Boron Element Properties
Complete reference for Boron (B, element 5): atomic data, electron configuration, isotopes, physical constants, and chemical behavior.
Use the Boron Element Properties
Boron
Metalloid — Period 2, Group 13
Atomic Identity
Electron Configuration
One unpaired 2p electron — weakly paramagnetic
Isotopes of Boron
| Isotope | Symbol | Protons | Neutrons | Mass (u) | Natural Abundance | Stability |
|---|---|---|---|---|---|---|
| Boron-8 | ⁸B | 5 | 3 | 8.02461 | Radioactive |
Unstable
β⁺ decay, t½ = 770 ms |
| Boron-10 | ¹⁰B | 5 | 5 | 10.01294 | 19.9% | Stable |
| Boron-11 | ¹¹B | 5 | 6 | 11.00931 | 80.1% | Stable |
| Boron-12 | ¹²B | 5 | 7 | 12.01435 | Radioactive |
Unstable
β⁻ decay, t½ = 20.2 ms |
| Boron-13 | ¹³B | 5 | 8 | 13.01779 | Radioactive |
Unstable
β⁻ decay, t½ = 17.4 ms |
Physical Properties
Chemical Properties
Ground State Quantum Numbers
Notable Emission Lines
Boron compounds can produce a distinctive green flame associated with excited boron oxide species, especially BO₂. When a boron compound is tested with methanol, volatile trimethyl borate can also contribute to the green flame. Its strongest spectroscopic lines lie in the ultraviolet range.
Key Facts About Boron
Electron-Deficient Lewis Acid
Boron has only three valence electrons and forms three bonds in most compounds, leaving an empty p orbital. This makes boron compounds (like BF₃ and BCl₃) strong Lewis acids that readily accept electron pairs. This property is central to boron's role in organocatalysis and synthesis.
Neutron Capture in Nuclear Engineering
Boron-10 has a thermal neutron absorption cross-section of approximately 3,840 barns — among the highest of any stable nuclide. Control rods made from boron carbide (B₄C) and borated water systems are critical safety components in nuclear reactors worldwide.
Extreme Hardness
Boron carbide (B₄C) has a Vickers hardness exceeding 30 GPa, making it the third-hardest known material after diamond and cubic boron nitride (c-BN). It is used in ballistic armor, abrasive grinding wheels, and nuclear shielding. Cubic boron nitride rivals diamond in hardness for industrial cutting tools.
Essential Plant Micronutrient
Boron is an essential micronutrient for plants; it stabilizes cell walls and is critical for pollen germination, fruit development, and sugar transport. Boron deficiency causes "hollow heart" in beets and stunted growth in many crops. Borax is widely used in agriculture as a boron fertilizer supplement.
Boron Neutron Capture Therapy (BNCT)
BNCT is a cancer treatment that selectively delivers boron-10 compounds to tumor cells. When irradiated with thermal neutrons, the ¹⁰B(n,α)⁷Li reaction releases high-energy alpha particles that destroy the tumor cell from within while largely sparing surrounding healthy tissue.
Borax and Industrial Chemistry
Borax (Na₂B₄O₇·10H₂O) is one of the oldest known boron compounds. It serves as a flux in metallurgy, a cleaning agent, a fire retardant, and a precursor to borosilicate glass (Pyrex). The Mojave Desert's Death Valley and Turkey's Kirka mine are the world's largest borax deposits.
Summary
Boron is a metalloid with atomic number 5 and symbol B. It sits at the boundary between metals and nonmetals on the periodic table and exhibits both covalent and ionic bonding behavior. Boron is essential in chemistry for its electron-deficient compounds, in materials science for its extreme hardness, and in nuclear engineering for its high neutron-capture cross-section. This reference compiles the essential physical constants, quantum numbers, isotope data, and distinctive properties of boron in one convenient place.
How it works
- Browse the atomic identity section for symbol, atomic number, and standard atomic weight.
- Check the electron configuration panel for orbital notation and quantum numbers.
- Review the isotopes table for boron-10 and boron-11 data including natural abundance.
- Consult the physical properties panel for melting point, density, and state at STP.
- Use the chemical properties section to understand metalloid behavior and ionization energies.
- Copy any value with one click for use in reports or calculations.
Use cases
- Look up boron constants for chemistry homework or exams.
- Verify atomic data when writing lab reports.
- Reference isotope masses for nuclear chemistry or neutron capture research.
- Check thermodynamic constants for materials science or engineering.
- Teach or learn metalloid properties using boron as a key example.
- Confirm electron configuration before writing molecular orbital diagrams.
- Compare boron-10 and boron-11 for nuclear medicine or spectroscopy research.
- Quick-reference ionization energy for electrochemistry or spectroscopy work.