times you cut a form of matter in half, you would always have a smaller piece of matter -
Period: to
Antoine Lavoisier
Law of Conservation of Mass-- which states mass cannot be created or destroyed. He said the mass of reactants will equal mass of products. -
Period: to
Joseph Proust
Discovered Law of Definite Proportions-- a chemical compound contains the same elements in exactly the same proportions by mass -
Period: to
John Dalton
English Chemist/Schoolteacher. Discovered the Law of multiple proportions-- if compounds are composed of the same elements, the masses of the elements can be expressed as ratios of whole numbers. -
Period: to
JJ Thomson
Figured out that electrons had a negative charge with the Cathod Ray Tube. -
Period: to
Robert Milikan
oil drop experiment. figured out the mass of electrons -
Period: to
Ernest Rutherford
Gold Foil Experiment. Discovered nucleus was very small and very dense. Also, discovered a proton was a positive charge. -
Period: to
Niels Bohr
Danish physicist who worked with Rutherford. Theory explained how the electrons moved around the nucleus. Electrons moving around nucleus can only follow certain orbits. -
Period: to
James Chadwick
English physicist who worked with Rutherford. He discovered the neutron