Predicting the Nature of Bonding in Compounds

Most binary compounds (compounds of two elements) of metals with nonmetals are essentially ionic. All compounds involving only nonmetals are essentially covalent except for compounds containing the NH4+ ion. We do not consider compounds of metals with metals in this course. 

Practically all tertiary compounds (compounds of three elements) contain covalent bonds. If one or more of the elements is a metal, there is likely to be ionic as well as covalent bonding in the compound. 

When some molecules containing only covalent bonds are dissolved in water, the molecules react with the water to produce ions in solution. For example, pure hydrogen chloride, HCl, and pure ammonia, NH3, consist of molecules containing only covalent bonds. When cooled to sufficiently low temperatures (—33°C for NH3, —85°C for HCl), these substances condense to liquids. However, the liquids do not conduct electricity, since they are still covalent and contain no ions. In contrast, when HCl is dissolved in water, the resulting solution conducts electricity well. Aqueous solutions of ammonia also conduct, but poorly. In these cases, the following reactions occur to the indicated extent to yield ions  

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