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Boron Family

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Boron family of elements contains five elements namely boron, aluminum, gallium, indium and thallium. Except boron which is classified as a non metal all other elements of this group are metals. The general electronic configuration of these elements is ns2np1. These elements belong to p block of the periodic table.

The p-block is the most typical amongst all the blocks of the periodic table. It consist of nonmetals, metals and metalloids which exist under normal temperature conditions in all three states of matter, solid or liquid or gas.

Boron Family Elements

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The elements given below belong to Group 13 of long form of periodic table. These are also called elements of boron family. Out of all these elements Boron is a non metal while all others are metals.

Boron
Aluminum
Gallium
Indium
Thallium
5B11 13Al17 31Ga70 49In118 81Th168

These elements do not occur free in nature, rather they are generally found as oxides in many locations around the earth.

Boron Family Name

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The electronic configuration of the boron family is ns2np1. The element of this group are boron, aluminum, gallium, indium and thallium. On moving down the group following characteristic are seen.
  1. Increase in atomic size
  2. Increase in density
  3. Increase in ionic character
  4. Decrease in polarity

Among all the members of this family boron is a nonmetal while the rest are metals whose metallic characteristic increases down the group. The non metallic character of boron is due to its small size and high ionization energy.

Atomic Weight of Boron

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The atomic weight of an element is the average mass of a representative sample of atoms of the element expressed in atomic mass units. Atomic mass of boron family elements are given below.

S.No
Element
Atomic weight (amu)
1 Boron 10.811
2
Aluminum
26.98
3
Gallium
69.72
4
Indium
114.81
5
Thallium
204.38

In general the atomic weight of an element is found from the percent abundance. The mass of each isotope is multiplied by its fractional abundance, the percent abundance expressed as a decimal to calculate the weighted average the atomic weight.

Atomic weight = (fractional abundance $\times$ isotopic mass) of isotope 1 + (fractional abundance $\times$ isotopic mass) of isotope 2 + ......(fractional abundance $\times$ isotopic mass) of isotope n

Boron Compounds

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Boron combines with other elements to form compounds and alloys. Compounds always form in fixed proportions so that boron oxide always pairs two boron atoms with three oxygen atoms.

The compounds that boron forms are held together by covalent bonds. In covalent bonding valence electrons are shared between atoms. The attraction of each atom on the shared electrons is what binds the atoms together.

Fluoroboric Acid


Fluoroboric acid may be prepared by adding hydrochloric acid to sodium fluoroborate or by dissolving boric acid in 50 percent hydrofluoric acid, the latter usually gives better yields. H3BO3 dissolves in aqueous HF to give fluoroboric acid according to the reaction.

H3BO3 + 4HF $\rightarrow$ H+[BF4]- + 3H2O

Fluoroboric acid is a strong acid and [BF4-] ion is tetrahedral.

Borazine


Borazine B3N3H6 is of special interest because it is iso-electric with benzene and some of its physical properties show some striking similarities with benzene. Borazine is prepared by heating a mixture of lithium borohydride and ammonium chloride in vacuum at 230oC.

3NH4Cl + 3LiBH4 $\overset{230^{o}C}{\rightarrow}$ B3N3H6 + 3LiCl + 9H2

This is the laboratory method for preparation of borazine. It is a colorless liquid having boiling point 64.5oC. The structure of borazine is given below.

Borazine

Boric Acid

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The trival name for boric acid is orthoboric acid. It has a layer type structure in which BO3 units are linked through H atoms. H atoms form covalent bond with one unit whereas H-bond with the other.

By acidifying an aqueous solution of borax with hydrochloric acid or sulfuric acid boric acid is prepared.

Na2B4O7 + 2HCl + 5H2O $\rightarrow$ 2NaCl + 4H3BO3

Boric Acid Uses


Boric acid is used in
  1. The manufacture of enamels and glazes for pottery.
  2. Making heat resisting and shock resisting glass.
  3. Washing eyes.

Boron Nitride

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The majority of precursors for boron nitride preparation are based on boraxene, substituted borazene and their polymeric forms. The pyrolysis of borazene and its monomeric derivatives proceeds with condensation through BN - analogues of naphthalene and biphenyl derivatives and with further cross linking up to boron nitride.

It is prepared by the action of nitrogen or ammonia on boron at 1000oC

2B + N2 $\rightarrow$ 2BN

Boron nitride has a layered lattice structure. Each layer consist of hexagonal arrangement of boron and nitrogen atoms. The structure is similar to that of graphite. The structure of boron nitride is given below.

