11th Class Chemistry The p-Block Elements-I

  • question_answer 9) Discuss the pattern of variation in the oxidation states of: (i) B to \[Tl\](ii) C to\[Pb\].

    Answer:

    (i) The elements of group 13, exhibit two oxidation states of +3 and +1 in their compounds. Due to small size and high ionisation enthalpies of boron, it forms only covalent compounds showing +3oxidation state. Aluminium shows +3 oxidation state by forming both electrovalent and covalent compounds. However, down the group from \[Ga\]to\[Tl\]due to poor shielding effect of intervening electrons of d- and orbitals, the ns electrons are held firmly and thereby restrict the \[n{{s}^{2}}\] electrons to participate in bonding. As a result of this, only p-orbital electron may be involved in bonding. In fact,\[Ga\], In and\[~Tl\] show both +1 and +3 oxidation states but the relative stability of +1 oxidation state increases and stability of +3 oxidation state decreases due to the inert pair effect. (ii) Carbon and silicon exhibit +4 oxidation due to presence of four electrons in the valence shell and due to not having inert pair effect as d-electrons are not present in penultimate energy shell. In contrast all other elements from \[Ge\]to \[Pb\]exhibit+2 and 44 oxidation states due to the presence of d-and f-electrons. However, the stability of +2oxidation state increases while stability of +4oxidation state decreases due to inert pair effect from \[Ge\]to\[~Pb\], i.e., +2 state of\[~Pb\] is more stable than +4 state of\[~Pb\].


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