Boron (B)

Black-brown metalloid

Boron is a hard, dark metalloid found in detergents and heat-resistant glass, and with the electron configuration [He] 2s² 2p¹, boron forms complex covalent networks and icosahedral clusters. It is essential for plant cell walls and has the third-highest hardness of any element.

Key metrics

Density2.34g/cm³

Melting point2,349K

Boiling point4,200K

Electronegativity2.04Pauling

Discovery

1808discovered

Discovered by: Joseph Louis Gay-Lussac
Reactivity profile: Low at room temperature
Reactivity: Medium
Bonding: Covalent

Electron configuration

\textcolor{#6b7280}{[He]}\; \textcolor{#ef4444}{2_{s}^{2}}\; \textcolor{#3b82f6}{2_{p}^{1}}

[He] 2s2 2p1

Wave function

\Psi_{\text{B}} \approx \frac{1}{\sqrt{5!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_5(\mathbf{r}_5) \right|

Probability density $|\Psi|^2$ across the B valence shell.

Crystal structure

Rhombohedral

Lattice constantsa 1.00 · b 1.00 · c 1.00

Cell anglesα = β = γ = 61.5°

Coordination number—

Atoms per cell—

Atomic packing factor0.53

Physical properties

Atomic radius: 87 pm
Ionization energy: 801 kJ/mol
Electron affinity: 27 kJ/mol
Crystal structure: Rhombohedral

Oxidation states

Acid/base

Acidic

Strongly acidicStrongly basic

State at 25 °CSolid

2349 K4200 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

249.7nmB I (UV)UV100%

249.8nmB I (UV)UV90%

583.4nmB IYellow30%

Dominant line 249.7 nmRange 250–583 nmTransitions 3