Review of Elements and Compounds

Key Questions

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 ( $N a O H$ $NaOH$ ) and hydrogen gas ( $H_{2}$ $H_2$ ). The element chlorine, which exits as a diatomic gaseous molecule ( $C l_{2}$ $Cl_2$ ), has a green color and is toxic. These two elements react to form sodium chloride ( $N a C l$ $NaCl$ ), 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.

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Figure 23: (a) Sodium metal (immersed in oil to prevent reaction with oxygen and moisture in the air); (b) chlorine gas; (c) the reaction between sodium and chlorine; (d) sodium chloride (common table salt)

Meave60 · 7 · Aug 10 2014
What is an element?

A chemical element is a pure chemical substance consisting of a single type of atom distinguished by its atomic number, which is the number of protons in its atomic nucleus. Elements are divided into metals, metalloids, and non-metals.

Deevona · 3 · Jun 29 2014