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1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 21 The Chemistry.

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Presentation on theme: "1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 21 The Chemistry."— Presentation transcript:

1 1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 21 The Chemistry of the Main Group Elements © 2006 Brooks/Cole Thomson Lectures written by John Kotz

2 2 © 2006 Brooks/Cole - Thomson Chapter 21 Chemistry of Main Group Elements

3 3 © 2006 Brooks/Cole - Thomson Abundance of Main Group Elements Note low abundance of Li, Be, and B See also alternation of abundance with atomic number. Even atomic number = more abundant

4 4 © 2006 Brooks/Cole - Thomson HYDROGEN CHEMISTRY Hindenburg: A German dirigible filed with H 2 gas. Hindenburg crashed in New Jersey after a trans- Atlantic flight in May, Of 62 people, about half escaped uninjured. Hindenburg: A German dirigible filed with H 2 gas. Hindenburg crashed in New Jersey after a trans- Atlantic flight in May, Of 62 people, about half escaped uninjured.

5 5 © 2006 Brooks/Cole - Thomson HYDROGEN CHEMISTRY A modern use of H 2 in the Space Shuttle.A modern use of H 2 in the Space Shuttle. The rocket engine in the Shuttle itself is fueled by H 2 + O 2.The rocket engine in the Shuttle itself is fueled by H 2 + O 2. A modern use of H 2 in the Space Shuttle.A modern use of H 2 in the Space Shuttle. The rocket engine in the Shuttle itself is fueled by H 2 + O 2.The rocket engine in the Shuttle itself is fueled by H 2 + O 2.

6 6 © 2006 Brooks/Cole - Thomson Hydrogen and Oxygen

7 7 © 2006 Brooks/Cole - Thomson Hydrogen Isotopes 1 H amu protium 1 H amu protium 2 H = D deuterium 2 H = D deuterium 3 H = T tritium 3 H = T tritium Half-life of tritium = yearsHalf-life of tritium = years

8 8 © 2006 Brooks/Cole - Thomson Tritium The tritium content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.

9 9 © 2006 Brooks/Cole - Thomson Water Gas Also called “synthesis gas.”Also called “synthesis gas.” Treat coal with steamTreat coal with steam C + H 2 O --> H 2 + COC + H 2 O --> H 2 + CO Synthesis gas is the mixture of H 2 and CO.Synthesis gas is the mixture of H 2 and CO. Much of the organic chemicals industry is changing to synthesis gasMuch of the organic chemicals industry is changing to synthesis gas

10 10 © 2006 Brooks/Cole - Thomson Catalytic Steam Hydrocarbon Reforming C 3 H H 2 O Æ 3 CO + 7 H 2 Done at 900 ˚C over a catalyst Water gas shift reaction produces additional H 2 from CO CO + H 2 O ---> CO 2 + H 2 Most H 2 is now produced by the steam reforming process using methane.

11 11 © 2006 Brooks/Cole - Thomson Electrolysis of Water H 2 O ---> H 2 + 1/2 O 2 Not widely used — a)expensive b)engineering problems

12 12 © 2006 Brooks/Cole - Thomson Lab Prep of H 2 Metal + Acid Al + NaOH

13 13 © 2006 Brooks/Cole - Thomson Reactions of H 2 Virtually every element (except Group 8) will form compounds with H.Virtually every element (except Group 8) will form compounds with H. See reaction with Br 2 to give HBr.See reaction with Br 2 to give HBr.

14 14 © 2006 Brooks/Cole - Thomson Haber Process N H 2 --> 2 NH 3 Fritz Haber

15 15 © 2006 Brooks/Cole - Thomson Fuel Cells: H 2 as a Fuel Fuel cell - reactants are supplied continuously from an external source.Fuel cell - reactants are supplied continuously from an external source. Cars can use electricity generated by H 2 /O 2 fuel cells.Cars can use electricity generated by H 2 /O 2 fuel cells. H 2 carried in tanks or generated from hydrocarbons.H 2 carried in tanks or generated from hydrocarbons.

