ElementsWhat is boron?
Boron is a hard, dark element that is partly like a metal and partly not. It is never found pure in nature. It is mined as borax and similar minerals from dry lake beds.
What is boron used for?
Heat-resistant borosilicate glass for kitchen and laboratory ware, glass fibre, detergents, and control rods in nuclear reactors.
Where the name comes from
From borax, a mineral salt known and traded for many centuries.
Key facts
- Symbol
- B
- Atomic number
- 5
- Atomic mass
- 10.81 u
- Family
- Metalloid
- Period
- 2
- Group
- 13
- Block
- p
- State at room temperature
- Solid
- Melting point
- 2,075 °C (2,348 K, 3,767 °F)
- Boiling point
- 4,000 °C (4,273 K, 7,232 °F)
- Density
- 2.37 g/cm³
- Electrons per shell
- 2, 3
- Electron configuration
- [He]2s2 2p1
- Common oxidation states
- +3
- Electronegativity (Pauling)
- 2.04
- First ionisation energy
- 8.298 eV
- Electron affinity
- 0.277 eV
- Atomic radius (van der Waals)
- 192 pm
- Discovered
- 1808
Place in the periodic table
Boron is element number 5. It sits in period 2 (row 2) of the periodic table, in group 13 (column 13), and belongs to the p-block. Just before it comes beryllium (4), and just after it comes carbon (6). In the same column, aluminium is below it. Elements in one column tend to behave alike.
Family: Metalloids.
Physical properties
At room temperature boron is a solid. It melts at 2,075 °C and boils at 4,000 °C, so it stays liquid over a range of 1,925 degrees. Its density is 2.37 grams per cubic centimetre, so a one-litre block would weigh about 2.37 kilograms. By density it ranks 73rd among the 96 elements with a measured value.
Inside the atom
An atom of boron has 5 protons in its nucleus and, when neutral, 5 electrons around it. The electrons are arranged in 2 shells: 2, 3. The outermost shell holds 3 electrons. Written in full, the electron configuration is [He]2s2 2p1.
Its electronegativity on the Pauling scale is 2.04. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 8.298 electronvolts (about 801 kilojoules per mole). One mole of boron weighs 10.81 grams, so a single gram contains about 5.57 × 1022 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains boron with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.