Values of the standard enthalpies of atomization,
aHo(298 K), (or sublimation) in Table 5.2 refer to the processes
defined in equation 5.2, and correspond to the destruction
of the metallic lattice. Mercury is an exception, since at
298K it is a liquid.
1
n
Mn(standard state) "MðgÞ ð5:2Þ
Those metals with the lowest values of aHo(298 K) are
again those with other than close-packed structures. Since
aHo appears in thermochemical cycles such as the Born–
Haber cycle (see Section 5.14), it is clear that aHo is
important in accounting for the reactivity patterns of these
metals.
In general, there appears to be a rough correlation
between values of aHo(298 K) and the number of unpaired
electrons. In any long period (K to Ga, Rb to Sn, and Cs to
Bi in Table 5.2), the maximum values are reached in the
middle of the d-block (with the exception of Mn which has
the atypical structure described in Section 5.3).