16 16 © 2006 Brooks/Cole - Thomson Hydrogen— Air Fuel Cell Figure 20.12

17 17 © 2006 Brooks/Cole - Thomson H 2 as a Fuel Comparison of the volumes of substances required to store 4 kg of hydrogen relative to car size. (Energy, p. 290)

18 18 © 2006 Brooks/Cole - Thomson Storing H 2 as a Fuel One way to store H 2 is to adsorb the gas onto a metal or metal alloy. (Energy, p. 290)

19 19 © 2006 Brooks/Cole - Thomson Sodium and Potassium The important characteristic of Group 1A elements is their vigorous reaction with water.The important characteristic of Group 1A elements is their vigorous reaction with water. K and water

20 20 © 2006 Brooks/Cole - Thomson All of the Group 1A metals are relatively soft and can be cut with a knife.All of the Group 1A metals are relatively soft and can be cut with a knife. Sodium and Potassium

21 21 © 2006 Brooks/Cole - Thomson Sodium Preparation Na is prepared by the electrolysis of molten Na in a “Downs cell”

22 22 © 2006 Brooks/Cole - Thomson Reactions with O 2 2 Na(s) + O 2 (g) ---> Na 2 O 2 (s)2 Na(s) + O 2 (g) ---> Na 2 O 2 (s) –Sodium peroxide K(s) + O 2 (g) ---> KO 2 (s)K(s) + O 2 (g) ---> KO 2 (s) –Potassium superoxide KO 2 used in breathing apparatusKO 2 used in breathing apparatus 4 KO 2 (g) + 2 CO 2 (g) ---> 2 K 2 CO 3 (s) + 3 O 2 (g)4 KO 2 (g) + 2 CO 2 (g) ---> 2 K 2 CO 3 (s) + 3 O 2 (g)

23 23 © 2006 Brooks/Cole - Thomson Na-Containing Compounds Na 2 CO 3 : soda ash or washing sodaNa 2 CO 3 : soda ash or washing soda Used as an industrial base, in making soap, and in making glass.Used as an industrial base, in making soap, and in making glass. Was made by “Solvay process” but now mined as trona : Na 2 CO 3 NaHCO 3 2H 2 OWas made by “Solvay process” but now mined as trona : Na 2 CO 3 NaHCO 3 2H 2 O Trona mine in CA

24 24 © 2006 Brooks/Cole - Thomson Alkaline Earth Elements Ca and Mg 5th and 7th in abundance on Earth.

25 25 © 2006 Brooks/Cole - Thomson Alkaline Earth Elements Be, Ca, Mg, Sr, Ba Celestite, SrSO 4

26 26 © 2006 Brooks/Cole - Thomson Magnesium from the Sea

27 27 © 2006 Brooks/Cole - Thomson Calcium Minerals: CaF 2 CaF 2 (fluorite) used in making steel. Removes impurities from molten iron.CaF 2 (fluorite) used in making steel. Removes impurities from molten iron. CaF 2 is a source of HF. CaF 2 + H 2 SO 4 ---> 2 HF + CaSO 4CaF 2 is a source of HF. CaF 2 + H 2 SO 4 ---> 2 HF + CaSO 4

28 28 © 2006 Brooks/Cole - Thomson Calcium Minerals: CaCO 3 CaCO 3 + heat ---> CO 2 + CaOCaCO 3 + heat ---> CO 2 + CaO Limestone is mostly CaCO 3.Limestone is mostly CaCO 3. Heating CaCO 3 gives lime, CaOHeating CaCO 3 gives lime, CaO CaO + H 2 O ---> Ca(OH) 2, slaked limeCaO + H 2 O ---> Ca(OH) 2, slaked lime Ca(OH) 2 is the most used industrial base.Ca(OH) 2 is the most used industrial base. CaCO 3 used in cement, fertilizer, and in making steel.CaCO 3 used in cement, fertilizer, and in making steel.

