Only metal liquid at room temp?

(Image of pound coin floating in mercury.  Source 2)

The only metal that is liquid at room temperature is mercury, a.k.a. quicksilver, Hg, or hydragyrum (meaning "liquid silver" in Latin) (Source 1).

But...why?

"The reason mercury manages to be a liquid at room temperature is 

because its bonding structure is weaker 

than that of most metals. The electrons that spin around mercury nuclei don't easily maintain linkages with other mercury atoms at standard temperatures, hence the lack of solidity [source: Senese]. Mercury is also something of an oddity for another reason, considering where it sits on the periodic table: The elements around it are much better at conducting heat and electricity.

Its liquid form makes mercury is a very versatile element, however. It conducts electricity and is used in switches, and it's also in barometers and thermometers. It can also be combined with a variety of other metals. Mercury on its own is poisonous, and when combined with other elements, it can form different compounds, which are used in everything from antiseptics and pesticides to batteries, fluorescent lamps and detonators for explosives [source: Jefferson Lab]."    (Source 1)

When mercury contacts aluminum, it disintegrates it.  (Source 3)

Because of this, mercury, like in thermometers, is not allowed on airplanes:

"Due to the reactivity of aluminium amalgam, restrictions are placed on the use and handling of mercury in proximity with aluminium. In particular, large amounts of mercury are not allowed aboard aircraft under most circumstances because of the risk of it forming amalgam with exposed aluminium parts in the aircraft.^[4] In the Second World War, mercury may have been used to sabotage aircraft.^[5] Accidental mercury spills in aircraft do sometimes result in insurance write-offs.^[6]"  (Source 4)


Bibliography


1. "Why is mercury considered a metal but it's liquid at room temperature?" Discovery Channel Answer, 2011.  WWW: http://curiosity.discovery.com/question/mercury-metal-and-liquid.


2. "Mercury" blog post by antonii.  Glogster, 2012.  WWW: http://www.glogster.com/antonii/mercury/g-6mmkkqv0cnvq4oc68g6iua0?old_view=True.


3. "Mercury attacks Aluminum" YouTube video by periodictabledotcom.  Uploaded 2009.  WWW: http://www.youtube.com/watch?feature=fvwrel&v=Z7Ilxsu-JlY&NR=1.


4. "Aluminum amalgam" article by Wikipedia, 2012.  WWW: http://en.wikipedia.org/wiki/Aluminium_amalgam.