Ionic compounds classification

In this chapter, you learned about the atom and the three basic subatomic particles protons, neutrons, and electrons. You also learned about the periodic table and about the classification of the various elements on the periodic table. Classifications include metal, metalloid, nonmetal, and classification according to the family (group) and period. You also learned the difference between ions and molecules, and how to name ionic compounds and molecules systematically. 

Figure la. Roozeboom s classification for the distribution of the ionic compounds AX and BX over the solid phase and the aqueous phase. 

Soluble ionic compounds tend to be strong electrolytes, while alcohols and organic compounds are nonelectrolytes. Remember that classification as a strong electrolyte, weak electrolyte, or nonelectrolyte is somewhat subjective. Freshwater can be either a weak electrolyte or a nonelectrolyte depending on its purity. The important consideration in classifying a substance is to what extent an aqueous solution of the substance will conduct electricity. 

The halides of the elements of the second and higher groups of the periodic classification are evidently not ionic compounds in view of the improbability of the formation of poly-charged ions such as 326... 

Solvents may also be classified according to their acid-base properties and in terms of specific solute-solvent interactions. These various classification methods are summarized in Figure 2. The listed classifications facilitate the selection of the appropriate solvent to dissolve a compound, i.e., a solvent of low polarity dissolves covalent compounds of low polarity whereas a highly polar solvent dissolves ionic compounds. 

Above all, we must recognize that any classification of a compound that we might suggest based on electronic properties must be consistent with the physical properties of ionic and covalent substances described at the beginning of the chapter. For instance, HCl has a rather large electronegativity difference (0.9), and its aqueous solutions conduct electricity. But we know that we cannot view it as an ionic compound because it is a gas, and not a solid, at room temperature. Liquid HCl is a nonconductor. 

The binary halides of the elements span a wide range of stoichiometries, stmcture types and properties which defy any but the most grossly oversimplified attempt at a unified classification. Indeed, interest in the halides as a class of compound derives in no small measure from this very diversity and from the fact that, being so numerous, there are many examples of well-developed and well-graded trends between the limiting cases. Thus the fluorides alone include OF2, one of the most volatile molecular compounds known (bp —145°), and Cap2, which is one of the least-volatile ionic compounds (bp 2513°C). Between these extremes of discrete molecules on the one hand, and 3D lattices on the other, is a continuous sequence of oligomers, polymers and extended layer lattices which may be either predominantly covalent [e.g. CIP, (MoPs)4,... 

A substance (such as NaCl) whose aqueous solutions contain ions is called an electrolyte. A substance (such as C12H22O11) that does not form ions in solution is called a nonelectrolyte. The different classifications of NaCl and C12H22O11 arise largely because NaCl is an ionic compound, whereas C12H22O11 is a molecular compound. 

A FIGURE 5.12 Classification of ionic compounds Ionic compounds can be categorized into two types, depending on the metal in the compound. 

The classification of the surfaces by Tasker is based on the formal ionicities (oxidar tion states) of metal atoms. As we already noted, the oxidation state and calculated atomic charges are close only in purely ionic compounds (MgO, for example). As we have seen in Chap. 9, the transition-metal atoms charges differ essentially from the oxidation states due to the covalence part of the chemical bonding with oxygen atom. 

A corresponding anionic mechanism in the presence of a strong base (or electron donor) is plausible. Other cyclic compounds may be susceptible to polymerization by similar ionic mechanisms. Inasmuch as the growth step must be extremely rapid, a chain reaction is indicated and classification with vinyl-type addition polymerizations should be appropriate in such cases. 

Nitrides can be sub-divided into ionic, covalent and interstitial types.An alternate general classification of nitrides, based on bonding classification, as ionic, covalent and metallic has also been applied. Ionic or salt-like nitrides are formed by electropositive elements such as Li, Mg, Ca, Sr, Ba, Cu, Zn, Cd and Hg and possess formulae which correspond to those expected on the basis of the combination of the metal ion with ions. A range of covalent nitrides are known and are exhibited by less electropositive elements such as B, S, P, C and Si. Interstitial nitrides are formed by some transition metals and refer to compounds which can be described in terms of the occupancy of interstitial sites in close packed metallic structures by nitrogen atoms. Oxygen can also be accommodated within these structures and a range of oxynitrides are known to... 

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