29 29 © 2006 Brooks/Cole - Thomson Calcium Minerals: CaCO 3 Mortar -- a mixture of lime, sand, and water -- has been used for hundreds of years.Mortar -- a mixture of lime, sand, and water -- has been used for hundreds of years. Reactions involved:Reactions involved: –CaO + H 2 O ---> Ca(OH) 2, slaked lime –Ca(OH) 2 + CO 2 --->CaCO 3 + H 2 O Sand grains bound together by CaCO 3Sand grains bound together by CaCO 3

30 30 © 2006 Brooks/Cole - Thomson Calcium Minerals: CaCO 3 Hard water contains dissolved Ca 2+ and Mg 2+Hard water contains dissolved Ca 2+ and Mg 2+ CaCO 3 + H 2 O + CO 2 Ca HCO 3 -CaCO 3 + H 2 O + CO 2 Ca HCO 3 - If CO 2 is removed by boiling, CaCO 3 precipitates.If CO 2 is removed by boiling, CaCO 3 precipitates.

31 31 © 2006 Brooks/Cole - Thomson Calcium Minerals: CaCO 3 CaCO 3 dissolved in presence of CO 2 Figure 16.2

32 32 © 2006 Brooks/Cole - Thomson Removing Ca 2+ an Mg 2+ by Ion Exchange Environment, p. 1002

33 33 © 2006 Brooks/Cole - Thomson Chlorophyll, a molecule with Mg 2+

34 34 © 2006 Brooks/Cole - Thomson Group 3A Chemistry Boron, aluminum, gallium, indium, thalium “20 mule team borax” wagon in Death Valley and a borax sample

35 35 © 2006 Brooks/Cole - Thomson Gems & Minerals Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet.Sapphire: Al 2 O 3 with Fe 3+ or Ti 3+ impurity gives blue whereas V 3+ gives violet. Ruby: Al 2 O 3 with Cr 3+ impurityRuby: Al 2 O 3 with Cr 3+ impurity

36 36 © 2006 Brooks/Cole - Thomson Group 3A—General Aspects All have ns 2 np 1All have ns 2 np 1 Maximum oxidation number is +3Maximum oxidation number is +3 –But Tl + exists and is poisonous All are metals except BAll are metals except B Abundances vary greatlyAbundances vary greatly –B10 ppm –Al82,000 ppm –Ga18 ppm –In/Tl< 1 Gallium

37 37 © 2006 Brooks/Cole - Thomson Group 3A—General Aspects Diagonal relation LiBeB MgAlSi Al and Be are similar in that both form amphoteric hydroxides and inert oxides.Al and Be are similar in that both form amphoteric hydroxides and inert oxides. B and Si form acidic hydroxides [ B(OH) 3 and Si(OH) 4 ] and both form volatile hydrides (B 2 H 6 and SiH 4 )B and Si form acidic hydroxides [ B(OH) 3 and Si(OH) 4 ] and both form volatile hydrides (B 2 H 6 and SiH 4 )

38 38 © 2006 Brooks/Cole - Thomson Sources of the Elements Boron—borax, Na 2 B 4 O 7 10H 2 OBoron—borax, Na 2 B 4 O 7 10H 2 O Has been used for centuries to braze metals (and mummify the dead).Has been used for centuries to braze metals (and mummify the dead). Production of ca. 2.6 x 10 6 tons annuallyProduction of ca. 2.6 x 10 6 tons annually

39 39 © 2006 Brooks/Cole - Thomson Boron Recovery B 2 O Mg ---> 2 B + 3 MgOB 2 O Mg ---> 2 B + 3 MgO –Impure B produced this way 2 BBr H 2 ---> 2 B + 6 HBr2 BBr H 2 ---> 2 B + 6 HBr –BBr 3 vapor + H 2 over hot Ta wire gives B whiskers.

