Boron (B)
Element 5 · Metalloid · atomic mass 10.81 u · group 13, period 2
Electron shells: 2, 3
Boron is a metalloid that sits on the staircase between metals and non-metals, forming unusual electron-deficient structures. It is an essential plant nutrient, needed for cell-wall integrity.
Boron-10 absorbs neutrons so greedily that it is used to shut down nuclear reactors.
- Atomic number
- 5
- Atomic mass
- 10.81 u
- Electron configuration
- [He] 2s² 2p¹
- Group · period · block
- 13 · 2 · p
- Oxidation states
- +3
- Electronegativity
- 2.04 (Pauling)
- Melting point
- 2,075 °C
- Boiling point
- 4,000 °C
- Density
- 2.37 g/cm³
- State at 20 °C
- Solid
- Appearance
- Black-brown, brittle semi-metal
- Discovered
- Humphry Davy, Joseph Louis Gay-Lussac and Louis Jacques Thénard, 1808
5 protons, and 5 electrons when neutral
IUPAC interval [10.806, 10.821]
Boron group
What Boron is used for
- Borosilicate glass and glass fibre
- Detergents and bleaches
- Neutron-absorbing control rods
- Fertiliser micronutrient
Atomic structure of Boron
A neutral boron atom has 5 protons and 5 electrons. Its most common isotope carries about 6 neutrons, which is where the mass number 11 comes from. Change the neutron count and you have a different isotope of boron; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 3. In orbital notation that is [He] 2s² 2p¹, leaving 3 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Boron's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Boron sits in the periodic table
Discovery and naming
Boron was discovered by Humphry Davy, Joseph Louis Gay-Lussac and Louis Jacques Thénard in 1808. Its name comes from Arabic buraq, "borax".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Boron?
The standard atomic weight of Boron is 10.81 u. Because the natural isotope mix varies between sources, IUPAC publishes it as the interval [10.806, 10.821], and 10.81 is the conventional single value to use in calculations.
How many protons, neutrons and electrons does Boron have?
Boron has 5 protons, because the atomic number is the proton count and that is what makes an atom Boron at all. A neutral Boron atom has the same number of electrons, 5. The neutron count varies by isotope; the most common one has about 6, since 11 − 5 = 6.
What is the electron configuration of Boron?
The electron configuration of Boron is [He] 2s² 2p¹. Its electrons are arranged 2, 3 across 2 shells.
Is Boron a metal?
Not quite. Boron is a metalloid — it sits on the staircase dividing metals from non-metals and shows properties of both, which is exactly why metalloids matter to the semiconductor industry.
What group and period is Boron in?
Boron is in group 13 (the boron group), period 2, in the p-block. The group is its column and the period is its row.
What is the charge of Boron?
Boron most commonly forms a 3+ ion. It has 3 outer electrons available to lose.
What is the melting point of Boron?
Boron melts at 2,075 °C and boils at 4,000 °C. That puts it in the solids at everyday temperatures.
What is Boron used for?
Borosilicate glass and glass fibre, Detergents and bleaches, Neutron-absorbing control rods, Fertiliser micronutrient. Boron is a metalloid that sits on the staircase between metals and non-metals, forming unusual electron-deficient structures.
Who discovered Boron, and where does its name come from?
Boron (B) was discovered by Humphry Davy, Joseph Louis Gay-Lussac and Louis Jacques Thénard in 1808. The name comes from Arabic buraq, "borax".