Lanthanide contraction is a term used in chemistry to describe the greater than expected decrease in ionic radii of the elements in the lanthanide series from atomic number 58, cerium, to 71, lutetium, which results in smaller than otherwise expected ionic radii for the subsequent elements starting with 72, hafnium. The term was coined by the Norwegian geochemist Victor Goldschmidt in his series "Geochemische Verteilungsgesetze Der Elemente".
| Element | Ce | Pr | Nd | Pm | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Atomic electron configuration |
4f15d16s2 | 4f36s2 | 4f46s2 | 4f56s2 | 4f66s2 | 4f76s2 | 4f75d16s2 | 4f96s2 | 4f106s2 | 4f116s2 | 4f126s2 | 4f136s2 | 4f146s2 | 4f145d16s2 |
| Ln3+ electron configuration | 4f1 | 4f2 | 4f3 | 4f4 | 4f5 | 4f6 | 4f7 | 4f8 | 4f9 | 4f10 | 4f11 | 4f12 | 4f13 |
4f14 |
| Ln3+ radius (pm) (6-coordinate) | 102 | 99 | 98.3 | 97 | 95.8 | 94.7 | 93.8 | 92.3 | 91.2 | 90.1 | 89 | 88 | 86.8 | 86.1 |