[demt]

sorry folks, someone had to ask but why is mercury liquid at r.t.p? has it already been asked?

[jdurg]

Okay, to start with let's just go over what makes a metal a metal.  A metal is an element where the nuclei are evenly spaced in a lattice arrangment and the electrons flow around this lattice of positively charged nuceli.  Because the electrons are free to move, metals are able to conduct electricity VERY well.  Metals are also able to conduct heat very well since the energy associated with heat can easily be passed along all of the electrons flowing around these nuclei.

The fact that the nuclei are surrounded in a sea of electrons also means that metals can be beaten and pounded and pulled without breaking as the electrons allow the nuclei to move past each other yet still remain connected.  This strong attraction also means that the positively charged nuclei are fully surrounded by negatively charged electrons, so they have no want/need to go anywhere.  As a result, most metals have a very high melting point and boiling point.  So as you can tell, its the electrons that really play an important role in determining the properties of a metal.

If we look at mercury, we see that it is just to the right of a very noble metal (gold) which is a solid, and to the left of a fairly reactive metal (thallium) which is also a solid.  When looking at the electron configuration of these metals, we see the following:

Au (79):  [Kr]4d10 4f14 5s2 5p6 5d10 6s1
Hg (80):  [Kr]4d10 4f14 5s2 5p6 5d10 6s2
Tl  (81):  [Kr]4d10 4f14 5s2 5p6 5d10 6s2 6p1

Now remember that as we go from gold to thallium, the size of the nucleus increases as does the charge of the nucleus.  Meanwhile, the electron shells don't really increase in size until we get up to Thallium where the 6p subshell starts to fill.  In gold, the 'metal lattice' is made up of nuclei which readily give up that 6s electron and allow it to flow in this sea of electrons.  As a result of this, there is a strong connection between the seemingly positively charged nuclei and the negatively charged electrons.  They want to stick around each other and feel that they need the other atoms to stay together.  Because of this, gold has a pretty high melting point and boiling point, but is a VERY soft metal because the atoms are able to slip past each other yet still remain 'attached'.

With Thallium, the 6s shell is completely filled so the nucleus really won't want to get rid of them as easily.  However, the 6p shell is starting to fill so it can be shared amongst all the other atoms as well.  Thallium has a relatively low melting point, but it's still well above room temperature.  It's a fairly reactive metal as not only will it give up its 6p1 electron to other Tl atoms, but it will also give it up to anything else in the area.  Gold is a bit more conservative with its 6s1 electron.  It will hold onto that tightly since the nucleus of Gold is so huge and has such a strong attraction to any and all electrons.

This brings us to Mercury.  Mercury has a very large nucleus like thallium does, but it also has a completely 'full' 6s subshell unlike gold.  Because of this, one would think that mercury would have a strong attraction to its electrons and not want to share them with other atoms, let alone itself.  This is quite true as mercury is a pretty poor conductor of electricity in terms of a metal, and is not really that great of a conductor of heat either.  So while in a normal metal you have a bunch of positively charged nuclei surrounded by a sea of electrons, in mercury you basically have a bunch of individual atoms which occasionally show a positive charge when an electron jumps around and switches places with other Hg nuclei.  As a result of this, the attraction that each mercury atom has to another Hg atom is VERY poor.  This means that you don't need a lot of energy to move an atom past another.  At room temperature and pressure, there's enough energy to cause Hg to be a liquid.  The mercury nucleus is happy with its own two electrons and really doesn't feel the need to share.  It's a large nucelus, so it will keep those electrons and you get a bunch of negative charges next to each other.  (As the outer shells will be negatively charged and somewhat repel each other, but the very strong charge of the Hg nuclei will still keep a semi 'sea' of electrons).

So why is mercury a liquid?  Because it has a VERY strong attachment to its 6s electrons and doesn't want to give them up, yet the nucleus of mercury is very big and exerts a strong pull on other electrons so the element remains together, but only as a liquid.

[FeLiXe]

never heard that before. sounds good.

to add a  number from my periodic table: Mercury has the highest first ionisation energy of any metal with 10.4 eV