The bond length in f2 is 1.417 å, instead of twice the atomic radius of f, which is 1.28 å. what can account for the unexpected length of the fuf bond?

The bond length is the distance between the centers of the two atoms in a bond. Fluorine gas is diatomic in nature. When two fluorine atoms are bonded, the bond length is longer than twice the atomic radius of the fluorine atom. This is brought about by the repulsion forces between two like atoms. Hence, the distance would be longer.

Yes it would be a physical change.