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PNC IIA group 2023.pptx

  2. GROUP 13 ELEMENTS-THE BORON FAMILY ELEMENT SYMBOL ELECTR. CONF. Boron B [He]2s22p1 Aluminium Al [Ne]3s23p1 Gallium Ga Ar]3d104s2 4p1 Indium In [Kr]4d105s2 5p1 Thallium 2 Tl [Xe]4f145d106s2 6p1
  3. 3 INTRODUCTION ➢Boron is the only group 13 element that is a non-metal. ▪ The remaining members of this group are fairly reactive metals, and are called p-block elements. ▪ Aluminium, Al, is the third most abundant element in the Earth's crust ▪ All elements show a stable oxidation state of +3, except for thallium. 3
  4. 4 ▪ The small sizes of the ions, their high charge and large values for their sum of the 1st ionization energy suggest that the elements are largely covalent. ▪ Boron is always covalent and many simple compounds like AlCl3 and GaCl3 are covalent when anhydrous. ▪ However, in solution, the large amount of hydration energy evolved offsets the high I.E and hence all ions exists in hydrated states.
  5. 5 ▪ Unlike the s-block elements, some of the elements of this group display lower valency. ▪ There is an increase in tendency to form univalent compounds as you go down the group, and univalent thallium compounds are the most stable. ▪ This monovalency is occurs because s-electrons in the outer shell remaining paired, and therefore not participating in bond formation……because the energy to unpair them is too great.
  6. 6 ▪ This tendency occurs among heavy elements in the p-block and is called the INERT PAIR EFFECT. ▪ Inert Pair Effect is the resistance or reluctance of s-electrons to get unpaired, or take part in covalent bonding. ▪ It is only p orbital electrons, which are involved in bond formation. 6
  7. 7 ▪ Group 13 metals have silver luster. ▪ Erratic variation in M.P is observed down the group. B(2300 ºC), Al(660.4 ºC), Ga(29.78 ºC), In(152.6 ºC) and Tl(303 ºC) • • Low M.P of Ga is reflected in the unusual structure of the metal, which contains Ga2. The general trend down Group from non-metallic to metallic character. – Boron has a covalent network structure. – Other elements are more ionic and metallic in character.
  8. 8 – Aluminium is on the borderline between ionic and covalent character in its compounds. – The remainder of Group 13 elements are generally considered to be metals, although some compounds exhibit covalent characteristics. ❑Electropositive character /nature of the element in this group increases from Boron to Aluminium and then decreases from Aluminium to Thallium (why?) 8
  9. 9 value. ▪ REASON ▪ This increase of electropositivitity from Boron to Aluminium is associated with increasing size. ▪ However, B and Al follows immediately after s block elements, while Ga, In and Tl follows after d block elements. ▪ So the extra d-electrons in Ga, In and Tl do not shield the nuclear very effectively, as a result their orbital electrons are more tightly held and the metal are less electropositive. ▪ Evidenced by the increase of IE between Al and Ga even though the large atom would be expected to have a9lower
  10. 10 OCCURRENCE AND EXTRACTION ➢ Group 13 elements are not found free in nature, but are all present in various minerals and ores. ▪ Aluminiun is the most abundant metal in the Earth's crust making up 8% existing in igneous rocks. – Feldspars -(KAlSi3 O8 , NaAlSi3 O8and CaAl2 Si2 O8). – Micas -given by general formula X2Y4-6Z8O20(OH, F)4 where X = K, Na or Ca; Y = Al, Mg, Fe and Z = Si) – Clays – occurs naturally, show plasticity through a variable range of water content e.g. Kaolinite, Al2Si2O5(OH) and Pyrophyllite, Al2Si4O10(OH)2 . – Cryolite (Na3AlF6 – sodium aluminium fluoride)
  11. 11 – Spinel (MgAl2O4) – Bauxite (Al2O3..H2O) – Gemstone, which are impure form of the oxide of Al2O3 containing small amount of transition metals that give them colours. E.g. ✓ Ruby: Al2O3 + traces of Cr3+ ✓ Blue Sapphire: Al2O3 + traces of Fe2+, Fe3+ and Ti+4 ✓White Sapphire: The germ from aluminium itself 11
