Periodic table › Boron
1. Identity and classification
Brittle, crystalline solid with a metallic luster and semiconducting electrical properties
- Name and symbol
- Boron (Boron) · B
- Atomic number
- 5
- Relative atomic weight / mass number
- 10.81 ± 0.02
- Group · period · block
- 13 · 2 · p
- Category
- Metalloid
- State near room temperature
- Solid
- Stable isotopes
- At least one stable isotope
- CAS number
- 7440-42-8
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 5 · 5
- Neutrons in reference isotope
- 6 (11B)
- Full electron configuration
1s² 2s² 2p¹- Abbreviated configuration
[He]2s² 2p¹- Electrons per shell
- 2, 3
- Listed oxidation states
- +3
- Electronegativity
- 2.04 (Pauling)
- First ionization energy
- 800.635 kJ/mol · 8.298 eV
- Electron affinity
- 26.726 kJ/mol
- Covalent radius
- 84 pm
- van der Waals radius
- 192 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 2.37 g/cm³
- Melting point
- 2348 K · 2074.85 °C · 3766.73 °F
- Boiling point
- 4273 K · 3999.85 °C · 7231.73 °F
- Crystal structure
- Rhombohedral
- Specific heat
- 1.026 J/(g·K)
- Thermal conductivity
- 27.4 W/(m·K)
- Enthalpy of fusion
- 50.2 kJ/mol
- Enthalpy of vaporization
- 508 kJ/mol
- Magnetic ordering
- Diamagnetic
- Mohs hardness
- 9.5
- Speed of sound
- 16200 m/s
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The listed electron configuration and oxidation states describe atomic structure; compound properties depend on bonding and composition.
Selected compounds: BO / B₂O₃ (Oxide) · BClₙ (Chloride) · BFₙ (Fluoride)
Reaction reference
Oxidation behavior depends on temperature, surface passivation and the chemical environment.
Direct reaction with water is element- and condition-dependent.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 10B | Stable | 19.65% | Stable |
| 11B | Stable | 80.35% | Stable |
| 12B | Radioactive | — | 20.20 ms |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- 1808 CE
- Scientists associated with discovery
- Joseph Louis Gay-Lussac, Louis Jacques Thénard & Humphry Davy
- Location
- France / UK
- Origin
- Natural
- Listed crustal abundance
- Not established
Minerals and naming reference
Borax, Kernite, Colemanite, Ulexite
Named from scientific/historical roots associated with Boron (B), discovered or characterized by Joseph Louis Gay-Lussac, Louis Jacques Thénard & Humphry Davy.
7. Applications
Borosilicate lab glass (Pyrex), fiberglass insulation, neodymium-iron-boron magnets, nuclear control rods, plant cell-wall micronutrient
Detailed applications by field
- everyday
- Borosilicate lab glass (Pyrex), fiberglass insulation, neodymium-iron-boron magnets, nuclear control rods, plant cell-wall micronutrient
- industry
- Used in metalloid processing, specialized alloys, and chemical manufacturing (Borosilicate lab glass (Pyrex), fiberglass insulation, neodymium-iron-boron magnets, nuclear control rods, plant cell-wall micronutrient).
- electronics
- Applied in electronic components, semiconductors, or functional coatings where Boron's electronic structure ([He] 2s² 2p¹) provides target conductivity.
- medicine
- Diagnostic imaging, biomedical instrumentation, or pharmaceutical synthesis research.
- energy
- Utilized in power generation, battery materials, catalysts, or nuclear technology involving Boron.
- aerospace
- High-performance materials, structural alloys, or space instrumentation utilizing Boron.
- agriculture
- Soil geochemistry analysis, trace micronutrient research, or analytical environmental monitoring.
- science
- Spectroscopic standard, crystallography, and quantum chemistry studies of Period 2 p-block elements.
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Classified as trace element in human and biological systems.