Boron

Symbol: B
Atomic number: 5
Category: metalloids
Group: 13
Period: 2
Block: p
Atomic weight: 10.811 g/mol
Electrons per shell: 2, 3
CAS number: 7440-42-8
Phase: solid
Density: 2.08 kg/dm³ (near room temperature)
Melting point: 2349 K (2076 °C, 3769 °F)
Boiling point: 4200 K (3927 °C, 7101 °F)
Crystal structure: rhombohedral
Oxidation states: 4, 3, 1
Electronegativity: 2.04 (Pauling scale)
Name's origin: buraq or burah
Name's meaning: the Arabic and Persian words for the mineral borax
Facts:
- occurs abundantly in the evaporite ores borax and ulexite
- several allotropes of boron exist; amorphous boron is a brown powder, though crystalline boron is black, extremely hard (9.3 on Mohs' scale), and a weak conductor at room temperature
- is used as a dopant in the semiconductor industry, while boron compounds play important roles as light structural materials, insecticides and preservatives, and reagents for chemical synthesis
- is an essential plant nutrient, although high soil concentrations of boron may also be toxic to plants
- elemental boron is nontoxic and common boron compounds such as borates and boric acid have low toxicity (approximately similar to table salt with the lethal dose being 2 to 3 grams per kilogram) and therefore do not require special precautions while handling
- nearly all boron ore extracted from the Earth is destined for refinement into boric acid and sodium tetraborate