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The elements in group 13 are also capable of forming stable compounds with the halogens, usually with the formula MX 3 (where M is a boron-group element and X is a halogen.) [14] Fluorine, the first halogen, is able to form stable compounds with every element that has been tested (except neon and helium), [15] and the boron group is no exception.
Boron atoms lie in hexagonal aromatic graphite-like layers, with a charge of −1 on each boron atom. Magnesium(II) ions lie between layers. 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]
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The Gmelin rare earths handbook lists 1522 °C and 1550 °C as two melting points given in the literature, the most recent reference [Handbook on the chemistry and physics of rare earths, vol.12 (1989)] is given with 1529 °C.
Crystalline boron is a very hard, black material with a high melting point and exists in many polymorphs: Two rhombohedral forms, α-boron and β-boron containing 12 and 106.7 atoms in the rhombohedral unit cell respectively, and 50-atom tetragonal boron are the most common. Boron has a density of 2.34 −3. [17]
It is barely reactive under normal conditions, except for attack by fluorine, [242] and has a melting point of 2076 °C (cf. steel ~1370 °C). [243] Boron is a semiconductor; [244] its room temperature electrical conductivity is 1.5 × 10 −6 S•cm −1 [245] (about 200 times less than that of tap water) [246] and it has a band gap of about 1 ...
This is a list of the various reported boiling points for the elements, with recommended values to be used elsewhere on Wikipedia. ... 5 B boron; use: 4200 K: 3927 ...
The borides can be classified loosely as boron rich or metal rich, for example the compound YB 66 at one extreme through to Nd 2 Fe 14 B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4:1 or more, the compound is boron rich; if it is less, then it is metal rich.