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Beryllium (Be) is the chemical element with the symbol Be and atomic number 4.

A bivalent element, beryllium is found naturally only combined with other elements in minerals. Notable gemstones which contain beryllium include Beryl (aquamarines and emeralds) and Chrysoberyl (Alexandrite and Cat's eye). The free element is a steel-grey, strong, lightweight brittle alkaline earth metal. It is primarily used as a hardening agent in alloys, notably beryllium copper. Structurally, beryllium's very low density (1.85 times that of water), high melting point (1278 °C), high temperature stability, and low coefficient of expansion with temperature, make it in many ways an ideal aerospace material, and it has been used in rocket nozzles and is a significant component of planned space telescopes. Because of its relatively high transparency to X-rays and other ionizing radiation types, beryllium also has a number of uses as filters and windows for radiation and particle physics experiments.

Commercial use of beryllium metal presents technical challenges due to the toxicity (especially by inhalation) of beryllium-containing dusts. Beryllium produces a direct corrosive effect to tissue, and is also capable of producing a chronic life-threatening allergic disease called berylliosis in susceptible persons.

Beryllium is a relatively rare element in both the Earth and the universe, because it is not formed in conventional stellar nucleosynthesis, but rather during the Big Bang, and later from the action of cosmic rays on interstellar dust. The element is not known to be necessary or useful for either plant or animal life.

Beryllium was discovered by Louis-Nicolas Vauquelin in 1798 as a new element in beryl and in emeralds. Friedrich Wöhler and Antoine Bussy independently isolated the metal in 1828 by reacting potassium and beryllium chloride. Beryllium's chemical similarity to aluminum was probably why beryllium was missed in previous searches.

Etymology
The name beryllium comes from the Greek βήρυλλος, bērullos, beryl, from Prakrit veruliya, from Pāli veuriya; ] veiru or, viar, "to become pale," in reference to the pale semiprecious gemstone beryl. For about 160 years, beryllium was also known as glucinium (with the accompanying chemical symbol "Gl"), the name coming from the Greek word for sweet, due to the sweet taste of its salts.

Characteristics

Physical
Beryllium has one of the highest melting points of the light metals. It has exceptional elastic rigidity (Young’s modulus 316 GPa). The modulus of elasticity of beryllium is approximately 50% greater than that of steel. The combination of this modulus plus beryllium's relatively low density gives it an unusually fast sound conduction speed at standard conditions (about 12.9 km/s). Other significant properties are the high values for specific heat (1925 J/kg·K) and thermal conductivity (216 W/m·K), which make beryllium the metal with the best heat dissipation characteristics per unit weight. In combination with the relatively low coefficient of linear thermal expansion (11.4 × 10-6 K-1), these characteristics ensure that beryllium demonstrates a unique degree of dimensional stability under conditions of thermal loading.

At standard temperature and pressures beryllium resists oxidation when exposed to air (its ability to scratch glass is due to the formation of a thin layer of the hard oxide BeO). It resists attack by concentrated nitric acid.

Nuclear
Beryllium has a large scattering cross section for high energy neutrons, thus effectively slowing the neutrons to the thermal energy range where the cross section is low (0.008 barn). The predominant beryllium isotope 9Be also undergoes a (n,2n) neutron reaction to 8Be, i.e. beryllium is a neutron multiplier releasing more neutrons than it absorbs. Beryllium is highly permeable to X-rays, and neutrons are liberated when it is hit by alpha particles.

Isotopes
Main articles: Isotopes of beryllium and beryllium-10
Plot showing variations in solar activity, including variation in 10Be concentration. Note that the beryllium scale is inverted, so increases on this scale indictate lower beryllium-10 levelsOf beryllium's isotopes, only 9Be is stable and the others are relatively unstable or rare. It is thus a mononuclidic element.

Cosmogenic 10Be is produced in the atmosphere by cosmic ray spallation of oxygen and nitrogen. Cosmogenic 10Be accumulates at the soil surface, where its relatively long half-life (1.51 million years) permits a long residence time before decaying to 10B. Thus, 10Be and its daughter products have been used to examine soil erosion, soil formation from regolith, the development of lateritic soils, as well as variations in solar activity and the age of ice cores. Solar activity is inversely correlated with Be-10 production, because solar-wind decreases flux of galactic cosmic rays which reach Earth.

Beryllium-10 is also formed in nuclear explosions by a reaction of fast neutrons with 13C in the carbon dioxide in air, and is one of the historical indicators of past activity at nuclear test sites.[citation needed]

The fact that 7Be and 8Be are unstable has profound cosmological consequences as it means that elements heavier than beryllium could not be produced by nuclear fusion in the Big Bang, since there was insufficient time during the nucleosynthesis phase of the Big Bang expansion to produce carbon by fusion of 4He nuclei and the relatively low concentrations of 8Be available because of its short half-life. Astronomer Fred Hoyle first showed that the energy levels of 8Be and 12C allow carbon production by the triple-alpha process in helium-fueled stars where more synthetic time is available, thus making life possible from the supernova "ash" from these stars. (See also Big Bang nucleosynthesis).

