Question

# Discuss the pattern of variation in the oxidation states of  (i) B to TI (ii) C to Pb.

Solution

## 1)B to Tl- they belong to group $$13$$ elements with electric configuration as $$ns2 np1$$. The atoms of these elements have $$3$$valence electrons, two in s subshell & one in p subshell, therefore all these elements show a maximum of $$+ 3$$ oxidation state. Boron shows only $$+3$$ oxidation state in its compound & other elements also show $$+1$$ oxidation state.The$$+1$$ oxidation state becomes more stable as we move down to the group from boron to thallium. The $$+1$$oxidation state is more stable than $$+3$$ oxidation state because of inert pair effect . In the case of the last element, after the removal of one electron from p orbital, the remaining $$ns2$$ electrons behave like stable noble gases& do not take part in compound formation. This reluctance of the electron pair to take part in the chemical combination is called the inert pair effect. The two electrons present in the s-shell are strongly attracted by the nucleus and do not participate in bonding. This inert pair effect becomes more and more prominent on moving down the group. Hence, $$Ga (+1)$$ is unstable, $$In (+1)$$ is fairly stable, and $$Tl (+1)$$ is very stableGroup 13 elementOxidation stateB $$+3$$Al $$+3$$Ga, In, Tl$$+1, +3$$The stability of the $$+3$$ oxidation state decreases on moving down the group.2) C to $$Pb$$- they belongs to group $$14$$in periodic table & are also called carbon family with electronic configuration of $$ns2 np2$$. Therefore, the most common oxidation state exhibited by them should be +4. However, the $$+2$$ oxidation state becomes more and more common on moving down the group. C and Si mostly show the +4 state. On moving down the group, the higher oxidation state becomes less stable. This is because of the inert pair effect. Thus, although $$Ge, Sn, Pb$$ show both the $$+2$$ and $$+ 4$$ states, the stability of the lower oxidation state increases and that of the higher oxidation state decreases on moving down the group.Group14 elementOxidation state$$C +4$$$$Si +4$$$$Ge, Sn, Pb +2, +4$$Chemistry

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