Zinc group ionization potentials

The melting points, boiling points, and heats of vaporization for the zinc group members are lower than for any other group of metals except la. By the argument presented on page 99, one would expect these metals to have abnormally high" oxidation potentials that is, they should be less noble than other metals with comparable ionization potentials. Thus zinc (ionization potential 9.39 volts) is more easily oxidized than iron (ionization potential 7.90 olts), cadmium (ionization potential 8.9S volts) is more easily oxidized than nickel (ionization potential 7.63 volts), and mercury (ionization potential 10.43 volts) more easily than platinum (ionization potential 8.88 volts). Note that the ionization potentials would favor the opposite order in each case. 

The elements Zn, Cd, and Hg, which have two electrons outside filled penultimate d shells, are also classed in Group II. Although the difference between the calcium and zinc sub-groups is marked, Zn, and to a lesser extent Cd, show some resemblance to Be or Mg in their chemistry. We shall discuss these elements separately (Chapter 18), but it may be noted here that Zn, which has the lowest second ionization potential in the Zn, Cd, Hg group, still has a value (17.89 eV) similar to that of Be (18.21 eV), and its standard potential (—0.76 V) is considerably less negative than that of Mg. 

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