GROUP 3 AND 4 ELEMENTS OF PERIODIC TABLE 

GROUP IIIA ELEMENTS

The Group IIIA of the Periodic Table comprises the elements boron, aluminium,Gallium, indium and thallium. Electronic configurations and some physical properties of group IIIA elements.

The small size and high nuclear charge make boron non-metallic while all the other Elements of this group are metals. The abrupt increase in metallic character from B to Al is Associated with the increased size of aluminium atom. The increase in the atomic size is not s group. This is due to the presence of d electrons in heavier members which have Poor shielding effect than s and p-electrons.

Occurrence (Boron and Aluminium)

Boron is not an abundant element. It occurs in traces in most soils and has been found to be essential in very small amounts for the proper growth of many plants. Boron is always found in nature

combined with oxygen, usually as oxyborate ions. Boron occurs principally as salts of various polyboric acids. Aluminium is the third Most abundant element in the Earth’s crust (after oxygen and Silicon).

It occurs primarily as Alumino-silicate minerals found in The rocks of the outer portion of the Earth. The other elements of Group IIIA gallium, indium and Thallium are relatively rare and are Obtained as by-products during the Processing of other metals.

Peculiar Behaviour of Boron

Boron is the first member of the Group IIIA, it shows many dissimilarities with the Members of its own group. The difference in the properties of boron and those of the other Members of the series is mainly due to the large difference in their sizes and ionization energies.

1. Boron is the only element in GroupIIIA which is non-metallic in behaviour.

2. It is the only element with less than four electrons in the outermost shell which is not a metel.

3. Boron always uses all the three of its valence electrons for bonding purposes and its common oxidation states are +3 and-3.

4. One of the outstanding features of the chemistry of boron is its ability to form molecular addition compounds.

5. Boron does not form ionic compounds with sulphate, nitrate or other anions because boron does not from a stable cation.

COMPOUNDS OF BORON

Borax (Sodium Tetraborate Na,B,O,.10H₂O)

Borax is the sodium salt of tetraboric acid. It is the most important of all borates.

occurrence:

Borax occurs as a natural deposit called tincal in the dried uplakes of Tibet and California

Manufacture

1. Formally borax was manufactured by treating a hot solution of boric acid with the proper amount of soda ash.

2. Nowadays borax is almost exclusively obtained from calcium borate. Finely powdered. The clear solution from the top is taken off and is then allowed to crystallize, when crystals of borax separate out. To get more borax, CO₂ is blown through the mother liquor, the sodium metaborate is decomposed into borax, which separates out in the form of fine crystals.

3. Borax may also be obtained from tincal (Na,B,O,.10H₂O) by treating tincal with water and subsequently evaporating the clear solution, when crystals of borax separate out.

Properties:

1. Borax is a white, crystalline solid. It is sparingly soluble in cold water but is more soluble in hot water: 100 grams of water dissolve 3 grams of decahydrate at 10°C and 99.3 grams at 100°C. If a saturated solution be allowed to crystallize above 62°C, octahedral crystals of the pentahydrate, Na,B,O,.5H₂O separate out, if the temperature is below 62°C, the decahydrate is formed. Its aqueous solution is alkaline in nature due to hydrolysis.

2. When heated, borax loses water and swells up into a white porous mass due to the Expulsion of water: on further heating it melts into a clear transparent glass, which Dissolves many metallic oxides forming coloured beads. This reaction forms the basis of borax bead test.

3. When borax is heated with ammonium chloride, boron nitride is produced:

4. Borax when dissolved in water ionizes

5. Hydrolysis of B,O, ions occurs.

So, a strong alkali (NaOH) is formed which is highly ionized. On the other hand, boric Acid (H,BO₂) is ionized to a little extent, because it is a weak acid. Hence, solution of borax as a whole is alkaline in nature.

Borax Bead Test

Prepare a loop at the end of a platinum wire. Heat the wire and take a little powdered Borax on the hot loop. Heat again, borax first swells up and then melts into colourless, glass like Bead on the loop. Now put a few grains of the substance, under examination, on the beads and Re-heat it first in the oxidizing flame and then in the reducing flame.

Chemistry of the Borax-bead Test:

Borax, when fused, is decomposed into sodium metaborate and boric anhydride. The metallic oxide formed from the substance, under examination, combines with B,O, Giving the coloured metallic borates. With cupric oxide, the beads are coloured blue in the Oxidizing flame because cupric borates are blue in colour.

Uses of Borex

1. It is used to prepare borate glass, which is heat resistant.

2. It is used in softening of water.

3. It is employed in borax bead test, for the detection of metallic cations.

4. It is used in metallurgical operations.

5. It is used as a flux in welding and in metallurgy.

6. It is employed in making washing powders.

7. It is used in leather industry for tanning and dyeing.

8. It is used in cosmetics, soaps, textiles, paints, medicine, match industry and as a Preservative.

3.2.2 Boric Acids

There are four important boric acids. Out of these orthoboric acid is the most important And the stable one. The remaining acids are stable in solid state and change into orthoboric acid in Solution.

• Orthoboric Acid, H,BO,

• Metaboric Acid, HBO₂

• Tetraboric Acid, H₂B,O,

• Pyroboric Acid, H.B.0,

Orthoboric Acid or Boric acid (H,BO,)

It is a white crystalline chemical substance (triclinic), sparingly soluble in cold water (2.6% at 40°C) but dissolves readily in hot water (37% at 107°C). This temperature variation in Solubility forms the basis for its separation and purification.

Preparation of Boric acid on Commercial Scale

1.From Colemanite

On commercial scale, boric acid is prepared from a natural calcium borate called Colemanite (Ca,B,O₁₁. 5H₂O) by suspending it in boiling water while, sulphur dioxide is passed Through it. Boric acid crystallizes out from the solution while, the other product CaSO, remains in the solution.

2. From Borax

A hot concentrated solution of borax is treated with a calculated quantity of conc. H₂SO..On cooling, crystals of boric acid formed separate out.