Final answer:
Exceptions for Zn, Cd, Hg, and Mn in possessing typical metallic structures are due to their unique electron configurations and the inert pair effect, especially in heavier elements of groups 13, 14, and 15, which cause deviations from standard metallic bonding patterns observed in other metals.
Step-by-step explanation:
The textbook statement notes that all metals typically have metallic structures at normal temperatures except for Zn, Cd, Hg, and Mn. This is due to exceptions in their electron configurations and bonding behaviors. For instance, Zn, Cd, and Hg are in group 12 and behave more like alkaline earth metals with a ns² outer electron configuration leading to +2 cations. Particularly, Hg can also form Hg₂²⁺ ion, which has a bond between two Hg atoms. For Mn, it has various oxidation states and complex chemical behavior, which does not lead to a typical metallic structure. The deviation from expected metallic structures is also seen in heavier elements of groups 13, 14, and 15 due to the inert pair effect described in your book, which affects the formation of lower oxidation state cations.
The exception to the typical metallic structures at normal temperatures for the elements Zinc (Zn), Cadmium (Cd), Mercury (Hg), and Manganese (Mn) is due to the inert pair effect and the differences in their electron configurations.
The inert pair effect refers to the relatively low energy of the valence s-electron pair in the heavy elements of groups 13, 14, and 15. This causes a partial loss of valence shell electrons, leading to the formation of unusual ions, such as Tl*, Sn²+, Pb²+, and Bi³+.
Mercury, which is in group 12, also exhibits unexpected behavior by forming a diatomic ion, Hg₂2+, in addition to the expected monatomic ion Hg²+.