Boron (B)
Boron is element 5, a metalloid in period 2, group 13 of the periodic table. At room temperature it is a solid.
Electron configuration [He] 2s2 2p1
Electrons per shell 2, 3
Boron data
| Atomic number | 5 |
|---|---|
| Symbol | B |
| Atomic mass | 10.811 u |
| Category | Metalloid |
| Group | 13 |
| Period | 2 |
| Block | p |
| State at 25 °C | solid |
| Melting point | 2348 K (2074.9 °C) |
| Boiling point | 4273 K (3999.9 °C) |
| Density | 2.46 g/cm³ |
| Electronegativity (Pauling) | 2.04 |
| Atomic radius | 82 pm |
| 1st ionization energy | 801 kJ/mol |
| Electron affinity | -27 kJ/mol |
| Oxidation states | +1, +2, +3 |
| Common ion charge | 3+ |
| Discovered | 1807 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through boron’s configuration and its ions →
Where boron sits
Boron belongs to the metalloids. Its Pauling electronegativity of 2.04 is mid-range; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Boron FAQ
What is the electron configuration of boron?
Boron (Z = 5) has the configuration 1s2 2s2 2p1. In noble-gas shorthand that is [He] 2s2 2p1.
How many valence electrons does boron have?
3 (outer shell (n = 2)).
What is the atomic mass of boron?
The standard atomic weight of boron is 10.811 u, so one mole weighs 10.811 g.
Is boron a metal?
Boron is a metalloid: it has properties between metals and nonmetals.
What is the charge of a boron ion?
Boron most commonly forms B3+.