| A | B |
|---|
| atomic number | the number of protons in the nucleus of an atom |
| electron | negatively charged particle in an atom. |
| proton | positively charged particle in an atom |
| neutron | particle in the nucleus of an atom with no charge |
| element | substance that cannot be broken down into simpler subtances |
| mass number | number of protons and neutrons in the nucleus of an atom |
| isotopes | atoms of the same element with differentnumbers of neutrons in their nuclei |
| nucleus | center part of an atom made up of protons and neutrons |
| half-life | the time it takes for half of the atoms of an element to decay |
| atomic mass | the average of all mass numbers for isotopes of an element |
| radioactive decay | release of nuclear particles and energy from nuclei |
| electron cloud | region surrounding the nucleus of an atom, where electrons are found |
| strong nuclear force | force which holds the nucleus of an atom together. |
