Molecular orbitals arising from overlap of 2s atomic orbitals

The valence molecular orbitals in diatomic molecules of second row elements arise from overlap of atomic orbitals on adjacent atoms if the atomic orbitals have similar energy
 
2sσ*  

2sσ
The relative energies of the 2s and 2p atomic orbitals depends on atomic number.  For second row elements like lithium 2s overlaps with 2s to give 2sσ and 2sσ* orbitals.

Compared to 1sσ and 1sσ*, the 2sσ and 2sσ* orbitals
  • have similar shapes
  • extend further from the nucleus
  • are BOTH of higher energy because the 2s atomic orbitals are of higher energy than 1s atomic orbitals.
Dr Sheila Woodgate
© The University of Auckland 2002