Why is mercury liquid? [duplicate]

Why is mercury the only metal that is liquid at room temperature?

Note: I am a high school student and would appreciate an answer, if possible, suited for my level of understanding.

Thank you.

marked as duplicate by ron, Klaus-Dieter Warzecha, bon, Loong♦, Martin - マーチン♦May 26 '15 at 0:18

• This question addresses it quite nicely I think. Another great post is by Frank Senese. Especially the referenced publication, J. Chem. Ed., 1991, 68, 110-113 is interesting, but probably behind a paywall pubs.acs.org/doi/abs/10.1021/ed068p110 – Martin - マーチン May 25 '15 at 5:42
• BTW, gallium melts ~30C, "room temperature" in a warm climate (it would melt in your hand, too). – DrMoishe Pippik May 25 '15 at 17:19
• An interesting paper on this was published in 2013. Take a look at this news article with an overview and a link to the paper. – Nicolau Saker Neto May 25 '15 at 21:56

There are a couple of reasons why Mercury is a liquid at STP, I will go through each of them with an explanation that won't be too complex for your understanding.

First of all understanding why most metals are metallic is a good place to start. This happens because of the sharing of valence electrons. The sharing of these electrons make metals malleable and ductile and thus not liquid. Generally the more the electrons shared means the higher the melting point and a harder metal.

OK, getting into the Mercury. Like others have probably mentioned above, Mercury doesn't like to share its electrons. It hangs onto them very tightly and thus Mercury-Mercury bonding is very weak and thus the compound melts and boils at very low temperatures. In other words, Mercury lacks the sea of electrons.

So then, why doesn't it like to share electrons? The $\ce{6s}$ electrons come very close to the nucleus and swing around it at near the speed of light. Due to this, relativistic effects occur. In other words, the $\ce{s}$ electrons behave as if they are more massive than other electrons. This lowers the energy of the electrons. To summarize, the electrons are buried deep in the atomic core and thus aren't able to participate in chemistry.

Overall, since you are a high school student, I would probably just say that Mercury doesn't readily bond well and that is due to the $\ce{6s}$ electrons being very attracted to the atomic core.

• Isn't the sea of electrons what give metals their metallic look? If so, then why is mercury shiny and silvery? – Thomas Eding Oct 20 '16 at 7:40

There is a theory of relativistic effect. According to it, in elements with atomic number 80 or greater, the electrostatic attractive force is very high in the valence shell. This causes the 6s valence electrons of mercury to be actually strongly bonded. Now there is also a theory 'electron sea model' where metals share their valence electrons which leads to adhesive forces among metal atoms. As mentioned earlier mercury's valence shell electrons are strongly attracted to its nucleus so mercury atoms do not benefit from the adhesive forces due to very less sharing of the valence electrons. Hope this answers your question.

At room temp at atmospheric pressure mercury will not readily share valence electrons with other atoms. The mercury atoms won't interact with each other to form a structure or lattice to become a solid.

• This is quite a short answer, and does not really address the why. It might be better suited as a comment or extended to include more information. – Martin - マーチン May 25 '15 at 6:18
• Sorry I've got more info on the topic but it said to keep it simple. What aspect of it should I include more info on if I were to edit the answer? Thank you for feedback :) – Technetium May 25 '15 at 6:48
• I think there should at least be a reason for your first statement, why does mercury not share electrons easily and why is that the reason for not forming a lattice. Right now, it seems you are just stating the obvious. Keeping it simple means here probably only, that the argumentative structure should be easy to follow, with basic explanations. – Martin - マーチン May 25 '15 at 6:55
• And you should not be sorry, I am sure the OP appreciates your help in any case. I just wanted to direct you a little bit, that your answer might not be very satisfactory. In the end we are all working together here. – Martin - マーチン May 25 '15 at 6:57
• I just noticed when I've gone to edit that others have left some answers similar to how I was going to edit mine. Should I remove my answer or just leave it a simplified response. ? Others don't mention the lattice structure ? – Technetium May 26 '15 at 6:51