kJ mol – and bond length equal to pm. Since no unpaired electron is present in hydrogen molecule, therefore, it is diamagnetic. . Helium molecule (He ) : The electronic configuration of helium atom is s .
Each helium atom contains electrons, therefore, in He molecule there would be electrons. These electrons will be accommodated in σ s and σ * s molecular orbitals leading to electronic configuration: He : ( σ 1s ) ( σ * 1s ) Bond order of He is ½( – ) = He molecule is therefore unstable and does not exist. Similarly, it can be shown that Be molecule ( σ s ) ( σ * s ) ( σ s ) ( σ * s ) also does not exist. .
Lithium molecule (Li ) : The electronic configuration of lithium is s , s . There are six electrons in Li . The electronic configuration of Li molecule, therefore, is Li : ( σ s ) ( σ * s ) ( σ s ) The above configuration is also written as KK( σ 2s) where KK represents the closed K shell structure ( σ s ) ( σ * s ) . From the electronic configuration of Li molecule it is clear that there are four electrons present in bonding molecular orbitals and two electrons present in antibonding molecular orbitals.
Its bond order, therefore, is ½ ( – ) = . It means that Li molecule is stable and since it has no unpaired electrons it should be diamagnetic. Indeed diamagnetic Li molecules are known to exist in the vapour phase. .
Carbon molecule (C ): The electronic configuration of carbon is 1s 2s 2p . There are twelve electrons in C . The electronic configuration of C molecule, therefore, is C