Nonmetal

Nonmetal is a general term for a class of chemical elements that lack the typical properties of metals. Most of these elements do not have a metallic lustre, and they conduct heat and electricity poorly. When solid, they are brittle rather than malleable.

Nonmetals are found on the right side of the periodic table, except for hydrogen, which is located in the upper left corner. They include hydrogen, carbon, nitrogen, oxygen, phosphorus, sulphur, selenium, the halogens, and the noble gases.

Physical properties

At room temperature, some nonmetals are gases (such as oxygen and nitrogen), one is liquid (bromine), and the rest are solid (such as carbon and sulphur). Solid nonmetals typically lack metallic lustre and are brittle. Their melting points, boiling points, and densities vary widely and differ from those of metals.

Chemical properties

Nonmetals tend to gain or share electrons when they react. When they combine with metals, they form ionic bonds, whereas when they combine with other nonmetals, they form covalent bonds involving electron sharing. Electronegativity—the ability to attract electrons—is generally high, particularly in fluorine and oxygen.

Classification

Nonmetals are often divided into two or three groups: the noble gases, which are unreactive; the halogens, which are highly reactive; and other nonmetals such as carbon, nitrogen, oxygen, phosphorus, sulphur, and selenium. There also exist elements called metalloids (such as boron, silicon, and germanium) that have mixed properties and whose classification as metals or nonmetals is not sharply defined.

Significance

Nonmetals make up much of the composition of living organisms: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulphur form the basis of life molecules such as proteins and DNA. They are also constituents of air, water, and industrial materials, including fertilizers and medicines.