Boron Nitride

Boron Family Periodic Table

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Group 13 of long form of periodic table includes boron (B), aluminum (Al), gallium (Ga), indium (In) and thallium (Tl). Boron is the first member of group 13 of the periodic table and is the only non metal of this group. The all other members are metals. The non metallic nature of boron is due to its small size and high ionization energy.

Boron Family Periodic Table

The members of this family are collectively known as boron family and some times as aluminum family.

Boron Family 3 Valence Electrons


Boron is a non metal, whereas other elements show metallic properties. As these elements have three electrons in their valence shell so they can show +3 oxidation state. Boron does not lose all the valence electrons to form B3+ ion. Ga, In and Tl show +1 and +3 oxidation states and +1 state becomes more prominent as we move down the group. it is due to inert pair effect.

Boron Family Facts

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  1. Homburg in 1702 first isolated Boron by distilling borax with green vitriol.
  2. Boron exist in amorphous and crystalline allotropic forms. The amorphous form is reactive while crystalline form is inert.
  3. Boron never forms cation and coverts to anion only.
  4. Boron salicylic acid is an optically active compound.
  5. Boron is used in making light composite materials for the aircraft.
  6. Boron is a semiconductor and used in electronic devices.

Boron Family Properties

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What are the Properties of Boron?

As we move down the group atomic weight, atomic volume, atomic and ionic radii and density show an upward increases. There is a decrease in hardness boiling points and heats of sublimation as we move down the group. Melting point decreases as we move down from B to Ga then increases for In to Th.

The boron family characteristics are discussed below in physical and chemical properties of boron family.

Physical Properties of Boron


  1. Electronic configuration configuration -There are three electrons in the outer most orbit of each element of this group and that is why their orbit general electronic configuration is ns2np1.
  2. Atomic and ionic radii -Atomic and ionic radii and atomic volume increase from top to bottom in the group.
  3. Density -In general on moving down the group the density decreases from B to Tl because increase in size of the atom.
  4. Melting and boiling point -Melting point do not show a regular trend. Boron has high melting point and it decrease from B to Ga and then increases.
  5. Oxidation state -A common oxidation state of all these elements is +3 and they exist as M3+ ions.
  6. Ionization energy and electropositive nature -The ionization energy values of these elements are low as compared to s-block elements of comparable atomic number. These elements are electropositive in nature but less compared to s-block elements. Down the group electropositive character increases.
  7. Hydration of ions - Only ions of metallic elements get hydrated with six molecules of water and form as octahedral structure.

Chemical Properties of Boron

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The chemical properties of boron compounds are listed below.

Oxides and hydroxides -All the elementsof group 13 form oxides of the formula M2O3. Hydroxides [M(OH)3] of these elements also follow the same trend.

Hydrides -Boron forms a large number of covalent hydride called Boranes like B2H6, B2H8 etc.

Halides -They also form halides of the type MX3. Due to its small size ad high electronegativity B forms most stable halides.

Action of water-Amongst all these elements only B reacts with water and form ortho-boric acid.
2B + 6H2O $\rightarrow$ 2H3BO3 + 3H2

Action of alkalies -Boron dissolve only in fused alkali, while Al and Ga dissolve in fused as well as aqueous alkalies liberating H2. In and Tl are not attacked by alkalies.

2B + 6NaOH $\rightarrow$ 2Na3BO3 + 3H2
2Al + 2NaOH + 2H2O $\rightarrow$ 2NaAlO2 + 3H2


Action of acids -Boron is not attacked by non oxidizing acids while other elements dissolve in acids forming their respective salts. The oxidizing acids react with all these elements.

2B + 3H2SO4 $\rightarrow$ 2H3BO3 + 3SO2
2Al + 6H2SO4 $\rightarrow$ Al2(SO4)3 + 3SO2 + 6H2O

Boron Family Uses

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Boron is used
  1. As a catalyst for polymerization process
  2. As a reducing agent in organic reactions
  3. For welding torches
  4. In high energy fuels and propellants an their combustion leads to a strongly exothermic reaction.
  5. Boric acid is used as preservative in making potteries, earthen pots and glasses.
  6. In dying leather and as cleansing and stiffening agent in laundry.
  7. It is used in borax bead test.
  8. As a flux in soldering welding and metallurgical processes.