| A | B |
|---|
| James Chadwick | Responsible for discovering the neutron |
| John Dalton | Proposed first modern description of atom |
| J.J. Thomson | Discovered protons, electrons and isotopes |
| Democritus | Early Greek philosopher, believed matter was made up of small indivisible particles called "atomos" |
| Henry Moseley | Discovered that the properties of an element depend on the number of protons, said arrange periodic table by atomic number, not mass. |
| Neils Bohr | Created a workable description for hydrogen, unable to use successfully for all other elements |
| Aristotle | believed matter was continuous |
| Joseph Proust | Law of definite proportions |
| Antione Lavoisier | Law of conservation of mass |
| Amadeo Avogadro | Equal volumes of gas under identical conditions contain the same number of particles |
| J.L. Gay-Lussac | The ratio of the volumes of reacting gases is a constant |
| Marsden and Geiger | Conducted the gold foil experiment |
| Robert Millikan | Discovered the charge per electron |
| Ernest Rutherford | Proposed the existence of the nucleus and electron cloud |
| Niels Bohr | Proposed that electrons could exist at only certain energy levels |
