 | Term | Definition |
| |
Democritus |
Lived 460-370 BC |
| |
Democritus |
Greek Philosopher |
| |
Democritus |
Came up with "atom"; means "indivisible" |
| |
Democritus |
Ancient Greeks rejected his theory |
| |
John Dalton |
Worked in 1803 |
| |
John Dalton |
All matter is composed of atoms |
| |
John Dalton |
All atoms of a given element are identical in size, mass, and chemical properties. Atoms of a specific element are different from those of any other element. |
| |
John Dalton |
Atoms cannot be created, destroyed, or broken down into smaller particles. |
| |
John Dalton |
Different atoms combine in simple whole-number ratios to form compounds. |
| |
J.J. Thomson |
Worked in 1897 |
| |
J.J. Thomson |
Discovered electron |
| |
J.J. Thomson |
Determined charge-to-mass ratio of electrons |
| |
J.J. Thomson |
"Plum Pudding" model of atom |
| |
Robert Millakan |
Worked in 1909 |
| |
Robert Millakan |
"Oil Drop" experiment |
| |
Robert Millakan |
Calculated the mass of an electron (-9.1*20^-28g) |
| |
Ernest Rutherford |
Worked in 1911 |
| |
Ernest Rutherford |
Discovered proton and nucleus |
| |
Ernest Rutherford |
Determined that atoms are mostly empty space |
| |
Ernest Rutherford |
Performed "Gold Foil" experiment to see if atoms in gold deflected atoms of alpha particles. A few were deflected or bounced back, but most passed through. Proved that there were positive charges in atoms. |
| |
Neils Bohr |
Worked in 1913 |
| |
Neils Bohr |
Created planetary (Bohr) model of the atom |
| |
Neils Bohr |
Said that electrons move in specific circular orbits around the nucleus, based on their energy levels. |
| |
James Chadwick |
Worked in 1932 |
| |
James Chadwick |
Discovered neutron |
| |
James Chadwick |
Developed electron cloud model of atom |
