Atomic and Ionic Radii

Both the covalent radius and the ionic radius (measured in a given oxidation state) grow larger on descending Group 15, as expected from the addition of successive electron shells. The increase, however, is not uniform across the group. Going from nitrogen to phosphorus the covalent radius jumps up considerably, since an entirely new principal quantum shell is being added. From arsenic to bismuth, on the other hand, the radius grows only modestly — because the intervening $d$ orbitals (and, for bismuth, the $f$ orbitals too) are now completely filled, and their poor shieldin …