| A | B |
|---|
| atoms | the smallest particle to which an element can be divided and still be the same substance |
| electrons | subatomic particles that have a negative charge |
| nucleus | an atom's central region, which is made of protons and neutrons |
| electron cloud | a region around the nucleus of an atom where electrons are likely to be found |
| Democritus | Greek Philosopher who first used the term "atom" |
| John Dalton | published his atomic theory in 1803 |
| J.J. Thomson | experimented with a cathode ray tube to discover electrons |
| Rutherford | connected with the "shooting gallery" experiments known as gold-foil experiments |
| proton | a subatomic particle that has a positive charge and that is found in the nucleus of an atom |
| atomic mass unit | a unit of mass that describes the mass of an atom or molecule |
| neutron | a subatomic particle that has no charge and is found in the nucleus of an atom |
| ion | a charged particle |
| atomic number | the number of protons in the nucleus of an atom; the same for all atoms of an element |
| isotope | an atom that has the same number of protons as other atoms of the same element, but has a different amount of neutrons which changes its atomic mass |
| mass number | the sum of the number of protons and neutrons in the nucleus of an atom |
| atomic mass | the mass of an atom expressed in amu's |
| gravitational force | a small force within an atom; this force acts between all objects at all times |
| electromagnetic force | force that holds the electrons around a nucleus |
| strong force | holds the nucleus together |
| weak force | found in radioactive atoms; allows neutrons to change in an unstable atom |
