Hi Arkadiy,

In general, the more electrons present, the more chances there will be for an atom to exhibit temporary dipole moments, resulting in higher london dispersion force.

Since fluorine is so small and has very little electrons, plus its electrons are so tightly held due to its high electronegativity, its going to have a low london dispersion force. This actually explains why we find F2 to be in gaseous phase while I2 exists in solid phase. A stronger intermolecular force allows for the compound to be better connected to one another and stay in solid phase, while weak intermolecular forces means that molecules of the same compound does not adhere as easily with each other, and will generally favour gaseous forms.

I hope that that helps. Let me know if you have any more questions!

Cheers and happy studying,

Molly