40 40 © 2006 Brooks/Cole - Thomson Elemental Boron Pure boron consists of interconnected icosahedra

41 41 © 2006 Brooks/Cole - Thomson Aluminum 95% of the 90 million tons of bauxite mined is used in the Bayer process to give Al 2 O 3 (corundum)95% of the 90 million tons of bauxite mined is used in the Bayer process to give Al 2 O 3 (corundum) 90% of the oxide is converted to Al metal90% of the oxide is converted to Al metal Unit cell of Al

42 42 © 2006 Brooks/Cole - Thomson Aluminum—Bayer Process

43 43 © 2006 Brooks/Cole - Thomson Aluminum Metal Al obtained by electrolysis of Al 2 O 3 /Na 2 AlF 6 mixtureAl obtained by electrolysis of Al 2 O 3 /Na 2 AlF 6 mixture –Na 2 AlF 6 is CRYOLITE Called the Hall-Heroult processCalled the Hall-Heroult process Charles M. Hall ( )Charles M. Hall ( ) h/cmharticle.htmlhttp://www.oberlin.edu/chem/history/cm h/cmharticle.html

44 44 © 2006 Brooks/Cole - Thomson Al Production by Electrolysis

45 45 © 2006 Brooks/Cole - Thomson Aluminum Metal Main use is as structural materialMain use is as structural material –Strength, low density, corrosion resistance Strength improved by ALLOYINGStrength improved by ALLOYING –Mn: cooking utensils, furniture, roofing –Cu: truck and plane parts

46 46 © 2006 Brooks/Cole - Thomson Aluminum Metal Corrosion resistance due to aluminum oxide coating. 4 Al(s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) ∆H˚ = – 3351 kJ This illustrates the great reducing power of aluminum.

47 47 © 2006 Brooks/Cole - Thomson Corrosion of Aluminum Al metal can be oxidized if the protective Al 2 O 3 coating is breachedAl metal can be oxidized if the protective Al 2 O 3 coating is breached. Al is oxidized by Cu 2+ in a NaCl solution.

48 48 © 2006 Brooks/Cole - Thomson Aluminum Metal 4 Al(s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) ∆H˚ = kJ Solid booster rocket fuel for Space Shuttle uses Al as reducing agent and NH 4 ClO 4 as oxidizer.

49 49 © 2006 Brooks/Cole - Thomson Group 3A Hydrides—Boranes Boranes = B x H yBoranes = B x H y Began in 1912 with Alfred StockBegan in 1912 with Alfred Stock See Stock’s book “Hydrides of Boron and Silicon”See Stock’s book “Hydrides of Boron and Silicon” Good account of Hg poisoning from Hg fumes in the labGood account of Hg poisoning from Hg fumes in the lab Alfred Stock,

50 50 © 2006 Brooks/Cole - Thomson Mercury Poisoning “Among the unpleasant accidents must be reckoned the fact that, through years of working with mercury apparatus, my collaborators contracted chronic mercurial poisoning. …[It] reveals itself as an affection of the nerves, causing headaches, numbness, mental lassitude, depression, and loss of memory; such are very disturbing to one engaged in an intellectual occupation.” Alfred Stock, “Hydrides of Boron and Silicon”, 1933

51 51 © 2006 Brooks/Cole - Thomson Diborane, B 2 H 6 2 NaBH H 3 PO 4 -->2 NaBH H 3 PO 4 --> B 2 H NaH 2 PO H 2 2 NaBH 4 + I 2 (in ether) -->2 NaBH 4 + I 2 (in ether) --> B 2 H NaI + H 2 B 2 H NaI + H 2 Mp = ˚C and Bp = ˚CMp = ˚C and Bp = ˚C ∆H˚ f = kJ/mol∆H˚ f = kJ/mol B 2 H O 2 --> B 2 O H 2 O kJB 2 H O 2 --> B 2 O H 2 O kJ Higher ∆H combustion than any other fuel (per gram) than H 2Higher ∆H combustion than any other fuel (per gram) than H 2

52 52 © 2006 Brooks/Cole - Thomson Diborane Structure An “electron- deficient” compoundAn “electron- deficient” compound 12 valence e- but 8 “apparent” bonds.12 valence e- but 8 “apparent” bonds. External H-B-H angle = 121.8˚ Internal H-B-H angle = 96.5˚

53 53 © 2006 Brooks/Cole - Thomson 3-Center, 2-Electron Bond

54 54 © 2006 Brooks/Cole - Thomson HIGHER BORANES Boranes with more than 2 B atoms can be like spider webs or closed cages.Boranes with more than 2 B atoms can be like spider webs or closed cages.

