Question

In the ionic compound KF, the $K^{+}$ and $F^{-}$ ions are found to have practically identical radii, about $1.34\AA$ each. What do you predict about the relative atomic radii of K & F?

Answer 1

The $K^+$ and $F^-$ have the identical ionic radii in the ionic compound KF about 1.34 Angstrom.

Atomic radii of both $K^+$ and $F^-$ are different even though they have the same ionic radii.

If Potassium loses an electron, the outermost electron orbit is gone and so the atomic radius reduces, therefore when $K^+$ electron gains an electron, its atomic radius increases.

If fluorine gains an electron, atomic radius increases due to more electrons, therefore Fluorine loses an electron $F^-$, its atomic radius decreases.