  13. 13 EXTRACTION OF ALUMINIUM ❑ Chief ore : Bauxite (Al2O3..nH2O) ❑ Impurities: Silica, Iron(III) Oxide,calcium Oxide And Titanium Hydroxide, and other few oxides ❑ Additive: cryolite (Na3AlF6). -Bauxite is dissolved in molten cryolite, Na3 AlF6 (Sodium hexafluoroalumiminate) so as to lower its M.P ❑ Method: Electrolytic reduction -Since Aluminium is reactive it is not extracted by chemical reduction e.g. C …… bauxite forms carbide. -Usually produced by the electrolysis of bauxite. ❑ Electrolytic process: achieved by the Bayer – Hall Herout processes (… major industrial process for production of Al)
  14. 14 14
  15. 15 Step 1:Digestion ▪ Ground metallurgical-grade bauxite is digested in caustic soda solution at 140 – 280°C in pressure tanks. ▪ Red mud is filtered off: Al2O3 . 3H2O + 2NaOH →Na2O.Al2O3 + 4H2O + red mud bauxite caustic soda Sodium Aluminate filtered ▪ NOTE: Except Alumina And Silica all other impurities (calcium oxide, iron oxide, titanium oxide) DO NOT dissolve in the caustic soda liquor. ▪ The aluminate solution is filtered leaving behind the impurities. ▪ Silica dissolved in the liquor is then precipitated from it by slow heating. 15
  16. 16 Step 2: Precipitation ▪ Caustic soda is added to precipitate pure Al(OH)3 from Sodium Aluminate solution by seeding. Na2O.Al2O3 + 3NaOH→2Al(OH)3.nH2O(s) +liquor ▪ Seeding of aluminum hydroxide reverses the reaction 16
  17. 17 Step 3: Calcination ▪ "Hydrate", is calcined to form alumina . ▪ In the calcination process water is driven off to form alumina, this takes place at 1050oC: 2Al(OH)3.3H2O(s) →Al2O3 + nH2O ▪ The calcination process must be carefully controlled since it dictates the properties of the final product. ▪ A large amount of the alumina so produced is 17 then subsequently smelted
  18. 18 Step 4 : Smelting (Electrolytic Reduction) ➢ Pure Al2O3 is dissolved in a molten Cryolite, Na3AlF6, in an electrochemical cell. ▪ ▪ Molten Cryolite lowers the M.P from above 2000°C to 950– 1000°C). to save energy operational cost. At the cathode, ▪ - Al2O3 is reduced to molten Al. At the anode -Oxygen from the alumina reacts with the C electrode to form CO2(g). NB:The overall cell reaction is written as: 18 2Al2O3 (l) + 3C  4Al (l) + 3CO2 (g)
  20. 20
  21. 21 Uses Of Aluminum Use Transport Construction Examples Superstructures of trains, ships and airplanes. Alloy engines for cars. Window frames, doors roofing Overhead electricity cables, capacitor foil Kettles, saucepans Power transmission Kitchen utensils Packaging Drink cans, foil wrapping Chemical industry Al(OH)3 – flame retarder, paper making 2 4 3 Al (SO ) – flocculant in sweage treatment and to precipitate PO43- Al2O3 – catalyst and catalytic support material, abrasive
  22. ENVIRONMENTAL IMPACT ▪ Smelting processes of aluminum requires enormous amount of electricity. ▪ Also, the main process which is the electrolysis emits carbon dioxide which is greenhouse gas. ▪ Recycling aluminum is an important method of saving energy and minimizing the environmental damage. ▪ Recycling aluminum requires only 5% of the energy 22
  24. 24 ➢Boron is found in ores widely distributed in Earth's crust. ▪ Chief ore: BORAX……..the hydrated borates, Na2B4O7.10H2O and similarly for tri, tetra and pentaborates of calcium and sodium. ▪ Additive: Na or Mg to as reducing agents …..reduces the oxides (B2O3) OR using H2 in the presence of BCl3 and Tungsten (W) filament 24
  25. 25 ❖Extraction/Preparation of some boron compound from Borax 25
  26. 26 ❑GALLIUM, INDIUM AND THALLIUM and miner ➢The elements Gallium, Indium Thallium are only found as components of various minerals. ▪ These elements are produced or extracted by electrolytic reduction in aqueous solution ▪ They are relatively soft and which readily dissolve in acids. reactive, 26
  28. Property Atomic number (Z) B 5 Al 13 Ga 31 In 49 Tl 81 Outer electron configuration 2s22p1 3s23p1 4s23d104p1 5s24d105p1 6s24f145d106p1 Atomic rradii (pm) 80-90 143 122 167 170 Ionic radii (pm) 20 54 62 80 89 Electronegativity 2.37 1.50 1.60 1.70 1.80 Melting point (°C) 2300 660 29.7 156 304 Boiling point (°C) 3650 2467 2403 2080 1357 Density (g/cm3) 2.37 2.696 1.607 7.310 1.80 Ionization energies - 1st Ionization energies - 2nd Ionization energies - 3rd M(s)  M3+(aq) + 3e- Standard Reduction Potentials (V, at 25°C) M2+(aq) + 2 e-  M(s) 28 800.6 577.6 578.8 558 589.3 2427 1816 1979 1820 1970 3659 2744 2962 2704 2877 -0.87 -1.66 -0.53 -0.34 -0.72 Hardness - 2.75 1.5 1.2 1.25 Electroconductivity 59.7 9.1 19.0 82.882
