# How do compounds differ from their component elements?

The physical and chemical properties of a compound differ from its component elements. For example, the element sodium (Na) is a soft, silvery gray active metal that reacts explosively with water to form sodium hydroxide ($N a O H$) and hydrogen gas (${H}_{2}$). The element chlorine, which exits as a diatomic gaseous molecule ($C {l}_{2}$), has a green color and is toxic. These two elements react to form sodium chloride ($N a C l$), also called common table salt, which is a white crystalline solid that is not toxic and dissolves in water, but does not react with it.