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The p-Block Elements — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe p-Block Elements5 Marks
Question
Discuss the general characteristics of Group $15$ elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativity.
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Answer

  1. Electronic configuration: The valence shell electronic configuration of these elements is $ns^2 np^3.$ The s orbital in these elements is completely filled and p orbitals are half filled, making their electronic configuration extra stable.
  2. Atomic Size: Covalent and ionic (in a particular state) radii increase in size down the group. There is a considerable increase in covalent radius from $N$ to $P$. However, from As to Bi only a small increase in covalent radius is observed. This is due to the presence of completely filled d and f or f orbitals in heavier members.
  3. Oxidation State: The common oxidation states of these elements are $–3, +3$ and $+5.$ The tendency to exhibit $–3$ oxidation state decreases down the group due to increase in size and metallic group. In the last member of the group, bismuth hardly forms any compound in $–3$ oxidation state. The stability of $+5$ oxidation state decreases down the group. The stability of $+5$ oxidation state decreases and that of $+3$ state increases (due to invert pair effect) down the group. Nitrogen exhibits $+1, +2, + 4$ oxidation states also when it reacts with oxygen. Phosphorus also shows $+1$ and $+4$ oxidation states in some oxo acids.
  4. Ionization enthalpy: Ionization enthalpy decreases down the group due to gradual increase in atomic size. Because of the extra stable half filled p orbitals electronic configuration and smaller size, the ionization enthalpy of the group $15$ elements is much greater than that of group 14 elements in the corresponding periods. The order of successive ionization emthalpies are expected as $\triangle H_1, < \triangle H_2 < \triangle H_3.$
  5. Electronegativity: The electronegativity value, in general, decreases down the group with increasing atomic size. However, amongst the heavier elements, the different is not that much pronounced.

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