| A | B |
|---|
| Atom | The smallest piece of an element that still represents the element |
| Electron | Atomic particle with a negative charge of -1 |
| Electron Cloud | Area around an atomic nucleus where an electron is most likely to be found |
| Neutron | Neutral particle in the nucleus of an atom |
| Nucleus | Small area in the center of an atom in which most of an atom's mass and the positive charge is concentrated |
| Proton | Atomic particle with a positive charge of +1. |
| Atomic Number | The number of protons in an atom of an element |
| Average Atomic Mass | Average mass of an element's isotopes, weighted according to the abundance of each isotope |
| Isotope | Any of two or more atoms of the same element that have different numbers of neutrons |
| Mass Number | Sum of the number of protons and neutrons in an atom |
| Nuclear Decay | Process that occurs when an unstable atomic nucleus changes into another more stable nucleus by emitting radiation. |
| Radioactive | Describes elements that spontaneously emit radiation |
| Spontaneous | Occurring without external force or cause |
