What metals are relatively volatile and why?

Mercury is the only metal that is a liquid at room temperature.

It has weak intermolecular forces and therefore a relatively high vapour pressure (0.25 Pa at 25 °C).

Mercury hangs on to its #6s# valence electrons tightly, so it doesn't share them readily with its neighbours in the metal crystal.

The attractive forces are so weak that mercury melts at -39 °C.

The #6s# electrons are able to get quite close to the nucleus, where they move at speeds close to the speed of light.

The relativistic effects make these electrons behave as if they were much more massive than slower electrons.

The increased mass causes them to spend more time close to the nucleus, so the #6s# orbital contracts, and its electrons are much less available to interact with neighbouring atoms.

Next to mercury, the most volatile metals are the heavier alkali metals.

Whereas mercury has a vapour pressure of 1 Pa at 42 °C, cesium has a vapor pressure of 1 Pa at 144 °C.

The alkali metals have only one #s# electron to share in the metal crystal, so they have weaker interactions than other metals.