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Chapter 13

Chapter 13. The Group 13 Elements. The Elements. History. Hans Christian Oersted (1777-1851) In 1825, 3K ( Hg ) + AlCl 3 ( s )  Al( s ) + 3KCl( s ) + Hg( l ) Friedrich W öhler (1800-1882) In 1827, 3K( l ) + AlCl 3 ( s )  Al( s ) + 3KCl( s ). Group Trends. Melting and boiling points

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Chapter 13

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  1. Chapter 13 The Group 13 Elements

  2. The Elements

  3. History • Hans Christian Oersted (1777-1851) • In 1825, 3K(Hg) + AlCl3(s)  Al(s) + 3KCl(s) + Hg(l) • Friedrich Wöhler (1800-1882) • In 1827, 3K(l) + AlCl3(s)  Al(s) + 3KCl(s)

  4. Group Trends • Melting and boiling points • no apparent trend in melting points • decreasing trend in boiling points

  5. Group Trends • Melting and boiling points • each element has different arrangments in the solid phase 2180°C 660°C 30°C 157°C 303°C Boron Rhombohedral Aluminum CCP Gallium Orthorhombic Indium Tetragonal Thallium HCP

  6. Group Trends • Bond formation • favors covalent bond formation • high charge densities

  7. Group Trends • Bond formation • hydrated ions are the only stable ionic complexes • [Al(OH2)6]3+ • [Ga(OH2)6]3+ • [In(OH2)6]3+ • [Tl(OH2)6]3+

  8. Group Trends • Oxidation states • B and Al only exhibit +3 • Ga, In, and Tl exhibit both +3 and +1 • +3 most common for Ga and In • +1 most common for Tl • can have a mixed oxidation state • GaCl2 • [Ga]+[GaCl4]-

  9. Boron • Semimetal • mostly nonmetallic properties • Obtained by heating the oxide with magnesium B2O3(s) + 3Mg(l)  2B(s) + 3MgO(s) MgO(s) + 2H3O+(aq) + H2O(l)  [Mg(OH2)4]2+(aq)

  10. Boron • Natural occurrence • found most in salts around volcanic areas • borax • Na2B4O7·10H2O • [B4O5(OH)4]2- • kernite • Na2B4O7·4H2O

  11. Boron • Deposits • largest found at Boron, California • 10 km2 • beds of kernite up to 50 m thick

  12. Boron • Worldwide production • over 3 million tons • 35% used to manufacture borosilicate glass • Pyrex® • highly resistant to cracking under heat

  13. Boron • 20% used to manufacture borax • cleaning agent • NaBO3 is now more commonly used • [B2(O2)2(OH)4]2-

  14. Boron • Sodium peroxoborate [B4O5(OH)4]2-(aq) + 4H2O2(aq) + 2OH-(aq)  2[B2(O2)2(OH)4]2-(aq) + 3H2O(l) • 5 x 105 tons produced annually • used in Europe as a bleaching agent

  15. Boron • Control rods in nuclear power plants • strong absorber of neutrons • Wood preservatives • Fire-retardant in fabrics • Flux in soldering

  16. Borides • Binary compounds of boron • very hard • high melting • chemically resistant • Boron carbide • B4C (empirical) • B12C3

  17. Borides • Boron carbide • one of the hardest substances known • high tensile strength • used in bulletproof clothing • bulletproof plates in armored vehicles • bicycle frames 2B2O3(s) + 7C(s)  B4C(s) + 6CO(g)

  18. Borides • Titanium boride • TiB2 2TiO2(s) + B4C(s) + 3C(s)  2TiB2(s) + 4CO(g) • hexagonal layers of boron • Magnesium boride • superconducting

  19. Boranes • Diborane • B2H6 • 200 tons produced annually 2BF3(g) + 6NaH(s)  B2H6(g) + 6NaF(s) • highly reactive • toxic • colorless

  20. Boranes • Diborane • burns in air B2H6(g) + 3O2(g)  B2O3(s) + 3H2O(g) • reacts with water B2H6(g) + 6H2O(l)  2H3BO3(s) + 3H2(g) • undergoes hydroboration B2H6(g) + 6CH2=CHCH3(g)  2B(CH2CH2CH3)3(l)

  21. Boranes • nido-boranes • BnHn+4 • B10H14 (decaborane(14)) • arachno-boranes • BnHn+6 • B4H10 (tetraborane(10))

  22. Boranes • Was studied as a potential rocket fuel • Now, main interest is in their unique structures • B2H7- • B12H122-

  23. Sodium Tetrahydridoborate • NaBH4 • BH4- used largely in organic synthesis • reducing agent 2NaH(s) + B2H6(g)  2NaBH4(s) • sodium chloride crystal structure

  24. Boron Trifluoride • BF3 • does not dimerize • one of the strongest single bonds known • 613 kJ/mol

  25. Boron Trifluoride • Used as a Lewis acid • dative covalent bonding • “to donate”

  26. Boron Trichloride • smallest of covalently bound chlorides • gas at room temperature • reacts vigorously with water BCl3(g) + 3H2O(l)  H3BO3(aq) + 3HCl(aq)

  27. Boron Neutron Capture Theory(BNCT) • under investigation as a cancer therapy • radioactive source kills only cancerous cells • boron can easily capture a neutron • large cross-sectional area

