page_title: Period 2 element
section_title: Boron
hierarchical_section_title: Period 2 element / Periodic trends / Boron
context_page_description: A period 2 element is one of the chemical elements in the second row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate/display recurring trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties.
  The second period contains the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the second shell, more specifically its 2s and 2p subshells. Period 2 elements obey the octet rule in that they need eight electrons to complete their valence shell, where at most eight electrons can be accommodated: two in the 2s orbital and six in the 2p subshell.
context_section_description: Boron (B) is the chemical element with atomic number 5, occurring as ¹⁰B and ¹¹B. At standard temperature and pressure, boron is a trivalent metalloid that has several different allotropes. Amorphous boron is a brown powder formed as a product of many chemical reactions. 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. Boron's most common isotope is ¹¹B at 80.22%, which contains 5 protons and 6 neutrons. The other common isotope is ¹⁰B at 19.78%, which contains 5 protons and 5 neutrons. These are the only stable isotopes of boron; however other isotopes have been synthesised. Boron forms covalent bonds with other nonmetals and has oxidation states of 1, 2, 3 and 4.
  Boron does not occur naturally as a free element, but in compounds such as borates. The most common sources of boron are tourmaline, borax, Na₂B₄O₅(OH)₄·8H₂O, and kernite, Na₂B₄O₅(OH)₄·2H₂O. it is difficult to obtain pure boron. It can be made through the magnesium reduction of boron trioxide, B₂O₃. This oxide is made by melting boric acid, B(OH)₃, which in turn is obtained from borax. Small amounts of pure boron can be made by the thermal decomposition of boron bromide, BBr₃, in hydrogen gas over hot tantalum wire, which acts as a catalyst. The most commercially important sources of boron are: sodium tetraborate pentahydrate, Na₂B₄O₇ · 5H₂O, which is used in large amounts in making insulating fiberglass and sodium perborate bleach; boron carbide, a ceramic material, is used to make armour materials, especially in bulletproof vests for soldiers and police officers; orthoboric acid, H₃BO₃ or boric acid, used in the production of textile fiberglass and flat panel displays; sodium tetraborate decahydrate, Na₂B₄O₇ · 10H₂O or borax, used in the production of adhesives; and the isotope boron-10 is used as a control for nuclear reactors, as a shield for nuclear radiation, and in instruments used for detecting neutrons.
  Boron is an essential plant micronutrient, required for cell wall strength and development, cell division, seed and fruit development, sugar transport and hormone development. However, high soil concentrations of over 1.0 ppm can cause necrosis in leaves and poor growth. Levels as low as 0.8 ppm can cause these symptoms to appear in plants particularly boron-sensitive. Most plants, even those tolerant of boron in the soil, will show symptoms of boron toxicity when boron levels are higher than 1.8 ppm. In animals, boron is an ultratrace element; in human diets, daily intake ranges from 2.1–4.3 mg boron/kg body weight (bw)/day. It is also used as a supplement for the prevention and treatment of osteoporosis and arthritis.
caption: Boron chunks
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