GROUP 13 ELEMENTS 13th GROUP ELEMENTS These elements are placed in 13th (IIIA) group in the long form of periodic table. B Boron H He Li Be B C N O F Ne Al Aluminium Na Mg Al Si P S Cl Ar Ga GalliumK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe In Indium Cs Ba La* Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Tl ThalliumFr Ra Ac** Rf Db Sg Bh Hs Mt Ds Uuu Uub - Uuq - Uuh - - * Lanthanoids Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ** Actinoids Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Electronic configuration of IIIA group elements 1s 2 2s 2 2p 1 5 B = 2 2 6 2 1 13 Al = 1s 2s 2p 3s 3p 2 2 6 2 6 31 Ga = 1s 2s 2p 3s 3p 4s 2 3d 10 4p 1 Electronic configuration of IIIA group elements 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 49 In = 4p 6 5s 2 4d 10 5p 1 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 2 81 Tl = 4s 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 6s 2 6p 1 Atomic Electronic Element No. configuration Their general outer most electronic 2 1 B 5 [He] 2s 2p configuration is ns2 np1 Al 13 [Ne] 3s2 3p1 Ga 31 [Ar] 3d10 4s2 4p1 In 49 [Kr] 4d10 5s2 5p1 Tl 81 [Xe] 4f14 5d10 6s2 6p1 In the penultimate shell, Boron contains 2e–, Aluminium contains 8e–, and other elements contain 18e–. 1) General electronic configuration of IIIA group elements is… a) ns2np2 1 2 b) ns np 2 1 c) ns np d) ns2np3 Abundance of IIIA group elements: Boron is a rare element, mainly it occurs in combined state. It has two isotopic 10 11 forms of B (19%) and B (81%). Boron Important minerals of boron: Borax : Na2 B4 O7 .10H2O Kernite (Razorite) : Na2 B4O7 . 4H2O Orthoboric acid : H3 BO3 Colemanite : Ca2 B6 O11 . 5H2O Abundance of IIIA group elements: ‘Al’ is the most abundant metal and third most abundant element in the earth’s crust. Important minerals : Aluminium Corundum : Al2O3 Diaspore : Al2O3 . H2O Bauxite : Al2O3 . 2H2O Gibbsite : Al2O3 . 3H2O Cryolite : Na3 Al F6 Feldspar : K Al Si3 O8 Abundance of IIIA group elements: Less abundant Ga, In, Tl Highly toxic :: Decreasing Order of Abundance :: Aluminium Gallium Boran Thallium Indium Al > Ga > B > Tl > In % % % % % abundance abundance abundance abundance abundance 0.000005% 8.2% 0.0018% 0.0001% 0.00006% (0.05ppm) (82,000ppm) (18ppm) (10ppm) (0.6ppm) 1) Number of water molecules in Borax… a) 6 b) 8 c) 9 d) 10 2) Formula of corundum is… a) Al2O3.H2O b) Al2O3.2H2O c) Al2O3 d) Al2O3.3H2O 3) Formula of cryolite is a) Na3AlF6 b) 3NaF.AlF3 c) Both a & b d) Na2AlF4 Physical Properties 1) Atomic Mass Atomic mass increases from top to bottom in IIIA group elements B < Al <Ga < In < Tl Physical Properties B Ga Elements Al In Tl 2) Atomic Radius: At. Radii (pm) 88 143 135 167 17 0 B < Ga < Al < In < Tl The sharp increase of atomic radius of ‘Al’ is due to greater screening effect of electrons of penultimate shell. What is screening effect? Decrease in the force attraction of nucleus over the valence shell electrons due to inner core electrons shielding is called screening effect. i.e., greater the screening effect, easier the removal of electron. Physical Properties +3 +3 +3 +3 +3 3) Ionic Radius (M+3) : B < Al < Ga < In < Tl Ionic radius increases from top to bottom in IIIA group. Physical Properties 4) Ionisation Enthalpy : Ionization enthalpy values (decrease) with (increase) in atomic radii. Since, the outer electrons become more loosely held down the group. & so the order of ionization enthalpy: IE1 < IE2 < IE3 …. e– e– + + + IE1 IE2 Atom Monovalent Cation Divalent Cation Physical Properties 4) Ionisation Enthalpy : Ionisation enthalpy from ‘B’ to ‘Al’ but from Al Tl increases marginally. The observed discontinuity in the ionisation enthalpy between ‘Al’ and ‘Ga’ and between ‘In’ and ‘Tl’ are due to lower screening effect of d and f orbitals Elements B Al Ga In Tl I.E. values 801 577 579 558 589 kJ/mol B > Tl > Ga > Al > In ‘B’ has highest I.E. in IIIA group. Physical Properties Elements B Al Ga In Tl 5) Electronegativity : E.N. values 2.0 1.5 1.6 1.7 1.8 The tendency of an atom to attract the Electronegativity decreases from ‘B’ to ‘Al’ shared pair of electrons towards itself is but from ‘Al’ ‘Tl’ increases marginally. known as electro negativity. B > Tl > In > Ga > Al ‘B’ is the most E.N. element in IIIA group. Physical Properties M.pts (K) 6) Melting point : B Al Ga In Tl Boran is extremely hard and black245 933 303 430 576 coloured solid. 