Boron (B) – element 5
Boron is a chemical element with the symbol B and atomic number 5. It is a metalloid in group 13, period 2 of the periodic table (p-block), and is a solid at room temperature.
Boron (B) has atomic number 5, atomic mass 10.81 u and electron configuration [He] 2s2 2p1.
Boron facts
| Symbol | B |
|---|---|
| Atomic number | 5 |
| Atomic mass | 10.81 u (g/mol) |
| Category | metalloid |
| Group | group 13 |
| Period | 2 |
| Block | p-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p1 |
| Noble-gas notation | [He] 2s2 2p1 |
| Electrons per shell | 2, 3 |
| Valence electrons | 3 |
Bohr model and shells
Boron has 5 electrons in 2 shells: 2, 3. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 2349 K (2075.8 °C) |
|---|---|
| Boiling point | 4200 K (3926.8 °C) |
| Density | 2.08 g/cm³ |
| Electronegativity (Pauling) | 2.04 |
| Electron affinity | 26.989 kJ/mol |
| Ionization energies | 800.6, 2427.1, 3659.7 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 11.087 J/(mol·K) |
| Discovered by | Joseph Louis Gay-Lussac |
Use the atomic mass in the molar mass calculator for any formula containing B.
Position in the periodic table
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Frequently asked questions
What is the atomic mass of boron?
The atomic mass of boron is 10.81 u, so one mole of boron atoms weighs 10.81 g.
What is the electron configuration of boron?
Boron has 5 electrons: 1s² 2s² 2p¹, or [He] 2s² 2p¹ in noble-gas notation. Electrons per shell: 2, 3.
How many valence electrons does boron have?
Boron has 3 valence electrons (group 13).
Is boron a metal?
Boron is a metalloid: it has properties between metals and nonmetals.
Where is boron on the periodic table?
Boron is in group 13, period 2, in the p-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.