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Chapter 14

Chapter 14. The Group 14 Elements. Group 14 Elements. Carbon nonmetal Silicon and Germanium semimetals Tin and Lead weakly, electropositive metals. Group 14 Properties. Ability to form network covalent bonding and to catenate. Carbon (graphite). Dichlorodimethyltin(IV). Group Trends.

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Chapter 14

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  1. Chapter 14 The Group 14 Elements

  2. Group 14 Elements • Carbon • nonmetal • Silicon and Germanium • semimetals • Tin and Lead • weakly, electropositive metals

  3. Group 14 Properties • Ability to form network covalent bonding and to catenate Carbon (graphite) Dichlorodimethyltin(IV)

  4. Group Trends • Melting and boiling points

  5. Oxidation States • Multiple oxidation states are common • +4 for all the elements • covalent bonding • CO2 • -4 for C, Si, and Ge • covalent bonding • CH4 • +2 for Sn and Pb • ionic bonding • PbF2

  6. Stability of Oxidation States • Frost diagram Most stable? Most reducing? Most oxidizing?

  7. Carbon • Three common allotropes • Diamond • Graphite • Fullerenes and carbon nanotubes

  8. Diamond • Covalent network of tetrahedrally, arranged covalent bonds

  9. Diamond History • Graphite and diamond were thought to be two, different substances • In 1814, Humphry Davy burned his wife’s diamond to prove it was indeed carbon C(s) + O2(g)  CO2(g)

  10. Diamond • Electrical insulator • Very good thermal conductor • High melting point • 4000°C Regular diamond (cubic) Lonsdaleite (hexagonal)

  11. Diamonds in Nature • Found predominantly in Africa • Zaire is the largest producer • 29% • Russia • 22% • South Africa is the largest in terms of gem-quality • 17%

  12. Diamonds in Nature • Crater of Diamonds State Park • Murfreesboro, Arkansas • http://www.craterofdiamondsstatepark.com/

  13. Synthetic Diamonds • Can make synthetic diamonds from graphite by adding heat (1600°C) and pressure (5 GPa) Tracy Hall GE

  14. Synthetic Diamonds • Thin films of diamonds can be made at low temperatures Diamond “Jet” Reactor

  15. Synthetic Diamonds • New methods have become available to produce more gem-quality stones

  16. Diamond Uses • Drill bits and saws • Surgical knife coatings • Computer chip coatings • Jewlery

  17. Graphite • Hexagonal layers of covalently bound carbon • similar to benzene • delocalized pi system

  18. Graphite Layers • Very weak interactions between the layers • 335 pm interlayer distance • van der Waals radius is ~150 pm • abab arrangment

  19. Graphite Properties • Excellent conductor in two dimensions • due to the electron delocalization • Excellent lubricant • sheets “slide” • Absorber of gas

  20. Graphite Reactivity • More thermodynamically stable than diamond • More kinetically reactive than diamond • Forms intercalation compounds

  21. Graphite Sources • Mining • China • Siberia • North and South Korea

  22. Graphite Production • Acheson Process 2500°C, 30 hours

  23. Graphite Uses • Lubricants • Electrodes • Lead pencils • clay mixtures • hard mixtures “2H” • soft mixtures “HB”

  24. Fullerenes • Carbon atoms arranged in a spherical or ellipsoidal structure • five and six-membered rings C70 C60, Buckminsterfullerene

  25. Fullerenes • Named after R. Buckminster Fuller R. Buckminster Fuller (1895-1983) Buckminster Fuller’s Dome 1967 Montréal Expo

  26. Discovery of Fullerenes • David Huffman and Wolfgang Krätschmer • 1982

  27. Discovery of Fullerenes • Kroto, Curl, and Smalley

  28. Discovery of Fullerenes • Kroto, Curl, and Smalley

  29. Fullerene Production • Huffman and Krätschmer

  30. Fullerene Properties • very weak intermolecular forces • sublime when heated • soluble in most nonpolar solvents • give bright colors in solution

  31. Fullerene Properties • C60 crystal lattice (fcc) • low density, 1.5 g/cm3 • non-conductors of electricity • strong absorber of light

  32. Fullerene Chemistry • Interstitial • superconductors [Rb+]3[C603-] superconductor

  33. Fullerene Chemistry • Metal encapsulation • Li@C82 • He@C60

  34. Fullerene Chemistry • Reaction with gases C60(s) + 30F2(g)  C60F60(s)

  35. Cluster Sizes • Many different sizes

  36. Carbon Nanotubes • Sumio Iijima • 1991

  37. Nanotube Types • Single-walled (SWNT) • Multi-walled (MWNT)

  38. Nanotube Properties • excellent conductor • molecular storage

  39. Impure Carbon • Amorphous carbon (coke) • made by heating coal in an inert atmosphere • mostly graphite with some hydrogen impurities • used in iron production • removes oxygen • 5 x 108 tons per year

  40. Impure Carbon • Carbon black • fine, powdered carbon • 3.65 x 109 tons annually

  41. Impure Carbon • Activated carbon • high surface area • 103 m2/g • removes impurities from organic reactions • decolorizes chemicals

  42. Carbon Isotopes • Three isotopes • carbon-12 (98.89 %) • carbon-13 (1.11 %) • carbon-14 (0.0000001%) • radioactive • t1/2 = 5.7 x 103 years

  43. 14C Radioactive Dating

  44. Carbon Chemistry • Two important properties • catenation • a bonding capacity greater than or equal to 2 • an ability of the element to bond to itself • a kinetic inertness of the catenated compound toward or molecules and ions • multiple bonding

  45. Catenation • An ability of an element to bond with itself

  46. Bond Energies • Important in determining the reactivity and/or relative stabilities of products CH4(g) + 4F2(g)  CF4(g) + 4HF(g) not CF4(g) + 4HF(g)  CH4(g) + 4F2(g)

  47. Carbides • Binary compounds of carbon with more electropositive elements • typically hard with high melting points • three types: • ionic • covalent • metallic

  48. Ionic Carbides • Formed by the most electropositive elements • alkali and alkaline earth metals • aluminum • Only reactive carbides Na2C2(s) + 2H2O(l)  2NaOH(aq) + C2H2(g) Al4C3(s) + 12H2O(l)  4Al(OH)3(s) + 3CH4(g)

  49. Covalent Carbides • Few examples • silicon carbide and boron carbide • only important nonoxide ceramic • 7 x 105 tons produced annually SiO2(s) + 3C(s)  SiC(s) + 2CO(g)

  50. Covalent Carbides • Silicon carbide uses • grinding and polishing agents • high-temperature materials applications • mirror backings • body armor

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