HARDNESS AND ELECTRIC-DIPOLE POLARIZABILITY - ATOMS AND CLUSTERS

A quantitative relation (eta = 1/2(K/alpha)(1/3)) between electric dip ole polarizability alpha and hardness eta is developed. In this relati on K is a constant and eta and alpha are expressed in au. With K = 0.7 92, using the available alpha data, the above equation is found to rep roduce the experimental eta values for a number of open shell atoms an d monoatomic cations of various charges very satisfactorily. This equa tion applies to the clusters of nonmagic numbers of sodium atoms also. However, for closed shell species, the above equation gives hardness values much tower than the experimental data. This is probably because the equation fails to reveal the ''extra'' amount of stability impart ed to a chemical species by a closed shell configuration. Similar lowe r values of eta are produced by this equation for clusters of magic nu mbers of sodium atoms.