The effective charge on the 5s and 5p electrons of La³⁺ is 11.25, and the radius of La³⁺ is 103.2…

The effective charge on the 5s and 5p electrons of $\text{La}^{3+}$ is $11.25$, and the radius of $\text{La}^{3+}$ is $103.2\ \text{pm}$. Each lanthanoid adds one proton and one 4f electron, and the 4f electron cancels $0.85$ of the proton's charge. Use the model to find the effective charge and the radius of $\text{Gd}^{3+}$ (atomic number 64). By how many picometres does your radius differ from the measured $93.8\ \text{pm}$?