Boron: the essentials
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.
Boron: historical information
Boron compounds have been known for thousands of years, but the element was not isolated until 1808 by Sir Humphry Davy, Joseph-Louis Gay-Lussac (1778-1850) and Louis Jaques Thenard (1777-1857). This was accomplished through the reaction of boric acid (H3BO3) with potassium.
Boron around us Read more »
Boron is probably not required in the diet of humans but it might be a necessary "ultratrace" element. Boron is required by green algae and higher plants.
Boron is not found free in nature. It occurs usually as orthoboric acid in some volcanic spring waters and as borates in borax and colemanite. Ulexite is interesting as it is a natural fibre optic.
|Location||ppb by weight||ppb by atoms||Links|
|Human||700 ppb by weight||410 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 2349 [2076 °C (3769 °F)] K
- Boiling point: 4200 [3927 °C (7101 °F)] K
- Enthalpy of fusion: |203| kJ mol-1
Crystal structure Read more »
The solid state structure of boron is: rhombohedral.
Boron: orbital properties Read more »
Boron atoms have 5 electrons and the shell structure is 2.3. The ground state electronic configuration of neutral Boron is [He].2s2.2p1 and the term symbol of Boron is 2P1/2.
- Pauling electronegativity: 2.04 (Pauling units)
- First ionisation energy: 800.6 kJ mol‑1
- Second ionisation energy: 2427.1 kJ mol‑1
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.
Boron isotopes Read more »
Both isotopes of Boron, B-10 and B-11, are used extensively in the nuclear industry. B-10 is used in the form of boric acid as a chemical shim in pressurized water reactors while in the form of sodium pentaborate it is used for standby liquid control systems in boiling water reactors. B-11 can be used as a neutron reflector. Outside the nuclear industry both isotopes are used as food label to study boron metabolism. B-10 is also used in so-called boron neutron capture therapy (BNCT). Both B-10 and B-11 can be used for the production of two radioisotopes: C-11 and N-13.
|10B||10.012 937 0(4)||19.9 (7)||3||1.80065|
|11B||11.009 305 5(5)||80.1 (7)||3/2||2.688637|