Occurrence of elements in boron family

Boron is found in the form of Orthoboric acid , Borax and Kernite. There are two isotopes of Boron ¹⁰B and ¹¹B. In Boron family Aluminium is the most abundant metal and the third most abundant element on earth. Aluminium is found in the form of Bauxite, Cryolite, and in mineral forms. Gallium, Indium and Thallium are less abundant elements in nature.

Atomic properties of boron family

• Electronic configuration: The general electronic configuration of Boron family is ns² np¹. Boron and Aluminium have noble gas core whereas Gallium and Indium have noble gas core. Moreover, they also contain 10 d electrons in their shell. In same way, Thallium has noble gas core with 10 d electrons as well as 14 f electrons
• Atomic radii: While moving down the group, atomic radius of elements increases. In Boron family, Atomic radius of Ga is less than AI. This is because of variation of inner core of electronic configuration. Gallium have additional 10 d electrons, but they provide poor screening effect and then outer electrons experience higher nuclear charge, thus contracting the atomic radius. Hence, the atomic radius of Gallium (135 pm) is less than Aluminium(143 pm)
• Ionisation enthalpy: The ionisation enthalpy decreases from top to bottom, but, in case of, Boron family, there is an increase and decrease in ionisation energies from Al to Tl. this is because d and f electrons have low screening effect. However, decrease from B to Al is due to increase in size. The observed discontinuity in ionisation enthalpy values between Al and Ga, and In and Tl are due to inability of d and f electrons having low screening effect. However, the order of ionisation enthalpies is
  Δ_i H₁ lessthan Δ_i H₂ lessthan Δ_i H ₃ .
  the sum of first three ionisation enthalpies of each element is high.
• Electronegativity: Electronegativity decreases from B to Al and later increases. Main reason is difference in atomic size of elements.

Physical properties of boron family

Boron has non metallic character. Also, it has allotropes. Boron has high melting point due to extremely strong crystal lattice. However other elements in family are soft metals with low melting point and high electrical conductivity. Melting point of Gallium is 303K , however, boiling point of Gallium is high 2676 K. density of element increases as we move down the group from Boron to Thallium.

Chemical properties of boron family

• Oxidation State: Outer electronic configuration of group 13 elements in ns²np¹. Thus the group oxidation state is +3. Boron and Aluminium shows oxidation state of +3 whereas, other members shows oxidation state of +3 and +1. However +1 is most stable oxidation state.
• Tendency to behave as Lewis Acid : In case of trivalent state there are six electrons around the central atom, however to attain stability there is need of two more electrons. Therefore, the Boron family elements tend to accept a pair of electrons and gain stability. Thus, these elements behaves as lewis acids . The tendency to behave as lewis acids decreases down the group. BCl₃ can easily accept lone pair from NH₃. AlCl₃ achieves stability by forming a dimer.
• Reactivity towards air: At room temperature, Boron does not react with air. At high temperature boron burns in air forming B₂O₃. Aluminium reacts with air and forms thin layer of oxide on its surface. It prevents further oxidation of Al₂O₃. At very high temperature they react with nitrogen forming nitride.
                            Δ
  2E(s) + 3O₂(g) → 2E₂O₃(s)
                          Δ
  2E(s) + N₂(g) → 2EN(s)
  Where E = B, Al, Ga, In, Tl
• Reactivity towards acids and alkalis: Boron remains unreacted in acids and alkalis at low and moderate temperature. However, aluminium reacts with mineral acids and also with aqueous alkalies showing amphoteric nature. Aluminium dissolves in dilute HCl and liberates hydrogen.
  2Al(s) + 6HCl (aq) → 2Al₃⁺(aq) + 6Cl^– (aq) + 3H₂ (g)
  Aluminium also reacts with aqueous alkali and liberates hydrogen gas.
  2Al(s) + 2NaOH(aq)+ 6H₂O(l) → 2 Na⁺ [Al(OH)₄]^–(aq) + 3H₂ (g)
                                                       Sodium tetrahydroxoaluminate(III)



• Reactivity towards halogen: Boron family elements, react with halogens to form trihalides.
  2E(s) + 3 X₂ (g) → 2EX₃ (s)
  Where E = B, Al, Ga, In, Tl and X = F, Cl, Br, I
  Anhydrous aluminium chloride undergo partial hydrolysis with atmospheric moisture and forms HCl gas. It absorb atmospheric moisture and so, moist HCl appears white in colour.
  AlCl₃ +3H₂O → Al(OH)₃ +3HCl(white fume)

Uses of boron and aluminium and their compounds

• Boron is second hardest material. Therefore, Boron fibres are used in making bullet-proof vest and light composite material for aircraft.
• An isotope of boron ¹⁰B have high ability to absorb neutrons, so, metal borides are used in nuclear plants as protective shields and control rods.
• Borax and Boric Acid are used for making glass wool, fiberglass, and heat resistant glasses e.g. pyrex glass.
• Borax is used as a flux for soldering metals, for heat, scratch and stain resistant glazed coating to earthenwares
• Aqueous solution of boric acid act as mild antiseptic.
• Aluminium is bright silvery-white metal having high tensile strength. It has very high electrical conductivity. So it is used for making electric wires.
• Aluminium forms alloys with Cu, Mn, Mg, Si and Zn. These alloys are given the shapes of pipe, tubes, rods, wires, plates and foils. These are used for packing, utensil making, construction, aeroplane and transportation industry.

Keywords: Aluminium, Bauxite, Cryolite,Gallium, Indium, Thallium, Atomic radii, Ionisation enthalpy, Electronegativity, Borax, Orthoboric acid, Lewis Acid

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