Help with metal boiling points?

Its to do with metallic bonding (see source). When you go down the group the number of protons and electrons in the atoms increase (with atomic number) therefore the difference in charge increases too. This means the attractive force between the metal cation and its electrons (now delocalised remember) is greater so more energy is needed to seperate them - ie boil.

I don't actually know but just to give a point to think about: transition metals are more complicated than other metals in their electron arrangements. As you go down a group, the number of delocalised electrons per atom might increase in transition metals. I guess...

Being a metal (like silver and gold) or a nonmetal (like carbon) doesn't have much to do with phase transitions (such as boiling). silver boils at 2162 °C gold boils at 2856 °C diamond sublimes (solid turns to gas, like dry ice) at 3700-3800 °C (different google hits say different) To make it boil it has to be melted first, which only happens at very high pressures. Diamond melts at the pressures of about 10 million atmosphers (done by Sandia National Laboratories who studied the triple point of carbon: diamond phase/carbon bc8 phase/liquid carbon). I don't think anybody ever boiled liquid carbon.