Boron

Boron: the essentials

 Brief description: boron is a Group 13 element that has properties which are borderline between metals and non-metals (semimetallic). It is a semiconductor rather than a metallic conductor. Chemically it is closer to silicon than to aluminium, gallium, indium, and thallium.

Crystalline boron is inert chemically and is resistant to attack by boiling HF or HCl. When finely divided it is attacked slowly by hot concentrated nitric acid.

Image adapted with permission from Prof James Marshall's (U. North Texas, USA) Walking Tour of the elements CD.

Cartoon by Nick D Kim (nearingzero.net, used by permission).

Isolation

Isolation: it is not normally necessary to make boron in the laboratory and it would normally be purchased as it is available commercially. 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. It can be made through the magnesium reduction of the oxide, B₂O₃. The oxide is made by melting boric acid, B(OH)₃, which in turn is obtained from borax.

B₂O₃ + 3Mg → 2B + 3MgO

Samm amounts of high purity boron are available through the thermal decomposition of compounds such as BBr₃ with hydrogen gas using a heated tantalum wire. Results are better with hot wires at tmeperatures over 1000°C.

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