Question

The single-bonded metallic radius of sodium is $157$ pm. Assume that the increment between radii of different magnitudes is $60$ pm. The covalent radius of Na in pm is $(90+x)$. Find $x$.

Answer 1

The valence electrons are mobile and weakly attracted. However, the metallic forces are weaker than covalent forces. Hence, the metallic radius is larger than the covalent radius. The single-bonded metallic radius of sodium is 157 pm.
The increment between radii of different magnitudes is 60 pm.

The covalent radius of Na in pm is $157pm-60pm=97pm$.

$\therefore 90+x=97pm\Rightarrow x=7pm$