| A | B |
|---|
| Atom | The smallest particle of an element. |
| Nucleus | Dense, positively charged mass at the center of an atom. |
| Proton | Positively charged subatomic particle found in the nucleus. |
| Neutron | Neutral subatomic particle found in the nucleus. |
| Electron | Negatively charged subatomic particle found outside the nucleus. |
| Mass number | The sum of the protons and neutrons in the nucleus of an atom. |
| Atomic number | This number identifies the element and is equal to the number of protons found in the nucleus. |
| Ion | An atom with a charge (unequal number of protons and electrons) |
| Isotopes | Versions of the same element with different numbers of neutrons. |
| Energy levels | The possible energies that an electron in an atom can have. |
| Atomic Weight/Mass | The weighted average mass of all of an element's isotopes' mass numbers (usually a decimal). |
| Electron Cloud | A visual model showing the most likely locations for the electrons in an atom. |
| Electron configuration | The arrangement of electrons around the nucleus of an atom. |
| Ground state | When all of the electrons in an atom have their lowest possible energies. |
