Why is the atomic radius of Boron smaller than that of Be?

[mahela007]

The 1st ionization energy decreases from Be to B. This would suggest that the outermost electron is held more loosely in B. Also, considering the electron configurations of Be (1s² 2s²) and B (1s² 2s² 2p¹) one would think that in B, the shielding effect of the 2s electrons on the p electron would also act to increase the atomic radius...
but alas that isn't how it is... Now.. the universal question: WHY?

 

[Bob_for_short]

Because the configuration (1s² 2s²) in B is smaller in size due to higher nucleus charge, no?

 

[mahela007]

Wait.. i think I made a mistake in my initial post.
What I meant to ask was why is the atomic radius of B smaller when it has an extra P orbital which is also shielded by full 1s and 2s orbitals?

 

[Bob_for_short]

Wait.. i think I made a mistake in my initial post.
What I meant to ask was why is the atomic radius of B smaller when it has an extra P orbital which is also shielded by full 1s and 2s orbitals?

Ion B⁺ radius is smaller than that of neutral Be despite the same electron configuration 1s² 2s² just because the charge of nucleus in B is higher. The rest is a collective electronic effect, I think.

Besides, a p-state is not spherical. Which axe (dimension) is considered as the B-size?