Atomic and Physical Properties of Group 15 Elements

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 Δ_iH₁ < Δ_iH₂ < Δ_iH₃ (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.