Question

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

Answer 1

So we assess the viscosities of the liquids `HF` and `Br_2`?

Explanation:

There are dispersion forces between the bromine molecules: the electrons cloud can transiently distort to provide intermolecular interaction. On the other hand, in pure `HF`, 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 `HF`, `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.