Inert Pair Effect | Explanation & Examples

Inert pair effect is shown by those elements whose valance shell is 4 ≤ n, where n is the number of shells. When s-electrons of a heavier atom do not take part in bond formation is called the inert pair effect.

History

In 1927, Nevil Sidgwick was the first person who proposed the term “inert pair”. It has been observed that heavier members of the p-block elements don’t give their s-electrons toward the bond formation and the effect is called the inert pair effect.

History of Inert Pair Effect
Nevil Sidgwick

Now we will discuss the example of group 13, group 14, and group 15.

Group 13Group 14Group 15
BoronCarbonNitrogen
AluminiumSiliconPhosphorus 
GalliumGermaniumArsenic
IndiumTinAntimony
ThalliumLeadBismuth
  • In group 13, Ga, In, and Ti show inert pair effects.
  • In group 14, Ge, Sn, and Pb show the inert pair effect.
  • In group 15, As, Sb and Bi show an inert pair effect.

What is Inert Pair Effect In Group 13?

B5 = [He]2, 2s2, 2p1

Al13 = [Ne]10, 3s2, 3p1

Ga31 = [Ar]18, 3d10, 4s2, 4p1

In49 = [Kr]36, 4d10, 5s2, 5p1

Ti81 = [Xe]54, 4f14, 5d10, 6s2, 6p1

First of all, to know the reason for the inert pair effect, we will know the term shielding effect.

Aluminium, inert pair effect

The valence electron of aluminium is attracted by the nucleus but the valence electron of aluminium show repulsion toward the inert electron of Al. So, the valence electron of the aluminium shows both attraction (towards the nucleus) and repulsion (toward inert electron). The repulsion force of the inert electron of an atom towards the valence electron is called the shielding effect. The order of shielding effect is:

s > p > d > f

Does Gallium Show Inert Pair Effect?

In the case of Gallium, 3d10 is present and 10 electrons in the 3d subshell which is poorly shielded toward 4s2 and 4p1 subshell electrons. It means that 3d10 subshell electrons poorly Shield the 4s2 and 4p1 electrons.

So due to the poor shielding effect, 4s2 subshell electrons are attracted toward the nucleus strongly. That’s why 4s2 not easily loses electrons and does not take part in bond formation and gallium easily loses one electron of 4p1 and forms Ga1+, but if three electrons are removed and form Ga3+, more and more energy is required to form Ga3+. So, the inertness of 4s2 subshell electrons is called the inert pair effect.

Does Indium Show Inert Pair Effect?

In the case of Indium, 4d10 subshell electrons are present and before 4d10, 3d10 is also present. The electrons of 3d and 4d subshell poorly shield toward 5s2 and 5p1 subshell electrons. Due to the poor shielding effect of 3d10 and 4d10 on 5s2 and 5p1, the 5s2 attracted toward the nucleus strongly. That’s why 5s2 does not easily lose electrons and does not take part in bond formation. That’s why indium easily forms In1+ but not In3+. So, the inertness of 5s2 subshell electrons is called the inert pair effect.

Does Thallium Show Inert Pair Effect?

In the case of Thallium, 4f14 and 5d10 subshell electrons are present and as we know the f-subshell has a very poor shielding effect toward the valance electrons. The electrons of 4f and 5d are very poorly shielded by the 6s2 and 6p1 electrons, and 6s2 show a stronger force of attraction toward the nucleus. That’s why thallium 6s2 valance electrons do not take part in bond formation. Thallium easily forms a +1 oxidation state but not +3 and we can say that Ti1+ is more stable than Ti3+. So, the inertness of 6s2 subshell electrons is called the inert pair effect.

As we move from top to bottom in a group, the inert pair effect increase. The order of inert pair effect of group-13 is:

Ti > In > Ga

What is Inert Pair Effect In Group 14?

C6 = [He]2, 2s2, 2p2

Si14 = [Ne]10, 3s2, 3p2

Ge32 = [Ar]18, 3d10, 4s2, 4p2

Sn50 = [Kr]36, 4d10, 5s2, 5p2

Pb82 = [Xe]54, 4f14, 5d10, 6s2, 6p2

Does Germanium Show Inert Pair Effect?

In the case of Germanium, 3d10 subshell electrons are present. The 10 electrons of the d-subshell are poorly shielded from the valance shell electrons of germanium. Due to the poor shielding effect on the valance shell, 4s2 subshell electrons are attracted toward the nucleus strongly and it does not lose electrons easily and does not take part in bond formation. That’s the reason, the germanium loses its 4p2 electrons easily and forms Ge2+ but due to the inertness of 4s2, it does not form Ge4+. We can say that Ge2+ is more stable than Ge4+. So, the inertness of 4s2 subshell electrons is called the inert pair effect.

Does Tin Show Inert Pair Effect?

In the case of Tin, 4d10 subshell electrons are present which is poorly Shield to the valence shell electrons of tin, and the 5s2 subshell electrons are strongly attracted by the nucleus and do not loses their electrons and do not take part in bond formation that’s why tin loses its 5p2 electrons easily and form Sn2+ Oxidation state but not Sn4+ to lose all valance electrons. We can say that Sn2+ is more stable and common than Sn4+. So, the inertness of 5s2 subshell electrons is called the inert pair effect.

Does Lead Show Inert Pair Effect?

In the case of Lead, 4f14 and 5d10 are present which are poorly shielded by the valance electrons of lead. The 6s2 and 6p2 electrons are strongly attracted toward the nucleus and 6s2 does not easily lose electrons and does not take part in bond formation. That’s why lead easily forms a +2 oxidation state rather than +4. We can say that Pb2+ is more stable than pb4+. So, the inertness of 6s2 subshell electrons is called the inert pair effect.

What is Inert Pair Effect In Group 15?

N7 = [He]2, 2s2, 2p3

P15 = [Ne]10, 3s2, 3p3

As33 = [Ar]18, 3d10, 4s2, 4p3

Sb51 = [Kr]36, 4d10, 5s2, 5p3

Bi83 = [Xe]54, 4f14, 5d10, 6s2, 6p3

Group-15 elements like As, Sb, and Bi also show inert pair effect and the order will be:

Bi > Sb > As

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