chemistry 12th class cbse notes

Atomic and Ionic Radii

  • 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/or f orbitals in heavier members.

Ionization Enthalpy

  • Ionisation 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 ionisation enthalpy of the group 15 elements is much greater than that of group 14 elements in the corresponding periods.
  • The order of successive ionisation enthalpies, as expected is ΔiH1 < ΔiH2 < ΔiH3 (above table).

Electronegativity

  • The electronegativity value, in general, decreases down the group with increasing atomic size.
  • However, amongst the heavier elements, the difference is not that much pronounced.

Metallic Character

  • Group 15 elements are less metallic.
  • Metallic character increases down the group.
  • Nitrogen and phosphorus are non-metals, arsenic and antimony metalloids and bismuth is a metal.

Melting and Boiling Point

  • The boiling points, in general, increase from top to bottom in the group.
  • The melting point increases up to arsenic and then decreases upto bismuth.

Allotropy

  • Except for nitrogen and bismuth, all the elements show allotropy
  • All the elements of this group are polyatomic.
  • Dinitrogen is a diatomic gas while all others are solids.

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