This topic is actually the combination of physics (theory of relativity) and chemistry (Niels Bohr's theory). It is very interesting fact that mercury is the only metal element of periodic table which exists in liquid state at standard temperature and pressure. This presentation covers two factors which actually govern unique chemistry of mercury. 1. Filled nature of orbital 2. Relativistic effect

1. How relativistic mass is
responsible for liquid nature
of mercury?

2. Liquid nature of mercury can be explained based on
following facts:
• Filled nature of orbital
• Relativistic effect

3. Filled nature of the 6s orbital
80Hg : 6s2
, 5d10
Outermost 6s orbital is complete
No need for sharing of electron
Very difficult to remove any electron from completely filled ‘s’
orbital due to its high stability.
↑↓

4. In small clusters the bonding between mercury atoms is
actually because of weak van der Waals forces.
These attractions arise from local charge fluctuations in
neighbouring atoms rather than the sharing of electrons.
As covalent or ionic bond formation is not possible, mercury
atoms having weak interactions exist in liquid form.
+ - + -

5. Filled orbital is not the only criteria for
elements to occur in liquid form
Group 8A elements having complete valence shell exist in gaseous
form.
2He(gas)
1s2
10Ne(gas)
[He] 2s2
, 2p6
18Ar(gas)
[Ne] 3s2
, 3p6
36Kr(gas)
[Ar] 3d10, 4s2
, 4p6

6. But noble gases belong to p block of periodic table, having
chemistry entirely different from mercury of d block.
Mercury is the only elements of d block that is liquid
at room temperature.
30Zn
[Ar] 3d10 4s2
48Cd
[kr] 4d10 5s2
80Hg
[Xe] 4F14 5d10 6s2

7. Liquid state and theory of relativity
Due to special relativity the apparent mass of an object
increases as its velocity approaches the speed of light.
m=
𝒎𝒐
𝟏−
𝒗𝟐
𝒄𝟐
m rest/ invariant mass of body
mo relativistic mass
v velocity of body
c speed of light

8. Niels Bohr's theory of atomic structure
The velocity of an electron is proportional to the atomic number of
an element.
Aa ∝ ve
The electrostatic potential between the nucleus and the electron decreases due
to increase in distance.
PE decrease
PE+KE=constant
KE increase
V increase

9. Relativistic effect
for lighter elements
1H1
The velocity is insignificant For
light elements compared to
the speed of light so relativity
is not considered.
Relativistic effect for
heavier elements
80Hg
80Hg : 6s2
, 5d10
For the 1s electron of mercury
relativistic effect becomes
significant
The electron approaches
about 58% of the speed of
light

10. Mass increase results in a 23% decrease
in the orbital radius
𝐦𝐯𝐫 =
𝐧𝒉
𝟐𝝅
𝐯𝐫 =
𝐧𝒉
𝟐𝝅𝒎
𝐦𝐚𝐬𝐬 ∝
𝟏
𝐨𝐫𝐛𝐢𝐭𝐚𝐥 𝐫𝐚𝐝𝐢𝐮𝐬
Because the radius of an electron orbital is inversely proportional to the
mass of atom

11. Decrease in orbital radius causes stronger attraction between
the nucleus and the electrons.
d and f orbitals are more diffuse than other orbitals so they
insufficiently shielding the s electrons contributing towards
orbital decrease.
Due to relativistic shrinkage it is too difficult for mercury to
share its valence electrons and form strong bonds with other
mercury atoms.

12. Relativistic effect is not significant in case of Zn and Cd due to
smaller atomic number as compared to Hg
30Zn
[Ar] 3d10 4s2
48Cd
[kr] 4d10 5s2
80Hg
[Xe] 4F14 5d10 6s2

13. Quick review
Filled
valence shell
No electron
sharing
No bonding
weak van der
Waals forces
Small
clusters
High atomic
number
Velocity
increases
Orbital radius
decreases
Poor
shielding
No sharing,
no bonding