Be+ vs B+ Ionic Radii: Proton-Electron Ratio Analysis

[MathewsMD]

When competing the ionic radii of Be⁺ and B⁺, which is smaller? I understand there are periodic trends but there is an anomaly in ionization energies b/w B and Be since B has a lone 2p electron. So instead of looking at periodic trends directly, I assessed the proton-electron ratio and found for these cations, Be has a higher ratio (4/3 vs 5/4). This led me to believe Be⁺ has a smaller ionic radius compared to B⁺ since there is a stronger general attraction b/w the protons and electrons in this ion.

Any clarifications and comments on my thought process would be greatly appreciated!

 

[jbsteele]

Your thought process is correct. Beryllium (Be+) has a smaller ionic radius than Boron (B+), due to the higher proton-electron ratio in Be+. This anomaly in ionization energies between B and Be is due to the fact that B has a lone 2p electron, which is more difficult to remove than the 2s electron in Be.