• How is HCl molecule formed?
The ‘1s’ orbital of ‘H’ atom containing unpaired electron overlaps the ‘3p’ orbital of chlorine atom containing unpaired electron of opposite spin

7 N has electronic configuration 1s2 2s2 2px 1 2py 1 2pz 1 . Suppose that px orbital of one ‘N’ atom overlaps the ‘px ’ orbital of the other ‘N’ atom giving σ px - px bond along the inter-nuclear axis. The py and pz orbitals of one ‘N’ atom overlap the py and pz orbital of other ‘N’ atom laterally, respectively perpendicular to inter-nuclear axis giving π py -py and π pz -pz bonds. Therefore, N2 molecule has a triple bond between two nitrogen atoms.

O has electronic configuration 1s2 2s2 2px 2 2py 1 2pz 1 . If the ‘py ‘ orbital of one ‘O’ atom overlaps the ‘py ’ orbital of other ‘O’ atom along the inter- nuclear axis, a sigma py - py bond (σpy - py ) is formed. pz orbital of one ‘O’ atom overlaps the pz orbital of other ‘O’ atom laterally, perpendicular to the inter-nuclear axis giving a π pz - pz bond. O2 molecule has a double bond between two oxygen atoms.

Be has electronic configuration 1s2 2s2 . It has no unpaired electrons. It is expected not to form covalent bonds, but it forms two covalent bonds one each with two chlorine atoms. To explain this, an excited state is suggested for Beryllium in which an electron from ‘2s’ shifts to 2px level. Electronic configuration of 4 Be 1s2 2s1 2px 1 and 17Cl 1s2 2s2 2p6 3s2