Oganesson has 118 electrons arranged as 2, 8, 18, 32, 32, 18, 8 across 7 shells, which is why it sits in period 7.
Elements this heavy last for only a moment, so this configuration is predicted from theory rather than measured.
Start from the previous noble gas core, written in square brackets, then add the remaining electrons in filling order. For oganesson that gives [Rn] 5f14 6d10 7s2 7p6.
| Atomic number | 118 |
| Symbol | Og |
| Atomic mass | 294 u |
| Group | 18 |
| Period | 7 |
| Block | p-block |
| Category | Noble gas |
| Valence electrons | 8 |
| Element | Configuration |
|---|---|
| Helium | 1s2 |
| Neon | [He] 2s2 2p6 |
| Argon | [Ne] 3s2 3p6 |
| Krypton | [Ar] 3d10 4s2 4p6 |
| Xenon | [Kr] 4d10 5s2 5p6 |
| Radon | [Xe] 4f14 5d10 6s2 6p6 |
Elements in the same group have the same number of outer electrons, which is why they behave alike.