Europium has 63 electrons arranged as 2, 8, 18, 25, 8, 2 across 6 shells, which is why it sits in period 6.
Start from the previous noble gas core, written in square brackets, then add the remaining electrons in filling order. For europium that gives [Xe] 4f7 6s2.
| Atomic number | 63 |
| Symbol | Eu |
| Atomic mass | 151.96 u |
| Group | f-block (no group number) |
| Period | 6 |
| Block | f-block |
| Category | Lanthanide |