The p-Block and Group 13 Elements

• The p-block elements are located in groups 13 to 18 of the periodic table.
• They are characterized by having their valence electron(s) in the p-orbital.
• This group includes metals, metalloids, and non-metals.
• The general electronic configuration is ns² np¹⁻⁶ (except for He which is 1s²) where n is the outermost shell.
• The p-block includes the Boron, Carbon, Nitrogen, Oxygen, Halogens and Noble Gas groups

Boron Group (Group 13)

• The group 13 elements are Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl).
• Boron is a metalloid while the rest of the elements are metals.
• Their general electronic configuration is ns² np¹.
• They exhibit a +3 oxidation state, with heavier elements also showing a +1 oxidation state due to the inert pair effect.
• The inert pair effect refers to the tendency of the two s electrons in the outermost shell to remain un-ionized or unshared in compounds.
• Boron differs significantly from the rest of the group due to its small size and high electronegativity.

Occurrence

• Boron occurs as orthoboric acid (H₃BO₃), borax (Na₂B₄O₇.10H₂O), and kernite (Na₂B₄O₇.4H₂O).
• Aluminium is the most abundant metal and the third most abundant element in the earth's crust.
• Gallium, indium, and thallium are less common.

Physical Properties

• Boron is a hard, black solid with a high melting point and exists in many allotropic forms.
• Aluminum is a silvery-white, lustrous metal.
• Gallium has an unusually low melting point (302.70 K), so it can exist in a liquid state during summer.
• Their metallic character increases down the group from Boron to Thallium.
• Their atomic radii increase down the group, but there is a slight discrepancy between Al and Ga due to lanthanide contraction.
• Ionization enthalpy decreases down the group.
• Electronegativity decreases down the group.

Chemical Properties

• The group 13 elements show a +3 oxidation state.
• Heavier elements, such as Tl can also exhibit a +1 oxidation state.
• The stability of the +1 oxidation state increases down the group (inert pair effect): Al < Ga < In < Tl.
• Boron compounds are electron deficient, and act as Lewis acids.
• They react with oxygen to form oxides of the type E₂O₃.
• They react with nitrogen to form nitrides of the type EN.
• They react with halogens to form trihalides (EX₃).
• Reactivity towards acids and alkalies: Aluminum dissolves in mineral acids and aqueous alkalies and thus shows amphoteric character.

Important Compounds of Boron

• Borax (Na₂B₄O₇.10H₂O) is an important boron compound.
• It is a white crystalline solid and is soluble in water.
• Boric acid (H₃BO₃) is a weak monobasic acid and is prepared by acidifying borax solution.
• Diborane (B₂H₆) is an important hydride of boron.
• It is a colorless, highly toxic gas and catches fire spontaneously in air.
• Boron trifluoride (BF₃) is a Lewis acid that forms adducts with ammonia.

Uses of Boron and its Compounds

• Boron is used in the production of hard steel.
• Boron fibers are used in making bullet-proof vests and light composite materials for aircraft.
• Borax is used in the manufacture of heat-resistant glass.
• Boric acid is used as an antiseptic and eye wash.
• Diborane is used as a reducing agent in organic synthesis.
• BF₃ is used as a catalyst in many industrial processes.

Important Compounds of Aluminium

• Aluminum oxide (Al₂O₃) is amphoteric in nature, i.e., it reacts with both acids and bases.
• Aluminum chloride (AlCl₃) is a Lewis acid and is used as a catalyst in Friedel-Crafts reactions.

Uses of Aluminium and its Compounds

• Aluminium is used extensively in the packaging industry.
• It is used for making aircraft and transportation equipment.
• Aluminium foil is used for packaging food.
• Aluminium compounds are used as catalysts and adsorbents.