  28. BNCT • What happens? • the energy of this process propels the atoms through cells destroying them • problems occur in getting them to the malignant cells only

  29. Aluminum • Highly, negative reduction potential (-1.66V) • highly reactive 4Al(s) + 3O2(g)  2Al2O3(s)

  30. Aluminum • Anodized • provides a thicker layer of the oxide

  31. Aluminum Uses • Construction metal • low density (2.7 g/cm3) • magnesium (1.7 g/cm3) • iron (7.9 g/cm3)

  32. Aluminum Uses • Cookware • good conductor of heat

  33. Aluminum Uses • Wiring • good conductor of electricity

  34. Aluminum Chemical Properties • Burns with oxygen and other halogens 4Al(s) + 3O2(g)  2Al2O3(s) 2Al(s) + 3F2(g)  2AlF3(s) • Amphoteric 2Al(s) + 6H+(aq)  2Al3+(aq) + 3H2(g) 2Al(s) + 2OH-(aq) + 6H2O(l)  2[Al(OH)4]-(aq) + 3H2(g)

  35. Aluminum Chemical Properties • Hydrated ions [Al(OH2)6]3+(aq) + H2O(l)  [Al(OH2)5(OH)]2+(aq) + H3O+(aq) [Al(OH2)5(OH)]2+(aq) + H2O(l)  [Al(OH2)4(OH)2] +(aq) + H3O+(aq) Aluminum chlorhydrate free

  36. Aluminum Chemical Properties • Formation of hydroxides [Al(OH2)6]3+(aq) + 3OH-(aq)  Al(OH)3(s) + 6H2O(l) Al(OH)3(s) + OH-(aq)  [Al(OH)4]-(aq) • Use as an antacid Al(OH)3(s) + 3H+(aq)  Al3+(aq) + 3H2O(l)

  37. Aluminum Availability • Most abundant metal in the Earth’s crust • commonly found in clays • aluminum silicates • mixture of sodium, potassium, iron, calcium, magnesium, and aluminum silicates • also found in bauxite • impure hydrated aluminum oxide Fe2Al9Si4O22(OH)2 Staurolite

  38. Extraction History • Henri Sainte-Claire Deville (1818-1881) • first to produce aluminum in 1854 AlCl3(s) + 3Na(s)  Al(s) + 3NaCl(s) • produced approximately 2 tons annually • price dropped 90% over 10 years

  39. Extraction History • Hall-Héroult Process (1886) P. Héroult C.M. Hall

  40. Hall-Héroult Process • Purification of bauxite • digesting with caustic soda Al2O3(s) + 2OH-(aq) + 3H2O(l)  2[Al(OH)4]-(aq) • insoluble Fe2O3 is filtered off as “red mud”

  41. Hall-Héroult Process • With cooling, hydrated aluminum oxide precipitates 2[Al(OH)4]-(aq)  Al2O3·3H2O(s) + 2OH-(aq) • The hydrate is heated to give the anhydrous aluminum oxide Al2O3·3H2O(s) + heat  Al2O3(s) + 3H2O(g)

  42. Hall-Héroult Process • Synthesis of cryolite (Na3AlF6) 3SiF4(g) + 2H2O(l)  2H2SiF6(aq) + SiO2(s) H2SiF6(aq) + 6NH3(aq) + 2H2O(l)  6NH4F(aq) + SiO2(s) 6NH4F(aq) + Na[Al(OH)4](aq) + 2NaOH(aq)  Na3AlF6(s) + 6NH3(aq) + 6H2O(l)

  43. Hall-Héroult Process • Electrolysis of a cryolite-Al2O3 solution 2Al3+(cryolite) + 6e- 2Al(l) 3O2-(cryolite) + 3C(s)  3CO(g) + 6e-

  44. Hall-Héroult Process • Four major by-products • red mud • NaOH solution is neutralized • Fe2O3 is used to extract pure iron • hydrogen fluoride gas Al2O3(s) + 6HF(g)  2AlF3(s) + 3H2O(g) • aluminum fluoride is then dissolved in cryolite

  45. Hall-Héroult Process • Four major by-products • carbon monoxide 2CO(g) + O2(g)  2CO2(g) + energy • burn with O2 to provide energy for powering the plant • fluorocarbons • 1 kg CF4 and 0.1 kg C2F6 produced for every 1 ton of Al

  46. Hall-Héroult Process • Four major by-products • Fluorocarbons • fluorosilicic acid (H2SiF6) • fluoridation of water supplies SiF62-(aq) + 8H2O(l)  H4SiO4(aq) + 4H3O+(aq) + 6F-(aq)

  47. Aluminum Producers • Major producers

  48. Aluminum Uses • 25% in the construction industry • lightweight materials • 18% in the transportation industry • lower fuel consumption • 17% in the containers and packaging industry • soda cans • 14% in the power line industry

  49. Aluminum Recycling • Uses less energy than the extraction of aluminum • melt in a smelter

  50. Aluminum Halides • AlF3 • ionic (octahedral) • melts at 1290ºC • AlCl3 • ionic character in the solid phase (hydrated octahedral) • covalent character in the liquid phase (dimer)

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