Stable Isotopes of Boron
|Isotope||Atomic Mass||Natural Abundance||Nuclear Spin||Nuclear Magnetic Moment|
Boron was discovered in 1808 by Sir Humphry Davy, Joseph Louis Gay-Lussac and Louis Jacques Thénard. Its name derives from the Arabic word buraq or the Persian word burah, both of which are names for the mineral borax.
Boron is a nonmetallic element, either a black, hard solid or a brown, amorphous powder. It is one of the least reactive elements on the periodic table; it does not react with water at ambient temperatures, although the powdered amorphous form reacts slowly at 100 ºC, producing boric acid. It reacts vigorously with concentrated nitric acid and ignites in oxygen at 700 ºC.
The amorphous boron metal reacts slowly with dilute mineral acids at ambient temperatures. Boron also reacts with halogens to form boron halides, instantaneously with fluorine but at elevated temperatures with other halogens (chlorine, bromine and iodine, at 400 ºC, 600 ºC, and 900 ºC respectively).
Enriched boron is used in radiation shielding and is the primary nuclide used in neutron capture therapy of cancer. Boron-10 is used in nuclear reactors for reactivity control and in emergency shutdown systems. Boric acid is added to reactor coolant when the plant is shut down for refueling. Boron-10 and -11 are of use in nuclear magnetic resonance (NMR) spectroscopy.
In its elemental form, boron is nontoxic — it is actually a plant micronutrient. Rubbing the amorphous powder on the skin, however, can produce irritation. Some compounds of boron are poisonous.
Properties of Boron
|Standard state||Solid at 298 °K|
|CAS Registry ID||7440-42-8|
|Group in periodic table||13|
|Period in periodic table||2|
|Block in periodic table||p-block|
|Melting point||2075 °C|
|Boiling point||2550 °C|
|Vaporization point||4000 °C|
|Thermal conductivity||0.274 W/(m·K) at 298.2 °K|
|Electrical resistivity||1.8 x 1012 µΩ·cm at 0 ºC; 3.0 x 106 Ω·cm at 100 ºC|
|Specific heat||1030 J/(kg·K)|
|Heat of vaporization||507 kJ·mol-1 at 2550 ºC|
|Heat of fusion||50 kJ·mol-1|
|Density of solid||2.34 cryst. g/cm3|
|Density of powder||2.45 g/cm3|
|Mohs hardness scale||9.3|
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