A Classical Model of Dipole Polarizability

At equilibrium these two forces must be equal and so the displacement d satisfies 

The induced dipole moment is Qd and the polarizability (here a scalar) is Qd/E so that 

Apart from the factor of 4rreo, the polarizability of an atom is determined in this model by the volume. If we had been working in cgs (old-fashioned electromagnetic quantities) rather than SI (modem ones), we would have found a = a and for this reason people speak of the polarizability volume. 

The SI units of polarizability are Fm. Alternatively, since Fm = N we can quote polarizabilities as C N m or C m J , which is the normal form. In the atomic system, it is usual to quote polarizabilities in multiples of e a E.  

The polarizability of the inert gas atoms does indeed increase with their size, as can be seen from Table 17.1. 

---