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B
5
C
6
Mg
12
Al
13
Si
14

 

Periodic table

 

B
B
Bor

PERIODIC TABLE OF THE ELEMENTS

BORON

BORON GROUP

 

Atomic number:5

Group numbers:13

Period:2

Electronic configuration:[He] 2s2 2p1

Formal oxidation number:+3

Electronegativities:2.04

Atomic radius / pm:79.5

Relative atomic mass:10.811 ± 0.007

 

Boron compounds have been known for thousands of years, but the element was not discovered until 1808 by Sir Humphry Davy (GB) and independently by Joseph-Louis Gay-Lussac and Louis-Jaques Thénard (FR). The origin of the name comes from the Arabic word buraq and the Persian word burah meaning boraks (Na2B4O7*10H2O). It is hard, brittle, lustrous black semimetal. Boron is unreactive with oxygen, water, alkalis or acids. It combines with most metals to form borides. Boron is obtained from kernite, a kind of borax (Na2B4O7*10H2O). High purity boron is produced by electrolysis of molten potassium fluroborate and potassium chloride (KCl). Amorphous boron is used in pyrotechnic flares to provide a distinctive green colour and in rockets as an igniter.

PHYSICAL PROPERTIES

Density / g dm-3:2340 (beta, 293 K)

Molar volume / cm3mol-1:4.62 (beta, 293 K)

Electrical resistivity / μΩcm:1.8E+12 (20 °C)

THERMAL PROPERTIES

Thermal conductivity / W m-1K-1:27

Melting point / °C:2075

Boiling point / °C:4000

Heat of fusion / kJ mol-1:22.2

Heat of vaporization / kJ mol-1:504.5

Heat of atomization / kJ mol-1:557.64

IONIZATION ENERGIES

First ionization energy / kJ mol-1:800.64

Second ionization energy / kJ mol-1:2427.09

Third ionization energy / kJ mol-1:3659.78

ABUNDANCE OF ELEMENTS

in the atmosphere / ppm:-

in the Earth's crust / ppm:10

in the oceans / ppm:4.8

CRYSTALLOGRAPHIC DATA

rhombohedral

Crystal structure:

rhombohedral

Unit-cell dimensions / pm:

a=506.7, α=58°4'

Space group:

R3m

ISOTOPES

IsotopeRelative atomic massMass percent (%)
10B10.0129370(3)19.9(2)
11B11.0093055(5)80.1(2)

REDUCTION POTENTIALS

Balanced half-reaction Eo / V
H3BO3 + 3H+ + 3e- = B(s) + 3H2O- 0.869
H2BO3- + 4H+ + 3e- = B(s) + 3H2O- 0.687
HBO32- + 5H+ + 3e- = B(s) + 3H2O- 0.437
BO33- + 6H+ + 3e- = B(s) + 3H2O- 0.165
B(OH)3 + 3H+ + 3e- = B(s) + 3H2O- 0.87
BF4- + 3e- = B(s) + 4F-- 1.04
H2B4O7 + 12H+ + 12e- = 4B(s) + 7H2O- 0.836
B4O72- + 14H+ + 12e- = 4B(s) + 7H2O- 0.792

 

4 Beryllium <=
5 Boron
=> 6 Carbon