# Why Br2 with Br2 has higher viscosity than HF with HF?

So we assess the viscosities of the liquids $H F$ and $B {r}_{2}$?
There are dispersion forces between the bromine molecules: the electrons cloud can transiently distort to provide intermolecular interaction. On the other hand, in pure $H F$, the dominant intermolecular force is hydrogen bonding, i.e. ""^(delta+)H-F^(delta-).
But the best indicator of intermolecular force is the boiling point. Bromine has a boiling point of $58.8$ ""^@C; for pure $H F$, $19.5$ ""^@C. On this metric, the intermolecular force is greater for bromine. Given the greater intermolecular attraction, we would anticipate that bromine is more viscous than hydrogen fluoride. This is not an experiment I would care to perform. Both substances are highly corrosive, and can cause horrendous burns.