Atomic radii of fluorine and neon in Angstrom $\left(\dot{\mathrm{A}}\right)$ units are respectively given by

In the periodic table the elements fluorine and neon have been observed in the second period.  The size of fluorine is smaller than the size of neon.  Because in a period from left to right the atomic size of an element gradually decreases.  Hence, the atomic radii of F and Ne are0.72Å and 1.60Å .

Even though from left to right the atomic radius decreases F has high electro negativity than Ne.