Re: Why Mercury is Liquid?
- From: Uncle Al <UncleAl0@xxxxxxxxxxxxx>
- Date: Sat, 02 Apr 2005 09:12:23 -0800
Farooq W wrote:
>
> Is there an elementary/intermediate explanation of this phenomenon?
> Yes, sci.chem FAQ (Mar 16 1998-see quited text below) has it, but it is
> described in terms of relativistic quantum mechanics (at least could
> somebody translate it into English!)
Hg is at the end of the d-block. It's valence electrons would be 6s2,
then some 5ds. However, s-orbitals have an antinode at the nucleus.
The heavily charged nucleus brings those s-electrons in very close and
fast resulting in substantial relativistic effects. Bringing all the
s-electrons in closer to the nucleus electrostatically shields the
d-orbitals, which expand - but they are also completely filled and
they don't do low energy interactions. The net effect is that the
valence orbitals are (already) symmetrically filled and then
contracted radially inward. The neutral atom looks like a non-polar
inert boson billard ball.
Gold is 6s1. No matter how you diddle it the neutral atom has an odd
number of highest energy electrons and those result in various bonding
interactions with net spin. Gold chemistry is also extremely
relativistic. Aside from its expected cation chemistry is also
behaves like a halogen, easily forming -1 ions, and exhibits a
remarkable desire to bond with carbon.
AuBe is a weak brittle ionic solid despite having lattice parameters
close to that of pure gold. AuBe is the *only* superconductor in a
chiral crystallographic space group, leading one to wonder whether its
elegantly deduced crystal structure and x-ray powder diffraction
pattern are incorrectly assigned,
1) Structure based on primitive cubic lattice
2) Au and Be atoms displaced along the cubic three-fold axes of the
material
3) No atoms at corners of unit cell!
4) No four-fold symmetry!
5) Au at uuu, (1/2+u)(1/2-u)-u, -u(1/2+u)(1/2-u), (1/2-u)-u(1/2+u);
u = 0.100
6) Be at www, (1/2+w)(1/2-w)-w, -w(1/2+w)(1/2-w), (1/2-w)-w(1/2+w);
w = 0.406
7) Space group P2(1)3
> --------------------------
> "Very few chemistry textbooks discuss relativistic effects on chemical
> properties, despite the availability of a comprehensive review by
> P.Pyykko [12]. There several good introductory articles on the
> derivation and calculation of various relativistic effects in molecules
> and atoms, so I'm not going to include details [13,14,15]. Suffice to
> say, that whilst smaller elements can treated simply, larger elements
> need treatment based on the Dirac equation, which shows that the s
> electrons are approaching
> the speed of light, consequently relativistic effects are important.
> If we take the relativistic mass of mercury (m);-
>
> Mo where
> m = -------------------- c (speed of light) = ~137 atomic
> units
> _____________ v = Z = 80
> / ( v ) 2 Mo = rest mass
> / 1 - ( - )
> \/ ( c )
>
> The masses of the 1s electrons are increased by approximately 20% over
> their rest masses, which means that the radius is decreased by 20% -
> since mass appears in the denominator of Bohr radius calculations. All
> the other s shells also contract, with the 6s contracting ~14%, because
> their electron speeds near the nucleus are comparable, and the
> contraction of the inner part
> of the wave function also pulls in the outer tails. The p orbitals also
> contract a similar amount, and these contractions also results in
> increases the screening for d and f orbitals, which may then expand -
> about 3% for the 5d orbital of mercury.
>
> In mercury, the relativistically-contracted 6s2 orbital is full, thus
> the the two electrons do not contribute much to the metal-metal bond,
> which is not the situation for gold. The bonding in mercury is believed
> to be mainly van der Waals forces with a contribution from 6p orbital
> interaction. The relativistic contraction of the filled 6s2 orbital,
> when added to the
> contraction across the sixth row of the periodic table, results in
> relatively weak Hg-Hg bonds that are responsible for mercury being a
> liquid at room temperature. "
> --------------------
> Thanks.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
- References:
- Why Mercury is Liquid?
- From: Farooq W
- Why Mercury is Liquid?
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