Question

Why does the melting point of group 15 elements increases as we move down the group from N to As and then decreases at Sb and Bi?

Answer 1

The melting point depend on the no. of unpaired electrons present on atom. Higher the no. of unpaired electron, higher is the melting point. Now the melting point of group 15 elements increases as we move down the group from N to As these elements have tendency to involve all the 5 electron both s and p orbital in bonding but as we move down the group from Sb to Bi, the s orbital electron do not involve in bonding due to inert pair effect which doesn't allow extra two electron to involve in increasing the melting point of an atom.