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Jai Ganesh

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Registered: 2005-06-28

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Nonmetal

Nonmetal

Gist

A nonmetal is a chemical element that lacks the properties of a metal, such as being a poor conductor of heat and electricity and being brittle when solid. Nonmetals can be gases (like oxygen and helium), a liquid (like bromine), or solids (like carbon and sulfur). They tend to have high electronegativity, meaning they attract electrons in chemical reactions.

The 22 nonmetals are hydrogen, helium, carbon, nitrogen, oxygen, fluorine, neon, phosphorus, sulfur, chlorine, argon, selenium, bromine, krypton, iodine, xenon, astatine, radon, tennessine, oganesson, silicon, and boron. Note that silicon and boron are sometimes categorized differently, and the exact classification of the newest elements can vary, but these 22 are commonly listed as nonmetals. 

Summary

A nonmetal, in physics, is a substance having a finite activation energy (band gap) for electron conduction. This means that nonmetals display low (insulators) to moderate (semiconductors) bulk electrical conductivities, which increase with increasing temperature, and are subject to dielectric breakdown at high voltages and temperatures. Like metals, nonmetals may occur in the solid, liquid, or gaseous state. However, unlike metals, nonmetals display a wide range of both mechanical and optical properties, ranging from brittle to plastic and from transparent to opaque.

From a chemical point of view, nonmetals may be divided into two classes: 1) covalent materials, which contain atoms having small sizes, high electronegativities, low valence vacancy to electron ratios, and a pronounced tendency to form negative ions in chemical reactions and negative oxidation states in their compounds; 2) ionic materials, which contain both small and large atoms. Ions may be formed by adding electrons to (small, electronegative atoms) or by extracting electrons from (large, electropositive) atoms. In ionic materials, nonmetals exist either as monatomic anions (e. g., F-in NaF) or as constituents of polyatomic anions (e.g., N and O in the NO3-`s in NaNO3). When in the form of simple elemental substances, about 25 or 22% of the known elements form nonmetals at normal temperatures and pressures, including all of the elements in the S-block of the periodic table and approximately 58% of those in the P-block.

Details

In the context of the periodic table, a nonmetal is a chemical element that mostly lacks distinctive metallic properties. They range from colorless gases like hydrogen to shiny crystals like iodine. Physically, they are usually lighter (less dense) than elements that form metals and are often poor conductors of heat and electricity. Chemically, nonmetals have relatively high electronegativity or usually attract electrons in a chemical bond with another element, and their oxides tend to be acidic.

Seventeen elements are widely recognized as nonmetals. Additionally, some or all of six borderline elements (metalloids) are sometimes counted as nonmetals.

The two lightest nonmetals, hydrogen and helium, together account for about 98% of the mass of the observable universe. Five nonmetallic elements—hydrogen, carbon, nitrogen, oxygen, and silicon—form the bulk of Earth's atmosphere, biosphere, crust and oceans, although metallic elements are believed to be slightly more than half of the overall composition of the Earth.

Chemical compounds and alloys involving multiple elements including nonmetals are widespread. Industrial uses of nonmetals as the dominant component include in electronics, combustion, lubrication and machining.

Most nonmetallic elements were identified in the 18th and 19th centuries. While a distinction between metals and other minerals had existed since antiquity, a classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Since then about twenty properties have been suggested as criteria for distinguishing nonmetals from metals. In contemporary research usage it is common to use a distinction between metal and not-a-metal based upon the electronic structure of the solids; the elements carbon, As and Sb are then semimetals, a subclass of metals. The rest of the nonmetallic elements are insulators, some of which such as silicon and germanium can readily accommodate dopants that change the electrical conductivity leading to semiconducting behavior.

Additional Information

The non-metals are elements on the right of the periodic table. Non-metals can be gases, liquids or solids. Non-metals are dull in colour, not shiny like metals. You can't hammer or shape a non-metal; it will just shatter if you hit it. Sulphur is an example of a non-metal. It's yellow and shatters if you hit it with a hammer. Non-metals don't conduct electricity well: they are insulators. There is one exception: graphite is a non-metal which can conduct electricity.

Oxygen, carbon, sulfur and chlorine are examples of non-metal elements.

Non-metals have properties in common with each other. For example, they are often:

* Poor conductors of heat and electricity
* Dull in their appearance
* Weak and brittle

Some other common properties of non-metals are:

* Generally low melting and boiling points, meaning they are gases and liquids at room temperature
* Not sonorous
* Diamond is a form of carbon. Carbon is a non-metal. In the form of diamond it has a high melting point and is shiny.

Some non-metals do not have all of these common properties.

For example, carbon has two main forms - graphite found in pencils, and diamond. Both graphite and diamond have very high melting points and are shiny.

Graphite conducts electricity, which is not typical of non-metals. However graphite is also brittle which is a typical property of non-metals.

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