Boron (B)
[He] 2s² 2p¹. 1 unpaired electron, period 2, group 13, p block.
Element or ion
Type a symbol, a name or an atomic number, add a charge such as Fe3+ or Cl-, or tap an element in the table. Orbitals fill from m = −l up, spin +½ first.
BBoron, Z = 5, 10.81 u
[He] 2s2 2p1
In full: 1s² 2s² 2p¹
- Blockp block
- Period2
- Group13
- Valence3
- Unpaired1
- MagneticPara
Last electron 2p
- n2shell
- l1p subshell
- m−1orbital
- s+½spin up
Step by step
- Boron has 5 electrons.
- Fill in (n + l) order: 1s² 2s² 2p¹.
- Write the subshells in order of n: 1s² 2s² 2p¹.
- Replace the helium core with [He]: [He] 2s² 2p¹.
Boron (B): the numbers
| Atomic number | 5 |
|---|---|
| Atomic mass | 10.81 u |
| Period | 2 |
| Group | 13 |
| Block | p block |
| Valence electrons | 3 |
| Unpaired electrons | 1 |
| Magnetic | paramagnetic |
| Last electron | 2p: n = 2, l = 1, m = −1, s = +1/2 |
Boron (B): quick answers
What is the electronic configuration of boron?
Boron has 5 electrons: 1s² 2s² 2p¹, or [He] 2s² 2p¹ in short.
How many unpaired electrons does boron have?
Boron has 1 unpaired electron, so it is paramagnetic. Put one electron in each box of a subshell before pairing (Hund’s rule) to see them.
What are the quantum numbers of the last electron of boron?
The last electron goes into 2p: n = 2, l = 1, m = −1, s = +1/2. Orbitals fill from m = −l up, spin +½ first.