| A | B |
|---|
| atom | the smallest particle into which an element can be divided and still be the same substance |
| Democritus | Greek man who said that atoms were small, hard particles that could not be divided anymore |
| John Dalton | said atoms join with other atoms to make new substances- thought atoms were solid balls |
| J.J. Thomson | discovered the electron and developed his "plum pudding" model |
| electron | a subatomic particle with a negative charge |
| Rutherford | through gold foil experiment, discovered the nucleus and protons |
| nucleus | the atom's central region made up of protons and neutrons |
| proton | subatomic particle with a positive charge found in the nucleus |
| electron cloud | a region around the nucleus of an atom where electrons are likely to be found - current model |
| Niels Bohr | discovered electrons move in specific paths called energy levels |
| atomic mass unit | a unit of mass that describes the mass of an atom or molecule |
| neutron | a subatomic particle that has no charge found in the nucleus of an atom |
| neutral atom | when the atom has no charge - protons and electrons are equal |
| ion | charged atom that has an unequal number of protons and electrons |
| atomic number | the number of protons in the nucleus of an atom- identifies the element |
| isotopes | atoms that have the same number of protons but have different numbers of neutrons |
| mass number | the sum of protons and neutrons in the nucleus of an atom |
| atomic mass | the mass of an atom expressed in atomic mass units |
| gravitational force | force that acts between all objects - very small in atoms |
| electromagnetic force | force that holds electrons around the nucleus by opposite forces attracting |
| strong force | keeps nucleus together - stronger than electromagnetic force |
