Metalloid 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. (In Greek metallon = metal and eidos = sort).
There is no rigorous definition of the term, however the following properties are usually considered characteristic of metalloids:
metalloids often form amphoteric oxides.
metalloids often behave as semiconductors (B,Si,Ge) to semimetals (eg. Sb).
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:
Boron (B)
Silicon (Si)
Germanium (Ge)
Arsenic (As)
Antimony (Sb)
Tellurium (Te)
Polonium (Po)
Astatine (At)
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, however the graphite allotrope displays limited electric conductivity more characteristic of a metalloid. Phosphorus, tin, selenium and bismuth also have allotropes which 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.
In addition, the halogens are found at the right.
The periodic table of the chemical elements is a tabular method of displaying the chemical elements.
Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869.
Mendeleev intended the table to illustrate recurring ('periodic') trends in the properties of the elements.
The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
The periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior.
The table has also found wide application in physics, biology, engineering, and industry. The current standard table contains 117 confirmed elements as of October 16, 2006 (while element 118 has been synthesized, element 117 has not).
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