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Allotropy or allotropism (from Ancient Greek ἄλλος (allos) 'other' and τρόπος (tropos) 'manner, form') is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements.
Elemental boron has been found in star dust and meteorites, but does not exist in the high oxygen environment of Earth. It is difficult to extract from its compounds. The earliest methods involved reduction of boric oxide with metals such as magnesium or aluminium. However, the product is almost always contaminated with metal borides.
Bulk red phosphorus does not ignite in air at temperatures below 240 °C (460 °F), whereas pieces of white phosphorus ignite at about 30 °C (86 °F). Under standard conditions it is more stable than white phosphorus, but less stable than the thermodynamically stable black phosphorus.
Graphite is the most stable allotrope of carbon. Contrary to popular belief, high-purity graphite does not readily burn, even at elevated temperatures. [8] For this reason, it is used in nuclear reactors and for high-temperature crucibles for melting metals. [9]
Atomic oxygen, denoted O or O 1, is very reactive, as the individual atoms of oxygen tend to quickly bond with nearby molecules.Its lowest-energy electronic state is a spin triplet, designated by the term symbol 3 P.
Below 912 °C (1,674 °F), iron has a body-centered cubic (bcc) crystal structure and is known as α-iron or ferrite.It is thermodynamically stable and a fairly soft metal. α-Fe can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form termed ε-Fe discussed below.
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Phase information is based on the work of G. C. Vezzoli, et al., as reviewed by David Young; as Young notes, "The literature on the allotropy of sulfur presents the most complex and confused situation of all the elements." [8] [9] Phase information are limited to ≤50 kbar and thus omitting metallic phases. [10]