The Boron Element

 

Represented with B in the periodic table, boron is a semiconductor with atomic number of 5 and atomic mass of 10.81. It is the first and the lightest element of group 3A in the periodic table. Boron's basic electronic configuration is 1s2 2s2 2p1.

Boron is composed of the 8B, 10B, 11B , 12B, 13B isotopes. Its most stable isotopes are 10B and 11B. These isotopes are found in nature at a rate of 19.1-20.3% and 79.7-80.9% respectively. The isotope 10B has a great neutron capture ability. Hence, it can be employed in nuclear supplies and nuclear power plants. Turkey hosts boron ore deposits with high isotope 10B content.

Distinguished properties of boron compounds produced with various metal or non-metal elements provide a vast field of application in a plenitude of industries. In its compounds, boron acts like a non-metal compound, however as a distinctive property, pure boron is an electrical conductor like carbon. Crystallized boron is similar to diamond in terms of appearance and optical characteristics, and is almost as rigid as diamond.
The pure boron element was obtained for the first time by French chemists, J.L. Gay-Lussac and Baron L.J. Thenard, in 1808, and by the English chemist H. Davy.

Boron is found in various allotropic forms. Of them, one is amorphous and six are crystalline polymorphous. Alpha and beta rhombohedral forms represent top crystalline polymorphs under study. Alpha rhombohedral structure decomposes above 1200°C and forms the beta rhombohedral structure form at 1500°C. Amorphous form converts into beta rhombohedral c.a. above 1000°C and all types of pure boron transform into beta rhombohedral form when heated above its melting point and recrystallized.

Boron is ranked 51st among the elements commonly found in the earth crust. Boron never appears as a free element in nature. Almost 230 types of boron minerals are known to be present in nature. One of the most commonly found boron mineral in nature is tourmaline , a kind of aluminoborosilicate mineral with a boron content up to 10%. However, in industry, tincal (Na4B4O2. 10H2O), kernite (Na2B4O7. 4H2O), colemanite (Ca2B6O11. 5H2O) and ulexite (NaCaB5O9. 8H2O) as alkali and alkaline boron minerals are employed. Commercial mine deposits are limited and predominant in Turkey and USA.

The morphology and grain size are decisive in the chemical properties of boron. While amorphous boron of micron size reacts easily and sometimes intensely, crystalline boron is reluctant to react. Boron reacts with water at high temperature to yield boric acid and some other by-products. Its reaction with mineral acids may be slow or explosive depending on concentration and temperature, yielding boric acid as the primary product.

Atomic Structure: 

 

 

Atomic Diameter

1.17 Å

 

Atomic Volume

4.6 cm3/mole

 

Crystal Structure

Rhombohedral

 

Electron Configuration

1s2 2s2p1

 

Ionic Diameter

0.23 Å

 

Electron Number (neutral)

5

 

Number of Neutrons

6

 

Number of Protons

5

 

Valance Electrons

2s2p1

 

 

Chemical Properties :

 

 

Electrochemical Equivalent

0.1344 g/amp-hr

 

Electronegative (Pauling)

2.04

 

Heat of Fusion

50.2 kJ/mol

 

Ionization Potential

First: 8.298

Second: 25.154

  Third: 37.93

 

Valance Electron Potential (-eV)

190

 

 

Physical Properties :

 

Atomic Weight:

10.811

Boiling Point:

4275 K - 4002°C - 7236°F

Thermal Expansion Coefficient:

0.0000083 cm/cm/°C (0°C)

Conductivity:

Electrical:  1.0E -12 106/cm

Thermal:  0.274 W/cmK

Density:

2.34 g/cc @ 300K

Appearance:

Yellow-Brown Nonmetallic Crystal

Elastic Modulus

Bulk: 320/GPa

Enthalpy of Atomization

573.2 kJ/mole @ 25°C

Enthalpy of Fusion

22.18 kJ/mole

Enthalpy of Vaporization

480 kJ/mole

Hardness

Mohs:  9.3

Vickers:  49000 MN m-2

Heat of Vaporization

489.7kJ/mol

Melting Point

2573 K - 2300°C - 4172°F

Molar Volume

4.68 cm3/mole

Physical State

(20°C & 1 atm): Solid

Specific Heat

1.02 J/gK

Vapour Pressure

0.348 Pa@2300°C

                 
 
 
 
 
 
 
 
 

© 2018 Her Hakkı Saklıdır. Ulusal Bor Araştırma Enstitüsü