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.
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).
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.
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 pointincreases up to arsenic and then decreases upto bismuth.
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.