| A | B |
|---|
| Nucleus | A dense, positively charged mass located in the center of the atom. |
| Proton | A positively charged subatomic particle that is found in the nucleus of an atom. |
| Electron | Negatively charged subatomic particle that is found in the space outside the nucleus. |
| Neutron | Neutral subatomic particle that is found in the nucleus of an atom. |
| Atomic Number | Equals the number of protons in an atom of an element. |
| Mass Number | Sum of the protons and neutrons in the nucleus of an atom. |
| Isotope | Atoms of the same element that have different numbers of neutrons and different mass numbers. |
| Energy Level | Possible energies that electrons in an atom can have. |
| Electron Cloud | A visual model of the most likely location for electrons in an atom. |
| Orbital | A region of space around the nucleus where an electron is likely to be found. |
| Ground State | When all electrons in an atom have the lowest possible energies. |
