Formation of Binary Ionic Compounds

The structures of ionic solids will be discussed in detail in Chapter 16. 

We can illustrate the energy changes involved in the formation of an ionic solid by considering the formation of solid lithium fluoride from its elements  

To see the energy terms associated with this process, we take advantage of the fact that energy is a state function and break this reaction into steps, the sum of which gives the overall reaction. 

Sublimation of solid lithium. Sublimation involves taking a substance from the solid state to the gaseous state  

Ionization of lithium atoms to form Li ions in the gas phase  

For isoelectronic ions, size generally decreases as 1 increases. 

8 to 13 as we go from the 02 ion to the Al3+ ion. Thus, in going from O2-to Al, +, the 10 electrons experience a greater attraction as the positive charge on the nucleus increases. This causes the ions to become smaller. You can confirm this by looking at Fig. 13.7. In general, for a series of isoelectronic ions, the size decreases as the nuclear charge (Z) increases. 

Arrange the ions Se2, Br , Rb +, and Sr2+ in order of decreasing size. Solution 

This is an isoelectronic series of ions with the krypton electron configuration. Since these ions all have the same number of electrons, their sizes will depend on nuclear charge. The Z values are 34 for Se2, 35 for Br, 37 for Rb+, and 38 for Sr2+. Since the nuclear charge is greatest for Sr2+, it is the smallest of these ions. The Se2 ion is largest  

The lattice energy is often defined as the energy released when an ionic solid forms from its ions. However, in this book the sign of an energy term is 

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Oxidation, Reduction, and the Formation of Binary Ionic Compounds... 

Depict the formation of binary ionic compounds with electron configurations, partial orbital diagrams, and Lewis electron-dot symbols ( 9.2) (SP 9.1) (EPs 9.16-9.19)... 

Ionic compounds consist of positive ions (cations) and negative ions (anions) hence, ionic compounds often consist of a metal and nonmetal. The electrostatic attraction between a cation and anion results in an ionic bond that results in compound formation. Binary ionic compounds form from two elements. Sodium chloride (NaCl) and sodium fluoride (NaF) are examples of binary ionic compounds. Three elements can form ternary ionic compounds. Ternary compounds result when polyatomic ions such as carbonate (C032 ), hydroxide (OH-), ammonium (NH4+), form compounds. For example, a calcium ion, Ca2+, combines with the carbonate ion to form the ternary ionic compound calcium carbonate, CaC03. Molecular compounds form discrete molecular units and often consist of a combination of two nonmetals. Compounds such as water (H20), carbon dioxide (C02), and nitric oxide (NO) represent simple binary molecular compounds. Ternary molecular compounds contain three elements. Glucose ( 12 ) is a ternary molecular compound. There are several distinct differences between ionic and molecular compounds, as summarized in Table 1.2. 

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... 

As we saw in Chapter 3, this transfer of electrons from metal atoms to nonmetal atoms is the general process for the formation of any binary ionic compound from its elements. For example, when sodium chloride is formed from the reaction of metallic sodium with gaseous chlorine, each sodium atom loses an electron, and each chlorine atom gains one. 

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-... 

Use the octet rule to correctly predict the ions formed during the formation of ionic compounds, and write correct formulas for binary ionic compounds containing a representative metal and a representative nonmetal. (Section 4.3)... 

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