Energy Spectra in Atoms, Molecules and Solids

ENERGY SPECTRA IN ATOMS, MOLECULES AND SOLIDS

To picture the energy spectra in atoms, molecules and solids let us consider a metal say sodium, which consists of 11 electrons with electronic configuration of 1s² 2s² 2p⁶ 3s¹. The energy spectrum of a single atom is as shown in Fig. 1.14. When two sodium atoms and assembled to form a sodium molecule, the energy spectrum of the molecule is as shown in Fig. 1.15. It is found that for a sodium molecule each atomic levels are splitted into two closely spaced levels.

Similarly if 'N' number of atoms are assembled to form a solid, then we have N number of very closely spaced sub levels so called as energy band as shown in Fig. 1.16.

It can be found that each energy band is separated by the gaps and are known as Energy gap (or) forbidden band gap energy.

It can be seen that the electrons present in the outermost energy band (3s¹) are mixed together and they are free to move over the metals. These free electrons are responsible for the conduction to occur.

Conclusion

Thus we can conclude that the electron moving in a periodic potential lattice will have discontinuous energy values (i.e) they are separated as allowed and forbidden zones (or) bands.