Period 3 Oxides and Their Reactions

Moving across Period 3, from sodium to argon, provides a controlled way to watch chemical character change as metallic behavior gives way to nonmetallic behavior. One of the most instructive patterns is the acid-base character of the oxides formed by these elements. As you cross the period, the oxides shift from basic, through amphoteric, to acidic, mirroring the shift from metals on the left to nonmetals on the right.

The metals sodium and magnesium form basic oxides. Sodium oxide, $Na_2O$, reacts vigorously with water to form sodium hydroxide, a strong alkali: $Na_2O(s) + H_2O(l) \rightarrow 2NaOH(aq)$. Magnesium oxide, $MgO$, is only slightly soluble but still produces an alkaline solution of magnesium hydroxide. These oxides are basic because the elements are metals; their oxides conta