| A | B |
|---|
| Electron configuration | Electron configuration is the arrangement of electrons in atoms. |
| Aufbau principle | According to the Aufbau ('building up' in German) principle, an electron occupies the lowest-energy orbital that can receive it. |
| Hund's Rule | According to Hun's rule, orbitals of equal energy are each occupied by one electron before any one orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin. |
| Pauli exclusion principle | According to the Pauli exclusion principle, no two electrons in the same atom can have the same set of four quantum numbers. |
| highest occupied energy level | The highest occupied energy level is the electron-containing main energy level with the highest princeipal quantum number. |
| inner-shell electrons | Inner-shell electrons are electrons not in the highest occupied energy level. |
| noble gases | The Group 18 elements (helium, neon, argon, drypton, xenon, and radon) are called the noble gases. |
| noble gas configuration | A noble gas configuration is an outer main energy level fully occupied, in most cases, by eight electrons. |