55 55 © 2006 Brooks/Cole - Thomson Commercial Uses of BH Compounds Important compound = NaBH 4Important compound = NaBH 4 Used to bleach wood pulpUsed to bleach wood pulp Electrode-less plating of metals onto plasticsElectrode-less plating of metals onto plastics –BH OH - --> H 2 BO H 2 O + 8 e - –E˚ = V Used as reducing agent in organic chemistryUsed as reducing agent in organic chemistry

56 56 © 2006 Brooks/Cole - Thomson BNCT Boron Neutron Capture Therapy 10 B isotope (not 11 B) has the ability to capture slow neutrons 10 B isotope (not 11 B) has the ability to capture slow neutrons In BNCT, tumor cells preferentially take up a boron compound, and subsequent irradiation by slow neutrons kills the cells via the energetic 10 B --> 7 Li neutron capture reaction (that produces a photon and an alpha particle)In BNCT, tumor cells preferentially take up a boron compound, and subsequent irradiation by slow neutrons kills the cells via the energetic 10 B --> 7 Li neutron capture reaction (that produces a photon and an alpha particle) 10 B + 1 n ---> 7 Li + 4 He + photon 10 B + 1 n ---> 7 Li + 4 He + photon

57 57 © 2006 Brooks/Cole - Thomson Group 3A Hydroxides B(OH) 3 is an acidB(OH) 3 is an acid B(OH) 3 + H 2 O = B(OH) H +B(OH) 3 + H 2 O = B(OH) H + –K a = 7.3 x Al(OH) 3 and Ga(OH) 3 are amphotericAl(OH) 3 and Ga(OH) 3 are amphoteric Al 3+ (aq) is a weak acidAl 3+ (aq) is a weak acid –Al(H 2 O) 6 3+ = [Al(H 2 O) 5 (OH)] 2+ + H + –K a = 7.9 x 10 -6

58 58 © 2006 Brooks/Cole - Thomson Boron-Oxygen Compounds Boron is never found in nature bonded to any other element than O.Boron is never found in nature bonded to any other element than O. Borax, Na 2 B 4 O 7 10H 2 OBorax, Na 2 B 4 O 7 10H 2 O Note 6-membered rings All borates are fragments of of this structure. Na 2 [B 4 O 5 (OH) 4 ]H 2 O

59 59 © 2006 Brooks/Cole - Thomson Boron-Nitrogen Compounds ElementBCN Valence e-345 Electroneg Radius pm

60 60 © 2006 Brooks/Cole - Thomson Borazine—Analog of Benzene Borazine: Mol. wt. = 80.5 Mp = -57 ˚C; Bp = 55 ˚C B—N = 144 pm Benzene: Mol. wt. = 78.1 Mp = 6 ˚C; Bp = 80 ˚C C—C = 142 pm

61 61 © 2006 Brooks/Cole - Thomson Boron Halides Mp, ˚CBp, ˚C BF BF BCl BCl BBr BBr BI BI All are volatile All are volatile Monomeric - contrast with BX 3 and Al 2 X 6 Monomeric - contrast with BX 3 and Al 2 X 6

62 62 © 2006 Brooks/Cole - Thomson All Form Lewis Acid-Base Complexes Order of Lewis acidity: BF 3 < BCl 3 < BBr 3 < BI 3