3 The M.P. & B.P. of boran are very high. The order of melting point of IIIA group elements is as follows… Due to very strong crystal lattice, boron B > Al > Tl > In > Ga has high melting point. ‘Ga’ has low melting point since it exists as simple Ga2 molecule. Physical Properties 7) Boiling point : The order of boiling point of IIIA group elements is as follows… B.pts (K) B Al Ga In Tl 392 2740 2676 2353 173 3 0 B > Al > Ga > In > Tl Make a Note Due to large difference in temperature (2373K) between m.p and b.p ‘Ga’ is used as a pyro metric liquid. (i.e. filled in high temperature measuring liquid thermometers) Physical Properties 8) Density : Density of the IIIA group elements increases down the group. B Al Ga Elements In Tl Solid state(gm/cc) 2.34 2.69 5.09 7.31 11.5 liquidstate(gm/cc) 2.36 2.37 6.09 7.01 11.2 Physical Properties 9) Electropositive character or Metallic nature : Electropositive character order of IIIA group elements is as given below : B < Al > Ga > In > Tl Or Al >B > Ga > In > Tl 1) Which IIIA group element has lowest melting point? a) B b) Ga c) Al d) Tl 2) The order of electropositive character of IIIA group elements is … a) B > Al > Ga > In > Tl b) B < Al < Ga < In < Tl c) B < Al > Ga > In > Tl d) B < Al < Ga > In > Tl Chemical Properties : 1. Oxidation State : What is inert pair effect? The +1 oxidation state becomes more stable due to inert pair effect. The non-participation of s electron pair in bonding or the reluctance of s electron pair in bonding is called inert pair effect Chemical Properties : 1. Oxidation State : The common oxidation number of group 13 elements is +3. Due to small size of boron, the sum of its first three ionization enthalpies is very high. This prevents it to form +3 oxidation state. Boron exhibits -3 oxidation state with highly electropositive metals Ex: Mg3B2 Chemical Properties : 1. Oxidation State : Along with +3 other elements Ga, In and Tl shows +1 oxidation state The stability of +1 increases from Ga to Tl due to inert pair effect The inert pair effect increases from Ga to Tl EX: TlCl more stable than TlCl3 Chemical Properties : Valency means combining Valency : capacity of an element In general, these are Trivalent compounds as they possess three electrons in their valence shell. In Trivalent state the number of electrons around the central atom will be only 6 in the bonded molecule so, it act as a Lewis acid. Have tendency to accept a pair of electrons to achieve stable electronic configuration. Example : BF3 Chemical Properties : The tendency to behave as a Lewis acid decreases with increase in the atomic size down the group. For example : BCl3 easily accepts a lone pair of electron from ammonia to form H3NBCl3 where as AlCl3 achieves stability by forming a dimer. Cl. .N. .H + .B . H H Cl. Cl (Ammonia) (Boron trichloride) H . Cl . N . B . H . Cl . H Cl Ammonium boron trichloride Nature of compounds of IIIA group elements: IIIA group elements mostly form covalent compounds because of their high ionization energy. Compounds of boron are always covalent but some compounds of other elements like AlCl3, GaCl3 are covalent only in an anhydrous state. Question: Why cannot boron form B+3 ion? Answer: The element with highest sum of ionisation energies I.E1, I.E2 and I.E3 is boron. Hence, it cannot form B+3 ion. Question: Why is the maximum covalency of boran only four whereas that of aluminium is six? Answer: ‘Al’ has vacant ‘d’-orbitals hence it can expand its octet. In boron, there are no d-orbitals at all. Hence, it cannot expand its octet. Question: Write the correct order of reducing nature of group 13 elements in +3 oxidation state. Answer: Reducing nature Al > B > Ga > In > Tl 1) More stable and more common Oxidation state of ‘Tl ‘ is… a) +1 b) +2 c) +3 d) +5 2) AlCl3 exists as… a) Monomer b) Dimer c) trimer d) tetramer 1) Reactivity towards air Boron is unreactive in crystalline form, But in Amorphous form on heating in air forms B2O3 Aluminum will form a very thin oxide layer on the surface of it by heating in the atmosphere of O2 .