5
B
Boron
10.81
Boron (B)
MetalloidGroup 13Period 2p-block-block
Boron is a metalloid chemical element with symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in both the Solar system and the Earth's crust. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals.
Latin name: Borium
Atomic Number
5
Atomic Mass
10.81 g/mol
Phase (STP)
Solid
Electron Config.
[He] 2s² 2p¹
General
SymbolB
Atomic Number5
Atomic Mass10.81 g/mol
CategoryMetalloid
Group13
Period2
Blockp-block
Electron Configuration[He] 2s² 2p¹
Valence Electrons3
ColourBlack-brown
Appearanceblack-brown
CAS NumberCAS7440-42-8
Physical Properties
Phase (STP)Solid
Density2.08 g/cm³
Melting Point2075.85°C · 3768.53°F · 2349.00 K
Boiling Point3926.85°C · 7100.33°F · 4200.00 K
Atomic Properties
Atomic Radius87 pm
Covalent Radius84 pm
Electronegativity2.04 Pauling
Ionization Energy801 kJ/mol
Electron Affinity26.99 kJ/mol
Oxidation States+1, +2, +3
Ion ChargeB³⁺
Thermodynamic
Molar Heat11.087 J/(mol·K)
Thermal Conductivity27 W/(m·K)
Electromagnetic
Electrical TypeSemiconductor
Crystal Structure
Crystal StructureRhombohedral
Mechanical Properties
Mohs Hardness9.3
Abundance
In Universe0.00001%
In Sun0.0000002%
In Earth's Crust0.1000%
In Oceans0.0004%
In Humans0.00006999999999999999%
In Meteorites0.0016%
Discovery & History
Discovery Year1808
Discovered ByJoseph Louis Gay-Lussac
Isotopes of Boron
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| B-10 | 19.9% | Stable | — |
| B-11 | 80.1% | Stable | — |