Noble gas electron configurations in ionic compounds

There are some important exceptions to the rules discussed here. For example, tin forms both Sn2+ and Sn4+ ions, and lead forms both Pb2+ and Pb4+ ions. Also, bismuth forms Bi3+ and Bi5+ ions, and thallium forms Tl+ and Tl3+ ions. There are no simple explanations for the behavior of these ions. For now, just note them as exceptions to the very useful rule that ions generally adopt noble gas electron configurations in ionic compounds. Our discussion here refers to representative metals. The transition metals exhibit more complicated behavior, forming a variety of ions that will be considered in Chapter 20. 

TABLE 13.5 Common Ions with Noble Gas Electron Configurations in Ionic Compounds... 

Table 12.3 shows common elements that form ions with noble gas electron configurations in ionic compounds. 

In stable chemical compounds, the atoms tend to achieve a noble gas electron configuration. In the formation of a binary ionic compound involving representative elements, the valence-electron configuration of the nonmetal is completed it achieves the configuration of the next noble gas. The valence or-... 

Because of the contraction and stabilization of the 6s orbital, the outermost, or valence, shell of Au is formed by both the 5d and 6s orbitals. Indeed, electronically, Au is halogen-like, with one electron missing from the pseudo noble gas (closed subshell) configuration. Hence, similar to the existence of halogen X2 molecule, gold also forms the covalent Au2 molecule. In addition, gold also forms ionic compounds such as RbAu and CsAu, in which the Au- anion has the pseudo noble gas electronic configuration. 

When a nonmetal and a representative group metal react to form a binary ionic compound, the ions form so that the valence electron configuration of the nonmetal is completed and the valence orbitals of the metal are emptied. In this way both ions achieve noble gas electron configurations. 

We have already seen that when metals and nonmetals react to form solid binary ionic compounds, electrons are transferred and the resulting ions typically have noble gas electron configurations. An example is the formation of KBr, where the K ion has the [Ar] electron configuration and the Br- ion has the [Kr] electron configuration. In writing Lewis structures, the rule is that... 

FIGURE 1.3 In the ionic compounds NaF and KCl, each atom can achieve a noble gas electronic configuration with a filled octet of electrons. 

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