7Be decays by electron capture, therefore its decay rate is dependent upon its electron configuration - a rare occurrence in nuclear decay.

The shortest-lived known isotope of beryllium is 13Be which decays through neutron emission. It has a half-life of 2.7 × 10-21 second. 6Be is also very short-lived with a half-life of 5.0 × 10-21 second.[citation needed]

The exotic isotopes 11Be and 14Be are known to exhibit a nuclear halo.

Chemical
Beryllium has the electronic configuration [He]2s2. In its chemistry Beryllium exhibits the +2 oxidation state and the only evidence of lower valent Benm+ is in the solubility of the metal in BeCl2.[12] The small atomic radius ensures that the Be2+ ion would be highly polarizing leading to significant covalent character in beryllium's bonding. Beryllium is 4 coordinate in complexes e.g. [Be(H2O)4]2+ and tetrahaloberyllates, BeX42-. This characteristic is used in analytical techniques using EDTA as a ligand which preferentially forms octahedral complexes - thus absorbing other cations such as Al3+ which might interfere, for example in the solvent extraction of a complex formed between Be2+ and acetylacetone.

Beryllium metal sits above aluminium in the electrochemical series and would be expected to be a reactive metal, however it is passivated by an oxide layer and does not react with air or water even at red heat. Once ignited however beryllium burns brilliantly forming a mixture of beryllium oxide and beryllium nitride. Beryllium dissolves readily in non-oxidising acids,(HCl, H2SO4) but not in nitric as this forms the oxide and this behaviour is similar to that of aluminium metal. Beryllium, again similarly to aluminium, dissolves in warm alkali to form the beryllate anion, Be(OH)42- , and hydrogen gas. The solutions of salts, e.g beryllium sulfate and beryllium nitrate are acidic because of hydrolysis of the [Be(H2O)4]2+ ion: eg [Be(H2O)4]2+ + H2O <> [Be(H2O)3(OH)]+ + H3O+

Compounds
See also: Category:Beryllium compounds
Beryllium forms binary compounds with many non-metals. Beryllium hydride is an amorphous white solid believed to be built from corner-sharing {BeH4} tetrahedra.

All four anhydrous halides are known. BeF2 has a silica-like structure with corner-shared {BeF4} tetrahedra. BeCl2 and BeBr2 have chain structures with edge-shared tetrahedra. They all have linear monomeric gas phase forms.

Beryllium oxide, BeO, is a white, high-melting-point solid, which has the wurtzite structure with a thermal conductivity as high as some metals. BeO is amphoteric. Beryllium hydroxide, Be(OH)2 has low solubility in water and is amphoteric. Salts of beryllium can be produced by reacting Be(OH)2 with acid.

Beryllium sulfide, selenide and telluride all have the zincblende structure.

Beryllium nitride, Be3N2 is a high-melting-point compound which is readily hydrolysed. Beryllium azide, BeN6 is known and beryllium phosphide, Be3P2 has a similar structure to Be3N2.

A number of beryllium borides are known, Be5B, Be4B, Be2B, BeB2, BeB6, BeB12.

Beryllium carbide, Be2C, is a high melting, brick red compound that reacts with water to give methane. No beryllium silicide has been identified.

Basic beryllium nitrate and basic beryllium acetate have similar tetrahedral structures with four beryllium atoms coordinated to a central oxide ion.

Occurrence
See also: Category:Beryllium minerals
The beryllium content of the earth’s surface rocks is ca. 4 - 6 ppm. Beryllium is a constituent of about 100 out of about 4000 known minerals, the most important of which are bertrandite (Be4Si2O7(OH)2), beryl (Al2Be3Si6O18), chrysoberyl (Al2BeO4), and phenakite (Be2SiO4). Precious forms of beryl are aquamarine, bixbite and emerald.

Production
Because of its high affinity for oxygen at elevated temperatures and its ability to reduce water when its oxide film is removed, the extraction of beryllium from its compounds is very difficult. Although electrolysis of a fused mixture of beryllium and sodium fluorides was used to isolate the element in the nineteenth century, the metal's high melting point makes this process more energy intensive than the corresponding production of alkali metals. Early in the twentieth century, the production of beryllium by the thermal decomposition of beryllium iodide was investigated following the success of a similar process for the production of zirconium, however it proved to be uneconomic for volume production.

Beryllium metal did not become readily available until 1957. Currently, most production of this metal is accomplished by reducing beryllium fluoride with magnesium metal. The price on the US market for vacuum-cast beryllium ingots was 338 US$ per pound ($745/kg) in 2001.

BeF2 + Mg → MgF2 + Be