Mercury

[potterfan3]

Why is mercury liquid at room temperatue?

[SKA]

because it has a low melting point?

[potterfan3]

....... Fine then let me rephrase the question.... Why does it have a low melting point when metals typically have high melting points.

[SKA]

weaker bonds holding it together means less energy is needed to break them, I would think

[potterfan3]

Yes... I guessed that... but I want to know WHY it has weaker bonds

[SKA]

different charges?
anyway, why do you want to know that?

[potterfan3]

because I'm a nosey git

[jake-the-peg]

Metals are solid because they tend to share their outermost electrons with each other creating a "sea of electrons"

Mercury holds on to its two outermost electrons quite tightly this is to do with the electron shells being contracted

Some notes on it here:
http://antoine.frostburg.edu/chem/senese/101/p eriodic/faq/why-is-mercury-liquid.shtml

[Peter Pedant]

Fantastic answer
OK well fantastic site which gives the answer
Thanks Jake

[I have to say that some of the other answers are well, a bit constipated}

[Teddio]

Mercury atoms have two outer valence electrons which are quite tightly bound to the atom thus preventing the formation of strong interatomic bonds. Although Mercury is in the Transition Block of the Periodic Table, it is not treated as a Transition Metal since its chemistry never involves an unfilled d-orbital.
The elements Thallium, Lead, Bismuth, Tin, Indium and Cadmium, found near Mercury in the Periodic Table, have quite low melting points also, for similar reasons.