Atomic radii of F and Ne (in $\stackrel{\mathrm{o}}{\mathrm{A}}$) are given by :

Atomic radius decreases in a period from left to right, hence fluorine has a very less atomic radius (covalent atomic radius = 0.72 $\stackrel{\mathrm{o}}{\mathrm{A}}$).
But inert gases (like Ne) are monoatomic gases, hence their covalent atomic radius cannot be found. In fact, their calculated atomic radius is the van der Waals' radius, which is found almost double to covalent radius, hence the van der Waals' radius of neon (Ne) is about 1.60 $\stackrel{\mathrm{o}}{\mathrm{A}}$.