| A | B |
|---|
| element | a substance that cannot be broken down into simpler substances |
| electron | negatively charged particles that surround the nucleus of an atom |
| proton | positively charged particles found in the nucleus of an atom |
| neutron | particle found in the nucleus of an atom that had no charge |
| electron cloud | region surrounding the nucleus that contains the electrons |
| atomic number | number of protons in the nucleus of an atom |
| isotopes | atoms of the same element with a different number of neutrons |
| mass number | is the number of protons and neutrons in the nucleus of an atom |
| radioactive decay | the release of nuclear particles and energy |
| half-life | the amount of time required for half of a sample of an element to decay |
