Why is mercury a liquid?

Most book say that mercury is a liquid due to the "inert pair" effect. This is a cop out!

The reason is to do with 'reletivistic contraction'.

Can a physist explain this so a simple chemist can underdstand it!!

Originally posted by najdorfslayer
Most book say that mercury is a liquid due to the "inert pair" effect. This is a cop out!

The reason is to do with 'reletivistic contraction'.

Can a physist explain this so a simple chemist can underdstand it!!

I had absolutely no idea why myself so I googled it and got this:

http://antoine.frostburg.edu/chem/senese/101/periodic/faq/why-is-mercury-liquid.shtml

….
….Mercury hangs on to its valence 6s electrons very tightly. Mercury-mercury bonding is very weak because its valence electrons are not shared readily. ….
…
…
Why is the pair of 6s electrons so inert? The s electrons are able to come very close to the nucleus. They swing around very massive nuclei at speeds comparable to that of light. When objects move at such high speeds, relativistic effects occur. The s electrons behave as though they were more massive than electrons moving at slower speeds. The increased mass causes them to spend more time close to the nucleus. This relativistic contraction of the 6s orbital lowers its energy and makes its electrons much less likely to participate in chemistry- they're buried deep in the atomic core.
..…

The link also gives more relevant info on this.
I never realised that relativity can explain the physical properties of an element so explicitly! -this at least appears to be yet another peace of strong evidence to vindicate relativity.

I also found this link:

http://www.madsci.org/posts/archives/1997-05/862179191.Ch.r.html

I hope this helps.

Originally posted by Andrew Hamilton
I had absolutely no idea why myself so I googled it and got this:

http://antoine.frostburg.edu/chem/senese/101/periodic/faq/why-is-mercury-liquid.shtml

….
….Mercury hangs on to its valence 6s electrons very tightly. Mercury-mercury bonding is very weak because its valence electrons are not shared readily. ….
…
…
Why is the pair of 6s electr link:

http://www.madsci.org/posts/archives/1997-05/862179191.Ch.r.html

I hope this helps.

Cheers 🙂

But it doesn't really explain it well enough for me 🙁
The problem is my knowledge of quantum physics and physcs in gereral is good but maybe not good enough to really grasp this to understand it fully! 🙁

Calculations on atoms are extremely complicated, and only the hydrogen atom can be calculated analytically using quantum physics.

If mercury hangs on to its valence electrons, why can it be a conductor of electricity? I thought you had to have loose electrons to be able to bump them around in a conductor.
One of the links explained that one. So does anyone know of other atoms with relativistic contraction of its inner valence electrons? What atom has the fasted electron, the most relativistic?

I think most big atoms have an inert 6s2 pair of electrons.

This is why lead's main oxidation number s +2 not +4 as it is with carbon and silicon etc.

Originally posted by najdorfslayer
I think most big atoms have an inert 6s2 pair of electrons.

This is why lead's main oxidation number s +2 not +4 as it is with carbon and silicon etc.

By that you mean relativistic electrons? I know about the mass V velocity equation, and it says there is not much going on in the way of mass increase or time shifts till you get to around 0.9C, and even at that velocity, the increase in mass is maybe 2X. Is there any way to actually tell the velocity of those relativistic electrons?

Originally posted by najdorfslayer
Most book say that mercury is a liquid due to the "inert pair" effect. This is a cop out!

The reason is to do with 'reletivistic contraction'.

Can a physist explain this so a simple chemist can underdstand it!!

Because its melting point is below room temperature.

Originally posted by sonhouse
By that you mean relativistic electrons? I know about the mass V velocity equation, and it says there is not much going on in the way of mass increase or time shifts till you get to around 0.9C, and even at that velocity, the increase in mass is maybe 2X. Is there any way to actually tell the velocity of those relativistic electrons?

If I'm not mistaken the electron velocity can be deduced from the ionization energy of that particular electron, though I'm not sure if one can free an electron which is not the most weakly bound.

Originally posted by sasquatch672
Because its melting point is below room temperature.

But why?

Originally posted by najdorfslayer
But why?

You can solve the Dirac equation for hydrogen. The Dirac equation is the equation for the wave-function of a relativistic electron. It predicts slightly lower energy levels than the Schrödinger equation (i.e. more tightly bound),

To first order the energy levels go as:

E_n = -13.6/n² (1 + a²/n²(2n - 3/4))

for the s-orbitals of hydrogen. a is the fine structure constant and is ~1/137. This is a tiny effect, I really don´t believe it explains mercury being a liquid at STP. The presence of 81 other electrons is going to be more important.

Originally posted by DeepThought
You can solve the Dirac equation for hydrogen. The Dirac equation is the equation for the wave-function of a relativistic electron. It predicts slightly lower energy levels than the Schrödinger equation (i.e. more tightly bound),

To first order the energy levels go as:

E_n = -13.6/n² (1 + a²/n²(2n - 3/4))

for the s-orbitals of hydrogen. a is t ...[text shortened]... ercury being a liquid at STP. The presence of 81 other electrons is going to be more important.

Mmmm this seems to be the problem I am a chemist (an Organic Chemist at that!) and my quantum mechanics is okay but once the high level maths kicks in I 'm afraid it goes a bit beyond me!

Originally posted by KazetNagorra
If I'm not mistaken the electron velocity can be deduced from the ionization energy of that particular electron, though I'm not sure if one can free an electron which is not the most weakly bound.

I just wondered if you could put a number on how much more mass such a relativistic electron has than a 'rest mass' electron in a given atom like mercury. If you knew that, it would be just arithmetic to find the velocity.

Originally posted by sonhouse
I just wondered if you could put a number on how much more mass such a relativistic electron has than a 'rest mass' electron in a given atom like mercury. If you knew that, it would be just arithmetic to find the velocity.

The electrons are in symmetric orbitals. If you work out the expectation value for their momentum you get zero. The Lamb shift for the 6s state in is of the order of one part in 30,000. Using E = mc² the change in mass of the electron (*) is of the same order of magnitude. I really do not believe that mercury being a liquid at STP is due to an effect that small.

(*) mass is relativity is a tricky concept. The rest mass of the electron does not change. The observed mass of the whole atom does, but it is a composite and its mass is the masses of the constituents less the binding energy.

After a bit of extra thought, the point is that the 6s orbital is very stable. This is a property of the symmetry of the orbital. Hydrogen bonds readily, this is because there is only one electron in the 1s orbital, and it can form a molecule with another hydrogen and get an energy advantage from doing so. Mercury is odd, because it´s most loosely bound electrons are in complete orbits in an s-orbital - generally the s-orbit will be full with p-orbits remaining unfilled. In helium (1s orbital filled with 2 electrons) this means complete non-reactivity. The point is that you can get 2 electrons in the orbital whose spins are oppositely aligned and so magnetic dipole effects cancel. Since in mercury the relevant orbit is the 6s orbit, which is full with two electrons, the reason it is stable in because the electrons spins are aligned. The reason mercury is remotely reactive is due to the last orbits being shielded by 5 layers of other electrons.

The explanation of spin comes from the Dirac equation, and is a relativistic effect in itself. However, I think that the explanation for mercury being a liquid at STP - when almost all others are not - is not to do with the Lamb shift, but simply the rarity of an element whose valence electrons are in a s-orbital. I think the true explanation is in terms of symmetry and not relativity.