  29. 29 ▪ The M.P of all the elements are high, - but the melting point of boron is much higher than that of beryllium in Group 2 - M.P of aluminium is similar to that of magnesium in Group 2 (diagonal relationship). ▪ The densities of all the Group 13 elements are higher than those of Group 2 elements. 29
  31. 31 ➢The chemical properties of Group 13 elements reflect the increasingly metallic character down the group. -Here only boron and aluminium will be considered. ▪Boron is chemically unreactive except at high temperatures. ▪Finely divided boron burns in air to form oxide and nitride: 4B(s) + 3O2(air) ® 2B2O3 (Oxide) 2B(s) + N2(air) ® 2BN (Nitride). ▪ Accordingly in halogen Boron form trihalides 2B(s) + 2X3(g) ® 2BX3. 31
  32. 32 ❑GROUP 13 COMPOUNDS ▪ Because of their electron-deficient nature, M3+compounds have a formally vacant npz orbital and usually act as Lewis acids (electron acceptors). 32
  33. 33 OXIDES (M2O3) -SESQUIOXIDE ▪ SESQUIOXIDE is an oxide containing three atoms of oxygen with two atoms (or radicals) of another element. ▪ The M2 O3of all the elements can be made by heating the elements in oxygen: 4M (s) + 3O2(g) → 2M2O3 (s) ▪ But B2O3 is more usually made 33 by
  34. 34 34 B(OH)3 +H2O 100 oC -H2O +H2O Red hot -H2O HBO2 Metaboric acid, which exists in three crystalline forms of which contains the cyclic unit B2O3 Boron oxide Orthoboric acid O O B O B OH OH H OH B H
  35. 35 ▪ H3BO3 is a weak acid……due to its electron deficient tendency. ▪ The B(OH)3 accepts an OH- ion from the self ionization of water forming a complex ion. ▪ by the B(OH)3 + 2H2O → [B(OH)4]- + H3O+ The hydroxide boric acid B(OH)3 is formed hydrolysis of many boron compounds. ▪ It has a layer structure made up of planar molecules linked by hydrogen bonding (ref slide overleaf). ▪ It is a Lewis acid that acts as a Brønsted acid . 35
  36. 36 36 Oxidesofoxidationstate+3oftheGroup13Elements O x i d e P r o p e r t y B 2 O 3 ● Weakacid ● manymetaloxidesgivesglasses withB2O3 asintheboraxbeadtest Al2O3 andGa2O3 ● A m p h o t e r i c In2OandTl2O3 ● Weakbasic ● Tl2O3givesO2 andTl2Oonheating to100°C
  37. 37 HALIDES OF GROUP 13 ELEMENTS BCl3 + H2O ¾→H3BO3 + 3HCl ▪ All elements form trihalides. ▪ They are nonpolar with trigonal planar shape. ▪The halides of boron are BX3 are all volatile, highly reactive, covalently bonded molecular compounds and are gases ▪The Boron fluoride (BF3) form fluoroborates, WHILE other Boron halides giving boric acids BF3 + H2O → [BF3OH] H 37
  38. 38 ▪ BX3 are Lewis acids and the order of their Lewis acidity strength is: BF3 < BCl3 < BBr3 to the order of of the attached ▪ In contrary Electronegativity halogens: F > Cl > Br 38
  39. 39 ▪ BX3 are trigonal planar and monomeric (not dimerized in the way the BH3 does.) E.g. the structure of BBr3. 39
  40. 40 electrons in its outer shell and can readily accept a ➢BF3 is a useful organic catalyst for Friedel Craft reaction such as: ✓ Alkylations ✓ Acylation ✓ Estirification ✓ Polymerization of olefines ▪ REASON: -Boron (an electron deficient atom) in BX3 has 6 40
  41. 41 ▪ The fluorides of: Al, Ga, In, and Tl are ionic having high melting points. ▪ The other halides of these metals are covalent when anhydrous. ▪ AlCl3 , AlBr3 and GaCl3 exist as dimers thus attaining an octet of electrons 41
  42. 42 ▪ Exist as dimeric molecules with the formula M2X6 using two atoms to bridge the halide metals. ▪ This retained dimeric formula is when the halides dissolves in non-polar solvent (e.g.; Benzene). ▪But because of high heat of hydration when halides dissolves in water, the covalent dimer is broken into [M.6H2O42] Figure. 1
