Meitnerium has 109 electrons arranged as 2, 8, 18, 32, 32, 15, 2 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 meitnerium that gives [Rn] 5f14 6d7 7s2.
| Atomic number | 109 |
| Symbol | Mt |
| Atomic mass | 278 u |
| Group | 9 |
| Period | 7 |
| Block | d-block |
| Category | Transition metal |