Periodic Table


Atomic number: 5
Atomic weight: 10.811
Symbol: B
Group number: 13
Electronic configuration: [He].2s2.2p1


Boron is a Group 13 element. Boron has properties which are borderline between metals and non-metals. It is a semiconductor rather than a metallic conductor. Chemically it is more related to silicon than to aluminium, gallium, indium, and thallium.

Crystalline boron is inert chemically and is resistant to attack by boiling HF or HCl. When finely divided it is attacked slowly by hot concentrated nitric acid.

General information

Discoveror: Sir Humphrey Davy, Joseph-Louis Gay-Lussac, Louis-Jaques Thénard
Date discovered: 1808
Discovered at: England, France
Meaning of name: From the Arabic word "buraq" and the Persian word "burah"

Physical data

Standard state: solid at 298 K
Colour: black
Density of solid at ambient temperature/kg m-3: 2460
Molar volume/cm3: 4.39

Radii /pm

Atomic: 87
Covalent (single bond):
Pauling radius for the ion [B]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius80.783.9no datano data


Both values are quoted on the Pauling scale.

Pauling: 2.04
Allred Rochow: 2.01

Crystal Structure

structure: rhombohedral

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 2349
boiling point: 4200

Enthalpies /kJ mol-1

fusion: 50.2
vaporization: 507

single bond enthalpies:
B-F B-Cl B-Br B-I B-B
613 456 377 no data 297

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
10B10.0129369 (3)19.9 (2)
11B11.0093054 (4)80.1 (2)

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/B.html