A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. 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 of chemistry.
The six commonly recognised metalloids are boron, silicon, germanium, arsenic, 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, but they are brittle and only fair conductors of electricity. Chemically, they behave mostly as nonmetals. They can form alloys with metals. Most of their other physical properties and chemical properties are intermediate in nature. Metalloids are usually too brittle to have any structural uses. They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.
The electrical properties of silicon and germanium enabled the establishment of the semiconductor industry in the 1950s and the development of solid-state electronics from the early 1960s.[1]
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,[2] as the term semimetal has a different meaning in physicsthan in chemistry. In physics, it refers to a specific kind of electronic band structure of a substance. In this context, only arsenic and antimony are semimetals, and commonly recognised as metalloids.
| 13 | 14 | 15 | 16 | 17 | ||
|---|---|---|---|---|---|---|
| 2 | B Boron | C Carbon | N Nitrogen | O Oxygen | F Fluorine | |
| 3 | Al Aluminium | Si Silicon | P Phosphorus | S Sulfur | Cl Chlorine | |
| 4 | Ga Gallium | Ge Germanium | As Arsenic | Se Selenium | Br Bromine | |
| 5 | In Indium | Sn Tin | Sb Antimony | Te Tellurium | I Iodine | |
| 6 | Tl Thallium | Pb Lead | Bi Bismuth | Po Polonium | At Astatine | |
Commonly recognized (86–99%): B, Si, Ge, As, Sb, Te Irregularly recognized (40–49%): Po, At Less commonly recognized (24%): Se Rarely recognized (8–10%): C, Al (All other elements cited in less than 6% of sources) | ||||||
Recognition status, as metalloids, of some elements in the p-block of the periodic table. Percentages are median appearance frequencies in the lists of metalloids.[n 1] The staircase-shaped line is a typical example of the arbitrary metal–nonmetal dividing line found on some periodic tables. | ||||||
https://en.wikipedia.org/wiki/Metalloid
The metallic elements in the periodic table located between the transition metals and the weakly nonmetallic metalloids have received many names in the literature, such as post-transition metals, poor metals, other metals, p-block metals and chemically weak metals; none have been recommended by IUPAC. The most common name, post-transition metals, is generally used in this article. Depending on where the adjacent sets of transition metals and metalloids are judged to begin and end, there are at least five competing proposals for which elements to count as post-transition metals: the three most common contain six, ten and thirteen elements, respectively (see image). All proposals include gallium, indium, tin, thallium, lead, and bismuth.
Physically, these metals are soft (or brittle), have poor mechanical strength, and usually have melting points lower than those of the transition metals. Being close to the metal-nonmetal border, their crystalline structures tend to show covalent or directional bonding effects, having generally greater complexity or fewer nearest neighbours than other metallic elements.
Chemically, they are characterised—to varying degrees—by covalent bonding tendencies, acid-base amphoterism and the formation of anionic species such as aluminates, stannates, and bismuthates (in the case of aluminium, tin, and bismuth, respectively). They can also form Zintl phases (half-metallic compounds formed between highly electropositivemetals and moderately electronegative metals or metalloids).
https://en.wikipedia.org/wiki/Metals_close_to_the_border_between_metals_and_nonmetals
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