Boron (B)
Metalloid
Boron is a metalloid that behaves like neither a clear metal nor a nonmetal. It forms extremely hard compounds, strengthens glass against heat shock, and is essential for plant growth.
Position on the periodic table
Atomic properties
| Atomic number | 5 |
|---|---|
| Atomic mass | 10.81 amu |
| Electron configuration | 1s2 2s2 2p1 |
| Noble gas shorthand | [He] 2s2 2p1 |
| Electrons per shell | 2, 3 |
| Valence electrons (outer shell) | 3 |
| Common oxidation states | +3 |
| Electronegativity (Pauling) | 2.04 |
| Covalent radius (approx.) | 84 pm |
| First ionization energy | 800.6 kJ/mol |
| Electron affinity | 27 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 2.08 g/cm³ |
| Melting point | 2075.8 °C (2349 K) |
| Boiling point | 3926.8 °C (4200 K) |
| Appearance | black-brown |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of boron
Boron's ground-state electron configuration is 1s2 2s2 2p1, usually shortened to [He] 2s2 2p1. Its electrons occupy 2 shells (2, 3), placing it in period 2 of the p-block. The 3 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of boron
- Borosilicate laboratory glassware (heat-resistant glass)
- Fibreglass insulation
- Detergents and cleaning products (borates)
- Neutron-absorbing control rods in nuclear reactors
Biological role: Essential micronutrient for plants; its role in humans is still being studied.
Occurrence: Found in borate minerals such as borax, mainly in evaporated lake deposits.
Common compounds of boron
H3BO3
Boric acid
Na2B4O7
Borax (sodium tetraborate)
B2O3
Boron trioxide
History and discovery
Discovered: 1808 — Joseph Louis Gay-Lussac. Name origin: From borax, the mineral it was isolated from (Arabic buraq).
Isolated in 1808 by Humphry Davy in England and, independently, by Gay-Lussac and Thénard in France.
Safety notes
Boric acid and borates are harmful if swallowed in quantity; ordinary borosilicate glass is completely safe.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Boron
1. What is the chemical symbol of Boron?
2. What is the atomic number of Boron?
3. Which category does Boron belong to?
4. What is the state of Boron at room temperature?
5. Which period of the periodic table is Boron in?
Boron FAQs
What is the atomic number of boron?
Boron's atomic number is 5 — every boron atom has 5 protons in its nucleus.
What is the symbol for boron?
B. From borax, the mineral it was isolated from (Arabic buraq).
Is boron a metal, nonmetal, or metalloid?
Boron is classified as a metalloid — an element with properties between metals and nonmetals.
What state is boron at room temperature?
At about 25 °C, boron is a solid. It melts at 2075.8 °C.
How many valence electrons does boron have?
Boron has 3 electrons in its outer shell (shell pattern: 2, 3).
What is boron used for?
Key uses include: borosilicate laboratory glassware (heat-resistant glass); fibreglass insulation; detergents and cleaning products (borates).
Related elements
Keep working with this element
Spotted an error? Report a correction · Data sources