In Chapter 4 we saw examples of equal sharing of electrons in a bond (methane), unequal sharing (ammonia, water, HF), and partial or complete transfer of electrons to form ions (HF and LiF in water).

Ions and salts were introduced primarily as a contrast to electron-sharing. Now we turn to the behavior of ions as they are encountered in salts, solutions, and metals.

Acids and bases were introduced in Chapter 4 with examples of each: the acid HF and the bases and LiOH. Some of the most common and useful acids and bases are oxygen compounds.

In this chapter we shall look at oxygen compounds of the second-shell elements and see why electronegativity differences make some of them acids and others bases. Why, for example, does lithium hydroxide (LiOH) behave so differently from nitric acid ?

Finally, although the brittle salts and flexible metals both are made from ions, they are as different in properties as two solids can be.