| A | B |
|---|
| atom | smallest unit of an element |
| nucleus | central region of an atom |
| electron | negatively charged particle in an atom |
| electron cloud | area around a nucleus containing electrons |
| plum-pudding model | T homson's idea of an atom |
| Democritus | Greek philosopher who named the atom |
| AMU | describes the mass of an atom |
| proton | positively charged particle in an atom |
| neutron | particle in the nucleus with no charge |
| atomic number | number of protons in an atom; identifies element |
| isotope | atom with a different number of neutrons |
| mass number | sum of the protons and neutrons in an atom |
| strong force | holds the nucleus together |
| weak force | allows a neutron to change to a proton or electron |
