Chapter 3
B.sc 1st year Book
(Page 2)

# Inert Pair Effect

The oxidation state of metal atoms of groups III A. IV A and V A, all belonging to p – block elements are as follows :
Group III A: Ga (+3, +1); In(+3, +1); IT(+3, +1) (ns2np1)
Group III A: Ge (+4, +2); Sn(+4, +2); Pb(+4, +2) (ns2np1)
Group III A: As (+5, +1); Sb(+5, +3); Bi(+5, +3) (ns2np1)

The lighter elements of these groups boron, carbon, and nitrogen show +3,+4, and +3 oxidation states respectively. But heavier ones show two different oxidation states i.e. variable oxidation states as shown above.

## (i) Higher oxidation state or group oxidation state :

It is represented by the letter ‘G’. The higher oxidation state is equal to the group number of the elements to which they belong. It is also equal to the number of electrons present in their valence shell and called group oxidation state ‘G’. Generally, this number of electrons
take part in chemical bond formation.

## (ii) Lower oxidation state :

The lower oxidation state is equal to the group oxidation state minus two, i.e. G-2. This decrease in oxidation state is due to the fact that np-electrons are involved in the chemical bond formation but ns2 electrons show inertness. The inertness of ns2 electron is called the ‘ inert pair effect.

### Reason for Lower oxidation state:

Let us consider IV-the group elements having electronic configuration ns2, np2 Since the two p-electrons are farther from the nucleus ae compared to ns2electrons, the mine electrons are therefore removed very easily from lower to higher energy levels as compared to ns2 electrons. Hence ns-elections become inert and do not take part in chemical combination Hence Pb2+ is more stable as compared to Pb4+ and shows reluctance to exist in the +4 oxidation state. The inert pair effect increases when we move from Be to Ph Through Sn. The compound of Ge (IV) is more stable as compared to Sn and Pb. Similar His ease with the element it Srd group. TI (1) lo most stable and+1 oxidation state becomes more and more stable as we move dawn tho group lie.
in other words. In the case of the 4th, 5th, and 6th periods of the p-block elements which come after d-block elements, the electrons present in the intervening d- and f- orbitals do not shield the s-electrons of the last shell electron or valence shell effectively. As a result, ns2+ electrons remain more tightly field to the nucleus, and hence do not participate in bonding. This effect is called or known as the “inert pair effect”.

### Group V elements and relative stability of +3 and +5 oxidation states:

The general electronic configuration of these elements is ns2np3. They show +5 and +3 oxidation states. Amongst these +3 oxidation state becomes more and more stable as we move from top to bottom in a group and the +5 oxidation state is very less stable. The reason is the greater stability of a pair of valence shell electrons of ns-orbital. The order of stability of the +3 oxidation state is as follows:

Consequently, bismuth always prefers to form trihaīdes and not pentahalides.
Due to the inert pair effect, the lighter elements of the group IIIA, IVA, and VA prefer to show higher oxidation states and reluctance to show lower oxidation states whereas, on the other hand, heaviest elements like TI, Pb, and Bi prefer to show lower oxidation state. High oxidation state salts of heavier elements of group IIIA, IVA, and VA are unstable and act as strong oxidizing agents. For example, SnCl4 is unstable in solution. It oxidizes to other compounds when reacting with them and reduced itself into dihalide.

Inert Pair effect: The tendency of the two electrons from an outermost subshell atomic s-orbital to remain unshared in compounds/elements for transition metals.

The reluctance of s-orbital electrons(e) to participate in bonding. This is occurred due to the poor shielding and screening effect of the ‘d’ orbital and ‘f’ orbital is known as the Inert Pair effect.

It is one kind of effect proposed by Sidgwick.

Inert pairs involve into account the lower shielding/screening effect of ‘d’ and ‘f’ orbital electrons.

This effect is majorly found in p-block elements of groups 4 and 5 groups.

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Keywords
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