  43. 43 ▪ Aluminium chloride, AlCl3, is a volatile solid which sublimes at 458K. ▪ The vapour formed on sublimation consists of an equilibrium mixture of monomers (AlCl3) and dimers (Al2Cl6). ▪ It is used to prepare the powerful and versatile reducing agent lithium43
  44. 44 AlCl3 + Lewis Acid C2H5 – O – C2H5 dimethyl ether ( Lewis base ) 44 ▪ AlX3 (Aluminium halides) are very reactive lewis acids – they accepts a pair of electrons forming an acid base compound called adducts
  45. 45 ▪ AlX3 is used as a catalyst in a number of organic reactions. E.G. When benzene is treated with acyl halide in the presence of anhydrous Alcl3 as catalyst ¾® aromatic ketone 45
  46. 46 ▪ The B-X bond distances are shorter than might be expected, and the B-X bond energies are correspondingly higher. E.g. B-F bond energy (646 KJmol-1) is the highest known for a single bond. ▪ EXPLANATION: This suggest that some π-bonding may be existing between the unhybridized 2p orbital of the boron and the filled np orbitals of the halides. 46
  47. 47 HYDROXIDES ▪ Al(OH)3 is amphoteric and reacts with acids in a manner as metal hydroxides do. Al(OH)3 (s) + 3H3 O+ → [ Al( H2 O )6 ]3 +(aq) ▪ Al(OH)3 also reacts with a base in the reaction represented as the formation of a hydro-complex Al(OH)3 (s) + OH-  [ Al( OH )4 ]-(aq4 )7
  48. 48 ▪ When Al(OH)3 dissolves in a base, hydroxyl ion and water bonds to Al ion forming a complex ion [ Al( H2 O )2 (OH)4]-. ▪ The reaction is as follows Al(OH)3 (s) + OH-(aq) + 2H2 O(l) → [Al(H2 O )2 (OH)4]- ▪ Al(OH)3 is used in the purification of water because it carries down any suspended materi4a8l in the water including most of the bacteria.
  49. 49 HYDRIDES ▪ Special compounds that start of predominantly covalent and become more ionic as we go down the group. ▪ Most of the group 13 elements react directly with hydrogen, and large number of interesting hydrides are known. ▪ Boron forms an extensive and interesting series of hydrides, called BORANES. ▪ The simplest of these is not BH3as expected, but its 49 dimer B H .
  50. 50 ▪ The 8 well characterized boranes which fall into two series BnHn+4 and less stable series BnHn+6 are: Diborane Tetraborane Pentaborane (stable) Pentaborane (unstable) Hexaborane i. B2H6 ii. B4H10 iii.B5H9 iv.B5 H1 1 v. B6H110 vi.B9H15 Nonaborane (enneaborane) vii.B10H14 decaborane 50
  51. Cont……. ▪ The borane molecule (BH3) may exists as a reaction intermediate. ▪ But no BH3as it does not exist as separate molecules. Boranes are highly unstable due to their extreme electron deficiency. ▪ Their highly exothermic reaction with oxygen lead to their consideration as rocket fuels by the space program ▪51 The simplest boron hydride that have been isolated is ▪ The B-atom in BH3 lacks the complete octet (i.e. it has only 6 electrons in the valence shell). 51
  52. 52 THE STRUCTURE OF B2H6 (DIBORANE) – MULTICENTRE BONDS ▪The question of interest is what holds the diborane together? EXPLANATION OF THE STRUCTURE OF B2H6. ▪There are 12 valence electrons at for chemical bonding (B has 3, and H has 1, so 2  B + 6  H = 12) •Each terminal B-H bond has two electron bond, and there are fou5 r 2 of then, thus accounting for a total of 8
  53. 53 ▪ This leaves a total of four electrons to be shared between the two bridging H atoms and the two B-atoms. ▪ For this reason, two bridging bonds are B  H  B formed, each consisting two electrons forming the so called three centre – two electron bond (3C, 2e). ▪ Meaning that 3 atoms share 2 electrons (This sometimes called banana bonds because they non-linear but curved. (Fig. below ) 53
  54. 54 Figure 4. The Structure of B2H6 (diborane) – multicentre bonds. 54 Contains a 3-centre-2-electron bond (called a banana bond)
  55. 55 INDUSTRIAL INFORMATION / APPLICATION ➢Boron is used in: ✓ flares to provide a highly visible green colour. ✓Boron filaments are now used extensively in the aerospace industry as a lightweight yet strong material. ✓Boric acic acid is used as a mild antiseptic. ✓Borax as a water softener in washing powders. ✓Borosilicate glass contains boron compounds. 55
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