compound: Properties of Compounds

A compound has unique properties that are distinct from the properties of its elemental constituents. One familiar chemical compound is water, a liquid that is nonflammable and does not support combustion. It is composed of two elements: hydrogen, an extremely flammable gas, and oxygen, a gas that supports combustion. A compound differs from a mixture in that the components of a mixture retain their own properties and may be present in many different proportions. The components of a mixture are not chemically combined; they can be separated by physical means. A mixture of hydrogen and oxygen gases is still a gas and can be separated by physical methods. If the mixture is ignited, however, the two gases undergo a rapid chemical combination to form water. Although the hydrogen and oxygen can occur in any proportion in a mixture of gases, they are always combined in the exact proportion of two atoms of hydrogen to one atom of oxygen when combined in the compound water. Another familiar compound is sodium chloride (common salt). It is composed of the silvery metal sodium and the greenish poisonous gas chlorine combined in the proportion of one atom of sodium to one atom of chlorine.

Sections in this article:

• Introduction
• Molecular and Ionic Compounds
• Properties of Compounds
• Formation and Decomposition of Compounds

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