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Jai Ganesh

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Registered: 2005-06-28

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Metalloid

Metalloid

Gist

A metalloid is a chemical element that has properties intermediate between those of metals and nonmetals, and is also known as a semimetal. These elements are often semiconductors and have a metallic luster but are brittle. Common metalloids include boron, silicon, germanium, antimony, and tellurium.

A metalloid is an element that possesses a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals, and which is therefore hard to classify as either a metal or a nonmetal.

Metalloids are solids that have both metallic and nonmetallic characteristics, such as a shiny, brittle appearance and intermediate electrical conductivity. They are semiconductors, meaning their conductivity falls between that of a metal and a nonmetal. Chemically, they often behave as nonmetals, have intermediate electronegativity and ionization energy, and can form alloys with metals. 

Summary

The word metalloid comes from the Latin metallum ("metal") and the Greek oeidḗs ("resembling in form or appearance"). However, there is no standard definition of a metalloid and no complete agreement on which elements are metalloids. Despite the lack of specificity, the term remains in use in the literature.

The six commonly recognised metalloids are boron, silicon, germanium, As, antimony and tellurium. Five elements are less frequently so classified: carbon, aluminium, selenium, polonium and astatine. On a standard periodic table, all eleven elements are in a diagonal region of the p-block extending from boron at the upper left to astatine at lower right. Some periodic tables include a dividing line between metals and nonmetals, and the metalloids may be found close to this line.

Typical metalloids have a metallic appearance, may be brittle and are only fair conductors of electricity. They can form alloys with metals, and many of their other physical properties and chemical properties are intermediate between those of metallic and nonmetallic elements. They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.

The term metalloid originally referred to nonmetals. Its more recent meaning, as a category of elements with intermediate or hybrid properties, became widespread in 1940–1960. Metalloids are sometimes called semimetals, a practice that has been discouraged, as the term semimetal has a more common usage as a specific kind of electronic band structure of a substance. In this context, only As and Sb are semimetals, and commonly recognised as metalloids. 

Details

A metalloid is a chemical element with properties that fall between those of metals and nonmetals. The term typically refers to a group of between six and eight elements—boron, silicon, Ge, As, Sb, tellurium, and possibly, polonium and astatine—found near the center of the P-block or main block of the periodic table. These elements are classified as metalloids because they share certain physical characteristics with metals, such as luster or moderate conductivity, while they exhibit chemical behavior similar to nonmetals—often forming covalent bonds and acidic oxides.

Properties:

Physical properties

* Appearance: They exhibit a metallic luster, giving them a shiny appearance. However, like nonmetals, they are brittle and can shatter under stress.
* Electrical conductivity: They generally act as semiconductors, meaning that they can conduct electricity under certain conditions—this property makes them essential in electronic and photovoltaic devices.
* Thermal conductivity: Their ability to conduct heat falls between that of metals and nonmetals; they are better thermal conductors than nonmetals but not as efficient as metals.
* Density and melting and boiling points: Metalloids usually have densities and melting and boiling points that are intermediate between those of metals and nonmetals, contributing to their classification as a distinct group.
* Allotropy: Metalloids exist in allotropes (multiple structural forms), such as silicon, which appears as amorphous silicon, a brown powder, and crystalline silicon, which has a metallic luster and gray color.

Chemical properties

* Oxidation states: Each metalloid can exhibit more than one oxidation state, which allows these elements to form a wide range of chemical compounds.
* Electronegativity: Metalloids have electronegativity values that fall between those of metals and nonmetals. Metals are generally less electronegative and tend to form ionic compounds, whereas nonmetals are more electronegative and tend to form covalent bonds. Because metalloids sit in the intermediate range, they can form either ionic or covalent bonds, depending on the element with which they react.
* Acid-base behavior: Metals generally react with acids and nonmetals with bases. Metalloids are often amphoteric, meaning that they can react with both acids and bases.

Uses

Metalloids are used in several industries. In electronics silicon and germanium are used as semiconductors in devices such as computer chips, solar cells, and transistors. In glass and ceramics, boron and silicon improve strength and resistance to thermal shock. Borosilicate glass, which includes boron, is used in laboratory equipment and cookware.

Metalloids contribute to alloy production. Silicon is added to aluminum for better casting properties, while boron strengthens steel. Sb and As are used in lead alloys for batteries, bullets, and solders. Antimony compounds also serve as flame retardants.

Additional Information

Some elements are “none of the above.” They don’t fit neatly into the categories of metal or non-metal because of their characteristics. A metalloid is an element that has properties that are intermediate between those of metals and nonmetals. Metalloids can also be called semimetals. On the periodic table, the elements colored yellow, which generally border the stair-step line, are considered to be metalloids. Notice that aluminum borders the line, but it is considered to be a metal since all of its properties are like those of metals.

Examples of Metalloids

Silicon is a typical metalloid. It has luster like a metal, but is brittle like a nonmetal. Silicon is used extensively in computer chips and other electronics because its electrical conductivity is in between that of a metal and a nonmetal.

Boron is a versatile element that can be incorporated into a number of compounds. Borosilicate glass is extremely resistance to thermal shock. Extreme changes in the temperature of objects containing borosilicates will not create any damage to the material, unlike other glass compositions, which would crack or shatter. Because of their strength, boron filaments are used as light, high-strength materials for airplanes, golf clubs, and fishing rods. Sodium tetraborate is widely used in fiberglass as insulation and also is employed in many detergents and cleaners.

Antimony is a brittle, bluish-white metallic material that is a poor conductor of electricity. Used with lead, antimony increases the hardness and strength of the mixture. This material plays an important role in the fabrication of electronic and semiconductor devices. About half of the antimony used industrially is employed in the production of batteries, bullets, and alloys.

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