Dysprosium has 66 electrons arranged as 2, 8, 18, 28, 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 dysprosium that gives [Xe] 4f10 6s2.
| Atomic number | 66 |
| Symbol | Dy |
| Atomic mass | 162.50 u |
| Group | f-block (no group number) |
| Period | 6 |
| Block | f-block |
| Category | Lanthanide |