Boron (B), atomic number 5, is the first chemical element of Group 13 or Group IIIA in the periodic table has the smallest size and highest electronegativity, the compounds are essential to plant growth and wide industrial application of ancient civilization.

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Boron
Boron in Periodic Table
Boron (B), atomic number 5, is the first chemical element of Group 13 or Group IIIA
in the periodic table has the smallest size and highest electronegativity, the
compounds are essential to plant growth and wide industrial application of ancient
civilization. The small size, high ionization energy, and moderate electronegativity
(close to carbon and hydrogen) explain the formation of many exciting and unusual
covalent bond or compound of boron in chemistry. The natural boron contains two
isotopes like B or B-10 (19.6 percent) and B or B-11 (80.4 percent). Boron in the
Group 13 of the periodic table member occurs in a small amount due to its nucleus
being disintegrated by natural bombardment reactions but aluminum is very
abundant, occupies the third position after oxygen and silicon.
Properties and Occurrence
10 11

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Pure boron is a high melting solid diamagnetic substance (melting point = 2180 °C)
which be either crystalline (black) or amorphous (brown), uses as a semiconductor
conducts electricity at high temperature like a metal. Crystalline boron exists in
several allotropic forms which are structurally very complex, build up by B
icosahedra. Different types of packing on icosahedra in-unit crystal lattice form
different types of the structural formula of boron, the simplest form is α-
rhombohedral.
12

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The abundance of boron in crustal rocks (9 ppm) of our earth universe is very low
which is less than that of lithium (18 ppm) or lead (13.1 ppm). The vast deposits of
boron minerals like borate or borosilicates are occurred in the regions of California,
Turkey, Russia, and Argentina by former volcanic activities and water from hot
springs. The principal minerals of boron are colemanite, Ca [B O (OH) ] , 2H O;
kernite Na [B O (OH) ], 2H O; and borax, Na [B O (OH) ], 8H O. In India, Tibet,
and Sri Lanka, borax occurs as a precipitate from hot springs.
History, Isolation, and Uses
In history, the different civilizations of the world, the compound of boron borax uses
as a flux, or prepared glazes and hard glass. The element itself was isolated in the
nineteenth century by Davy, Gay Lussac, and Thenard by electrolysis of moist boric
acid. Moissan in 1892 prepared a rather pure specimen of boron (95 percent) by
heating B O with magnesium metal and the name proposed by Devay to illustrate its
source and similarities to carbon. The crystalline form of high purity element is now
obtained by reduction of volatile boron compounds (BCl or better BBr ) with
2 3 4 3 2 2
2 4 5 4 2 2 4 5 4 2
2 3
3 3

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hydrogen on heated titanium wire. However, the process can operate to form the
element on a kilogram scale. Below 1000 °C, amorphous boron is obtained, between
1000 to 1200 °C α and β-rhombohedral form is obtained and above 1200 °C
tetragonal crystal is formed.
In large quantities, the amorphous boron is obtained by reduction of B O with
magnesium (Mg) or other electropositive metals at high temperatures (B O + 3Mg
→ 2B + 3MgO). The reaction is exothermic with the free energy at 298K = -515 kJ.
The unreacted substances and MgO can be removed by washing the substance with
dilute hydrochloric acid (HCl) and sodium hydroxide (NaOH) solutions. The 95
percent pure boron powdered is cheaply obtained by electrolytic reduction of KBF in
molten KCl or KF at 800 °C.
Boron and its compounds are extensively used in filaments and fiber composites used
in reinforcement materials (space shuttles and aircraft). Boron carbides are used as
abrasive for polishing or grinding, the carbides and metal borides are extensively used
in neutron shielding and control rods for nuclear power plants. The isotope of boron
( B) has a high absorption cross-section for high energy neutrons (10 to 10 eV) is a
more beneficial substance in B-10 neutron capture therapy of brain tumors. Metal
borides (TiB , ZrB ) have found much technical application. Due to the physical and
chemical properties like high melting point, hard nature, and chemically inertness of
metal borides (compound of boron), metal borides are used as a coating on turbine
blades, rocket nozzles, and high-temperature reaction vessels. Boric acid, B O , and
borax are used in medicine, in making borosilicate glass, enamels, and fire retardant.
Chemical Reactivity of Boron
The crystalline elemental form of boron is chemically very inert and not affected by
acids or oxidizing agents but fused sodium hydroxide (NaOH) at 500 °C attacks to
form NaBO and hydrogen gas. The amorphous form is more reactive than the
crystalline form. Therefore, the amorphous elements of Group 13 (B, Al, Ga, In) burns
2 3
2 3
4
10 4 6
2 2
2 3
2

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in the air to form trioxides and nitrides. It dissolves in oxidizing acid-like nitric acid
(HNO ) or sulfuric acid (H SO ) but unreacted with hydrochloric acid (HCl). Only
boron and aluminum combine directly with nitrogen when heated to form BN and
AlN but GaN and InN may be obtained indirectly by heating the metals with
ammonia.
Boron Compounds
The electron configuration of boron is 1s 2s 2p , with the two electrons in s-orbitals
and one electron in p-orbital suggest the monovalent state but it never exhibits +1
oxidation number, only shows +3 state of the chemical element. The chemistry of the
first member of the boron family is naturally influenced by the small size and high
ionization energy and the compounds will be essentially covalent chemical bonding
with the oxidation state III. The formation of B ion appears unlikely for two main
reasons, the ionization energy for the formation of B ion would be very large, and
small ion has highly polarizing properties. Due to the presence of three bond pairs,
the compounds of boron function as a Lewis acid by accepting electron pairs from the
Lewis base.
The electron deficiency defines the unique characteristics of boron to form Pi-bonds
with elements like chlorine, fluorine, etc. In BH , BCl or BF , the element attains
noble gas configuration through dimerization of the molecule. Due to its small size,
the boron atom can readily form a stable lattice with metal atoms (interstitial alloy),
chain species, and three-dimension networks. Depending upon the individual
structure and chemical reactivity, the principal boron compounds may be classified
into, hydrides and their derivatives (carboranes and polyhedral borane metal
complexes), halides, oxygen compounds including polyborates, borosilicates, metal
borides, nitrogen, and organoboron compounds in learning chemistry.
3 2 4
2 2 1
+3
+3
3 3, 3