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Metalloid, or semi metal, is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, nearly every element in the periodic table can be termed either a metal or a nonmetal. However, a few elements with intermediate properties are referred to as metalloids (from the Greek metallon = "metal" and eidos = "sort"). The line that separates metalloids from nonmetals in the periodic table is referred to as the "amphoteric line".

There is no rigorous definition of the term, but the following properties are usually considered characteristic of metalloids:

* metalloids often form amphoteric oxides.
* metalloids often behave as semiconductors (B, Si, Ge).

The concepts of metalloid and semiconductor should not be confused. Metalloid refers to the properties of certain elements in relation to the periodic table. Semiconductor refers to the physical properties of materials (including alloys, compounds) and there is only partial overlap between the two.

The following elements are generally considered metalloids:[1][2]

* Boron (B)
* Silicon (Si)
* Germanium (Ge)[3][4]
* Arsenic (As)[5]
* Antimony (Sb)[5]
* Tellurium (Te)[5][6]
* Polonium (Po)[7][8]

Some allotropes of elements exhibit more pronounced metal, metalloid or non-metal behavior than others. For example, for the element carbon, its diamond allotrope is clearly non-metallic, but the graphite allotrope displays limited electric conductivity more characteristic of a metalloid. Phosphorus, tin, and bismuth also have allotropes that display borderline behavior.

In the standard layout of the periodic table, metalloids occur along the diagonal line through the p block from boron to astatine. Elements to the upper right of this line display increasing nonmetallic behaviour; elements to the lower left display increasing metallic behaviour. This line is called the "stair-step" or "staircase." The poor metals are to the left and down and the nonmetals are to the right and up.

1. ^ E. Sherman and G.J. Weston (1966). Chemistry of the non-metallic elements. Pergamon Press, New York. p. 64.
2. ^ Boylan, P.J. (1962). Elements of Chemistry. Allyn and Bacon, Boston. p. 493.
3. ^ Liu, E (1978). "Fluorination of dimethylmercury, tetramethylsilane and tetramethylgermanium. Synthesis and characterization of polyfluorotetramethylsilanes, polyfluorotetramethylgermanes,bis(trifluoromethyl)mercury and tetrakis(trifluoromethyl)germanium". Journal of Organometallic Chemistry 145: 167. doi:10.1016/S0022-328X(00)91121-5.
4. ^ Schnepf, Andreas (2008). "Metalloid Cluster Compounds of Germanium: Synthesis – Properties – Subsequent Reactions". European Journal of Inorganic Chemistry 2008: 1007. doi:10.1002/ejic.200700969.
5. ^ a b c Casiot, C (2002). "Optimization of the hyphenation between capillary zone electrophoresis and inductively coupled plasma mass spectrometry for the measurement of As-, Sb-, Se- and Te-species, applicable to soil extracts". Spectrochimica Acta Part B Atomic Spectroscopy 57: 173. doi:10.1016/S0584-8547(01)00365-2.
6. ^ Chasteen, Thomas G. (2003). "Biomethylation of Selenium and Tellurium: Microorganisms and Plants". Chemical Reviews 103: 1. doi:10.1021/cr010210+.
7. ^ Polonium-210 Information Sheet
8. ^ Rubin, K (1997). "Degassing of metals and metalloids from erupting seamount and mid-ocean ridge volcanoes: Observations and predictions". Geochimica et Cosmochimica Acta 61: 3525. doi:10.1016/S0016-7037(97)00179-8.

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