Boron (B)

Boron (symbol B) is the chemical element with atomic number 5: a metalloid, solid at 0 °C, with an atomic mass of 10.81 u. Discovered in 1808 (Joseph Louis Gay-Lussac, Louis Jacques Thénard and Humphry Davy).

Boron is a metalloid, halfway between metals and nonmetals. Little known to the public, it is everywhere: in glass wool, ovenproof glass dishes, detergents and the magnets of electric motors. It is also essential for plant growth. Its boron-10 form absorbs neutrons, making it a guardian of nuclear reactors.

Key facts

Atomic number: 5
Symbol: B
French name: Bore
Atomic mass: 10.81 u
Molar mass: 10.81 g/mol
Family: Metalloids
Position: period 2, group 13, p-block
State at 0 °C: Solid
Melting point: 2,075.9 °C
Boiling point: 3,926.9 °C
Density: 2.34 g/cm³
Electronegativity (Pauling): 2.04
First ionization energy: 801 kJ/mol
Atomic radius: 85 pm
Electron configuration: [He] 2s² 2p¹
Abundance in Earth's crust: 10 ppm (37th most abundant element)
Indicative price: 4 $/kg (order of magnitude)
Radioactive: no
Discovery: 1808, Joseph Louis Gay-Lussac, Louis Jacques Thénard and Humphry Davy

Origin of the name

From borax, via the Arabic buraq.

What does boron look like?

When pure, a shiny black and extremely hard solid in crystalline form, or a brown powder in amorphous form.

Where is boron found?

About 10 ppm of Earth's crust. It is concentrated in borate deposits formed by the evaporation of ancient lakes in volcanic and desert regions, such as Turkey or California (Death Valley).

Natural sources

Borax
Kernite
Colemanite
Ulexite

How is boron produced?

Borates are mined in open pits, then refined into boric acid or borax. Pure boron, little used, is obtained by chemical reduction at high temperature. Several million tonnes of boron minerals are produced each year; Turkey holds about 70% of world reserves.

Top producers

Turkey
United States
Chile
China

What is boron used for?

Glass wool and fiberglass for insulation.
Heat-resistant borosilicate glass (Pyrex-type).
Neodymium-iron-boron magnets in electric motors and wind turbines.
Fertilizers for boron-deficient crops.
Control rods in nuclear reactors.
Boron carbide for bulletproof vests.

In everyday life

An ovenproof glass dish
Glass-wool insulation in the attic
The magnets in earbuds and hard drives
Some laundry detergents and household cleaners

Role in living things

Essential to plants, where it strengthens cell walls; a deficiency makes beets, rapeseed or grapevines wither. In humans it is present in traces (from fruit and vegetables), but whether it is truly essential has not been established.

Hazards of boron

Of low toxicity in small amounts. However, the European Union classifies boric acid and borax as toxic to reproduction at high exposure, which has restricted their use in consumer products.

Cosmic origin

Cosmic rays: Born from the fragmentation of heavier atoms struck by high-energy particles.

History of boron

Borax has been known since antiquity, notably to Asian goldsmiths who used it as a flux. In 1808, Joseph Louis Gay-Lussac and Louis Jacques Thénard in France, and Humphry Davy in England, independently isolated impure boron. Truly pure boron was not obtained until the 20th century.

Did you know?

Ulexite, nicknamed “TV rock,” is made of natural fibers that carry light: set it on a printed page and the text seems to appear on its surface.
Boron carbide is one of the hardest materials known, after diamond and cubic boron nitride.
The green flash in fireworks can come from boron compounds (or barium).

Isotopes of boron

Two stable isotopes. Boron-10 is one of the best neutron “traps” there is, which gives it a key role in nuclear safety.

boron-10: 19.9% of natural boron, stable. Neutron absorber in reactor control rods and in boron neutron capture cancer therapy.
boron-11: 80.1% of natural boron, stable. Used in pure form in semiconductors, since it doesn't turn radioactive under neutron bombardment.

Common compounds

Neodymium magnet (Nd₂Fe₁₄B)

Related elements

Same family (metalloids): Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te).

Same column (group 13): Aluminium (Al), Gallium (Ga), Indium (In), Thallium (Tl), Nihonium (Nh).