Boron
Symbol: B
Atomic Number: 5
Atomic Mass: 10.811 amu (atomic mass units)
Melting Point: 2300.0 C (2573.15 K, 4172.0 F)
Boiling Point: 2550.0 C (2823.15 K, 4622.0 F)
Number of Protons: 5
Number of Electrons: 5
Number of Neutrons: 6
Classification: Metalloid
Crystal Structure: Rhombohedral
Density @ 293 K: 2.34 grams per cubic centimeter
Color: brown/black
Compounds containing the element boron have been known for thousands of years. The pure element was isolated in 1808 by two independent scientists: Sir Humphry Davy in England and Joseph-Louis Gay-Lussac with Louis-Jaques Thenard in France. They both used the same technique for this isolation, the combining of boric acid with potassium. The name boron comes from the Persian word “Burah” and the Arabic “Buraq”, which are the names for the compound borax.
Commercial quality boron is produced by heating borax with carbon. High purity boron can be obtained by the magnesium reduction of boron tri-oxide. The thermal decomposition of compounds, such as boron tri-bromide, with hydrogen using a tantalum wire heated to above 1000C (1273 K, 1832 F) also yields pure boron.
There are two naturally occurring isotopes of boron both are stable. The most common isotope is boron-11, which accounts for 80.2 % of the total. The other natural isotope is boron-10. There are ten man-made isotopes of boron. All these isotopes have extremely short half-lives, the longest half-life being that of boron-8 at 770 milliseconds.
Boron is within group 13 of the periodic table. Group 13 is a group of metalloids or semi-metals. Chemically this group forms a borderline between metals and non-metals. Within this group, boron’s chemical properties are closer to those of silicon rather than indium or gallium. It is a semi-conductor unlike the metals, which freely conduct electricity.
Crystalline boron is an inert material. It will even resist decomposition with boiling hydrochloric or hydrofluoric acids. When finely divided, the element will be attacked, slowly, by hot concentrated nitric acid.
The element has a number of industrial uses.
* In signal flares and pyrotechnic displays, amorphous boron is used to provide a green color.
* It has been used as an ignition source for some rockets.
* Boron-10 is used within the nuclear power industry as it is a good neutron absorber. It is used in the production of control rods for reactors and radiation shields. It is also used as a neutron detector.
* Boron filaments are lightweight and have a high tensile strength. This property has proved useful in the aerospace industry. They are also used in fiber optics research.
In addition, many boron compounds are commercially important.
* Sodium borate pentahydrate is used in the production of fiberglass insulation as well as to make sodium perborate bleach.
* Boric acid is used as a flame retardant, in cellulose insulation and in the production of textile fiberglass. In North America, boric acid is used as a control agent against such insects as cockroaches, fleas and silverfish.
* Borax or sodium borate decahydrate is used as a mild antiseptic and in the production of laundry products. It is also used as a flux in welding.
* Boron hydrides have been used as rocket fuel.
* Other boron compounds are used to produce enamels and borosilicate glass. Such enamels are particularly useful in the coating of the steel casings on refrigerators and washing machines.
Sixth grade students, following Jefferson Lab’s BEAMS science program, experiment with a strange material known as “Oobleck”. Borax is a major constituent of Oobleck.
