| A | B |
|---|
| Atom | the smallest piece of an element that still represents the element |
| electron | a particle with one negative charge |
| nucleus | most of an atom's mass and positive charge which is concentrated in a small area in the center of the atom |
| proton | atomic particle that has one positive charge |
| neutron | a neutral particle that exists in the nucleus of an atom |
| electron cloud | an area around an atomic nucleus where an electron is most likely to be located |
| atomic number | the number of protons in an atom of an element |
| Isotopes | are atoms of the same element that have a different number of neutrons |
| mass number | the sum of the number of protons and neutrons in an atom |
| average atomic mass | the average mass of the element's isotopes, weighted according to the abundance of each isotope |
| radioactive | elements that spontaneously emit radiation |
| nuclear decay | a process that occurs when an unstable atomic nucleus changes into another more stable nucleus by emitting radiation |
| ion | an atom that is no longer neutral because it has gained or lost electrons |
