Boron
Atomic Data
| Atomic Number | 5 |
| Symbol | B |
| Atomic Weight | 10.81 u |
| Density (STP) | 2.34 g/cm³ |
| Melting Point | 2075.85 °C (2349 K) |
| Boiling Point | 3926.85 °C (4200 K) |
| Electronegativity | 2.04 (Pauling) |
| Electron Config. | 1s2 2s2 2p1 |
| Oxidation States | +3 |
| Phase at STP | Solid |
| Category | Metalloid |
| Period / Group | 2 / 13 |
| CAS Number | 7440-42-8 |
Electron Configuration
[He] 2s2 2p1
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 1 | 5 |
| Total | 5 | 5 | ||
Abundance & Occurrence
Boron is present in Earth's crust at approximately 10 ppm by mass and at approximately 1 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Dust inhalation: Fine boron powder and boron compound dusts are respiratory irritants; prolonged inhalation of high concentrations may cause nose, throat, and lung irritation.
- Skin and eye irritation: Boron compounds (especially borax and boric acid) cause mild skin and eye irritation on prolonged contact; boric acid powder should not be applied to broken skin or open wounds.
- Reproductive toxicity: High-dose exposure to boric acid is toxic to reproduction; it is classified as a Category 1B reproductive toxicant in the EU and should not be handled by pregnant individuals without strict controls.
- Boron hydrides (boranes): Diborane (B2H6) and other boranes are highly toxic, flammable, and can detonate in air; they require specialised handling under inert gas with appropriate gas detection.
Boron in the Real World
Real-World Uses
- Borosilicate glass — Boron oxide is a key component of borosilicate glass (sold as Pyrex and Duran), which resists thermal shock and is used in laboratory glassware, cookware, and pharmaceutical packaging.
- Detergents — Sodium perborate and sodium tetraborate (borax) are oxygen-releasing bleaching agents and water softeners in laundry detergents, dishwasher powders, and hand soaps.
- Semiconductor doping — Boron is the primary p-type dopant in silicon integrated circuits; adding trace boron creates positive charge carriers (holes) that are essential for transistors and diodes.
- Nuclear reactor control rods — Boron-10 has a very high neutron capture cross-section; boron carbide (B₄C) pellets are used in control rods to regulate fission reactions in nuclear power plants.
- High-strength fibres — Boron fibres and boron carbide composites are used in lightweight armour panels, golf club shafts, and aerospace structural components requiring extreme stiffness.
- Neodymium magnets — Boron is an essential component of Nd-Fe-B permanent magnets, the strongest type of permanent magnet used in electric motors, wind turbines, hard drives, and loudspeakers.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is boron used for?
Boron has many uses: boron oxide is a key ingredient of borosilicate glass (Pyrex) used in cookware and labware; sodium borate (borax) is used in laundry detergents and as a cleaning agent; boron is a critical p-type dopant in silicon semiconductors; boron carbide is used in nuclear reactor control rods; and boron is an essential component of the strongest permanent magnets (Nd-Fe-B).
Is boron a metal or non-metal?
Boron is a metalloid (also called a semimetal). At room temperature it exists as a dark, lustrous solid with electrical conductivity between that of metals and insulators, and it exhibits both metallic and non-metallic chemical behaviour depending on the reaction. Its most common solid forms are amorphous and crystalline polymorphs with complex icosahedral (B₁₂) cluster structures.
Is boron essential for life?
Boron is an essential micronutrient for plants, where it plays a critical role in cell wall formation, sugar transport, and reproductive development. Boron deficiency causes growth abnormalities including hollow stem in brassicas and poor fruit set in many crops. In animals and humans, boron appears to support bone health, immune function, and cognitive performance, though it has not been definitively classified as essential for mammals.
Where does boron come from?
Boron is found naturally as borax (sodium tetraborate) and kernite mineral deposits, primarily in arid lake-bed evaporite formations. The largest reserves are in Turkey (which produces about 70% of the world’s boron) and the United States (California). Boron minerals are soluble in water and were deposited by the evaporation of ancient inland seas and volcanic hydrothermal activity.