How do the ionic radii of lanthanum and lutetium compare?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A line graph showing electron probability distributions for gadolinium, with separate curves for 4f, 5s, 5p, 5d, and 6s orbitals. The x-axis shows distance from the nucleus in atomic units and the y-axis shows probability P2(r). — rare-earth element Electron probabilities, P²*(r)*, for the 4f, 5s, 5p, 5d, and 6s electrons of gadolinium.

The ionic radii of lanthanum and lutetium exhibit a steady decrease due to a phenomenon known as the lanthanide contraction. This effect occurs because the 4f electrons added across the series provide imperfect shielding of the increasing nuclear charge, which draws the electrons closer to the nucleus.12

As a result, the ionic radius of the trivalent lanthanum ion (La $^{3 +}$ ) is larger than that of the heavier trivalent lutetium ion (Lu $^{3 +}$ ). According to data for the R $^{3 +}$ ion, the radius of lanthanum is 1.045 Å, while the radius of lutetium is 0.861 Å.2