63 63 © 2006 Brooks/Cole - Thomson All Form Lewis Acid-Base Complexes Order of Lewis acidity: BF 3 < BCl 3 < BBr 3 < BI 3 Order of acidity is inverse of expectation due to a small degree of B—X π bonding

64 64 © 2006 Brooks/Cole - Thomson Aluminum Halides CompoundAlF 3 AlCl 3 AlBr 3 AlI 3 Mp, ˚C Subl. Temp Synthesis Al 2 O HF ---> 2 AlF H 2 O 2 Al + 3 X 2 ---> 2 AlX 3 (for X = Cl, Br, I)

65 65 © 2006 Brooks/Cole - Thomson Synthesis of Al 2 Br 6 2 Al + 3 Br 2 ---> Al 2 Br 6

66 66 © 2006 Brooks/Cole - Thomson Aluminum Fluoride AlF 3 is a lattice of Al 3+ and F - ions Octahedral Al 3+ F - bridges Found in cryolite, Na 2 AlF 6

67 67 © 2006 Brooks/Cole - Thomson AlX 3 where X = Cl, Br, I Solid AlCl 3 is a layer lattice of 6- coordinate Al 3+ ions. At mp the solid volume increases 85% and electrical conductivity decreases In liquid and gas phase AlCl 3 is dimer. AlBr 3 and AlI 3 are dimers in all phases.

68 68 © 2006 Brooks/Cole - Thomson Aluminum in Water Purification Aluminum sulfate is the most important Al compound after Al(OH) 3 and Al 2 O 3. Aluminum sulfate is the most important Al compound after Al(OH) 3 and Al 2 O 3. Used in paper industry and as a flocculant in water purification. Used in paper industry and as a flocculant in water purification. As pH increases, associated species form. Their large charge nucleates fine, suspended dirt particles. As pH increases, associated species form. Their large charge nucleates fine, suspended dirt particles.

69 69 © 2006 Brooks/Cole - Thomson Aluminum Hydroxide & Oxide Many different forms  Al 2 O 3 Corundum  -AlO(OH)Diaspore  -Al(OH) 3 Bayerite  -Al 2 O 3  -AlO(OH)Boehmite  -Al(OH) 3 Gibbsite

70 70 © 2006 Brooks/Cole - Thomson Corundum:  -Al 2 O 3 Very hard—so used as an abrasive in sandpaper and toothpasteVery hard—so used as an abrasive in sandpaper and toothpaste Emery = Al 2 O 3 + Fe 2 O 3 / SiO 2Emery = Al 2 O 3 + Fe 2 O 3 / SiO 2 Chemically inert and insulatingChemically inert and insulating –Used in refractories and ceramics

71 71 © 2006 Brooks/Cole - Thomson Group 4A C, Si, Ge, Sn, PbC, Si, Ge, Sn, Pb General featuresGeneral features –Moving away from metallic character –ns 2 np 2 configurations –“inert pair” effect leads to Ge 2+, Sn 2+, Pb 2+

72 72 © 2006 Brooks/Cole - Thomson Carbon Allotropes: Graphite Layers of 6-member carbon rings.Layers of 6-member carbon rings. sp 2 C atomssp 2 C atoms Extended π bonding throughout the layers.Extended π bonding throughout the layers.

73 73 © 2006 Brooks/Cole - Thomson Graphite

74 74 Carbon Allotropes: Diamond 6-member carbon rings.6-member carbon rings. Tetrahedral sp 3 C atomsTetrahedral sp 3 C atoms Bonding extends throughout the crystal.Bonding extends throughout the crystal.

75 75 © 2006 Brooks/Cole - Thomson Diamond

76 76 Properties of Graphite and Diamond AllotropeGraphiteDiamondAllotropeGraphiteDiamond Density g/cm 3Density g/cm 3 Hardness<110 MohsHardness<110 Mohs ∆H˚ f kJ/mol∆H˚ f kJ/mol Graphite has high electrical conductivityGraphite has high electrical conductivity Diamond—has highest thermal conductivity of any known materialDiamond—has highest thermal conductivity of any known material


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