Putting Ions Together Ionic Compounds

When an ionic compound is fonned, the cation and anion attract each other, resulting in a salt (see The Magic of an Ionic Bond Sodium + Chlorine = Table Salt, earlier in this chapter). An important thing to remember is that the compound must be neutral — have equal numbers of positive and negative charges. 

Magnesium, an alkaline earth metal, has two valence electrons that it loses to form a cation with a 2+ charge. The electron configuration for the magnesium cation is 

Bromine, a halogen, has seven valence electrons, so it gains one to complete its octet (eight valence electrons) and form the bromide anion with a 1-charge. The electron configuration for the bromide anion is 

Note that If the anion simply has 1 unit of charge, positive or negative, you normally don t write the 1 you just use the plus or minus symbol, with the 1 being understood. But for the example of the bromide ion, I use the 1. 

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In the same way the common properties of all alkaline solutions are accounted for by the formation of hydroxyl ions, of all solutions of chlorides by the formation of chloride ions, of all sulphates by the formation of sulphate ions, etc. A solution, thus, is a mixture of tAvo or more ionic substances together with the original substance put into the solution, provided the reaction of dissociation has not been complete. It does not follow, hoAvever, that all substances react this Avay Avhen dissolved, or that all compounds of hydrogen form hydrogen ions, of chlorine, chloride ions, etc,... 

Table 3.1, both potassium ions and acetate ions tend to produce soluble compounds. So, KCH3COO will be soluble and hence will dissociate into its constituent ions. Putting all of this together lets us write the total ionic equation ... 

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