|Name: boron||Group number: 13|
|Symbol: B||Group name: (none)|
|Atomic number: 5||Period number: 2|
|Atomic weight: 10.811 (7) g m r||Block: p-block|
|CAS Registry ID: 7440-42-8||Voice: |
|Standard state: solid at 298 K||Colour: black|
|Classification: Semi-metallic||Availability: |
Image adapted with permission from Prof James Marshall"s (U. North Texas, USA) Walking Tour of the elements CD.
Boron is a Group 13 element. Boron has properties which are borderline between metals and non-metals. 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.
Nearing Zero cartoon included by kind permission of Nick Kim.
IsolationHere is a brief summary of the isolation of boron.
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.