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Binary metal-boron compounds, the metal borides, contain only boron and a metal. They are metallic, very hard, with high melting points. TiB 2, ZrB 2, and HfB 2 have melting points above 3000 °C. [68] Some metal borides find specialized applications as hard materials for cutting tools. [71]
Boron, being a metalloid, is a thermal and electrical insulator at room temperature, but a good conductor of heat and electricity at high temperatures. [8] Unlike boron, the metals in the group are good conductors under normal conditions.
[29] [dubious – discuss] Nonmetals closer to the left or bottom of the periodic table (and so closer to the metals) often have metallic interactions between their molecules, chains, or layers; this occurs in boron, [30] carbon, [31] phosphorus, [32] arsenic, [33] selenium, [34] antimony, [35] tellurium [36] and iodine.
The nonmetals are divided into four classes that complement a four-fold division of the metals, with the noble metals treated as a subset of the transition metals. The metalloids are treated as chemically weak nonmetals, in a manner analogous to their chemically weak frontier metal counterparts.
The chemical elements can be broadly divided into metals, metalloids, and nonmetals according to their shared physical and chemical properties.All elemental metals have a shiny appearance (at least when freshly polished); are good conductors of heat and electricity; form alloys with other metallic elements; and have at least one basic oxide.
Boron forms covalent bonds with other nonmetals and has oxidation states of 1, 2, 3 and 4. [19] [20] [21] Boron does not occur naturally as a free element, but in compounds such as borates. The most common sources of boron are tourmaline, borax, Na 2 B 4 O 5 (OH) 4 ·8H 2 O, and kernite, Na 2 B 4 O 5 (OH) 4 ·2H 2 O. [17] it is difficult to
Lists of metalloids differ since there is no rigorous widely accepted definition of metalloid (or its occasional alias, 'semi-metal'). Individual lists share common ground, with variations occurring at the margins. The elements most often regarded as metalloids are boron, silicon, germanium, arsenic, 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. This is a generic definition that draws on metalloid attributes consistently cited in the literature.