Chapter XX Modern Materials

PAGE CHAPTER 25: MODERN MATERIALS

CHAPTER 25: MODERN MATERIALS

25.3 The monomer must have a triple bond.

25.4 As with all -olefins, there are three possible isomers: isotactic, syndiotactic and atactic.

25.5 There are two possible isomers, depending on whether the two H atoms in the double bond are cis- or trans-.

25.6 There are two possible polymers, but if they are long enough, the difference would be negligible.

25.9 (1) Produce the alkoxide:

Sc(s) + 2C2H5OH(l) Sc(OC2H5)(alc) + 2H+(alc)("alc" indicates a solution in alcohol)(2) Hydrolyze to produce hydroxide pellets:

Sc(OC2H5)(alc) + 2H2O(l) Sc(OH)2(s) + 2C2H5OH(alc)(3) Sinter pellets to produce ceramic: Sc(OH)2(s) ScO(s) + 2H2O(g)

25.10

SiO2(s) + 2MeOH(l) O2Si(MeO)2(alc) + 2H+(alc) (MeOH = CH3OH)O2Si(MeO)2(alc) + 2H2O(l) O2Si(OH)2(s) + 2MeOH(alc)

Condensation: 2O2Si(OH)2(s) O2(OH)Si-O-Si(OH)O2(s) + H2O(l) etc.

25.11 Bakelite is best described as a themosetting composite polymer.

25.14 (a) This long, flat, relatively rigid molecule would likely form a liquid crystal.

(b) This molecule has a long, flexible tail and probably would not form a liquid crystal.

(c) This molecule is too compact to form a liquid crystal.

25.15 No. These polymers are too flexible, and liquid crystals require long, relatively rigid molecules.

25.16 If both the cation and anion were long, narrow, rigid, high molecular weight ions which carried small, delocalized charges, then yes.

25.19 As shown, it is an alternating condensation copolymer of the polyester class.

25.20 Advantage: a ceramic may be cheaper and more durable than metal in some cases.

Disadvantage: it is easier to produce pure metals, whereas ceramics can retain leftover chemicals from manufacture. Ceramics can also be more brittle than metal, so they are not recommended for molar crowns.

25.21 Metal amalgams expand with age; composite fillings tend to shrink.

25.24 STM requires an electrical conductor, AFM does not. Graphite conducts, diamond does not.

25.25 Each carbon atom is attached to three other carbon atoms in a (near) plane. Thus, sp2 hybrids are used.

25.26 The delocalized -electrons in graphite sheets conduct electricity, but the localized -electrons in diamond do not. In terms of band theory, it is the energy separation between the valence band and conduction band which determines whether a material is conducting, semiconducting, or insulating. In diamond, there is a large gap between the -bonding and *-antibonding orbitals that create the valence and conduction bands. This produces an insulator. With graphite (and nanotubes), C-sp2 hybridization creates and * molecular orbitals which become valence and conduction bands with a smaller gap, so these materials are semiconductors.

25.27 Graphite sheets and carbon nanotubes are both attracted to one another by dispersion forces.

25.30 The total valence shell electron count must equal 8:

(a) Ga and Sb (3+5) yes(b) As and N (5+5) no

(c) B and P (3+5) yes(d) Zn and Sb (2+5) no

(e) Cd and S (2+6) yes25.31 (a) 4 + 5: n-type (one more e()

(b) 4 + 3: p-type (one less e()

25.32 Electrons in the p-layer return to the n-layer, while electrons in the n-layer enter the external circuit.

25.35 BSCCO-2212 is Bi2Sr2CaCu2O8, composed of the ions Bi3+, Sr2+, Ca2+, Cu2+ and O2-BSCCO-2201 would therefore be Bi2Sr2Ca0Cu1O6 or Bi2Sr2CuO625.36 In the superconductive parts (assuming there are also non-superconductive parts): little or no heat would be generated, so fewer or smaller cooling devices (e.g., fans) would be required; Current flow requires no energy input, so a single battery charge would last much longer;switches would be faster, so the CPU could run at a very high rate.

25.37 Two are +2 ([Ar] 3d9), one is +3 ([Ar] 3d8). The +3 oxidation state is unusual for copper.

25.38

These categories are certainly not unique; there is an infinite variety of hybrid block/graft polymer types.

25.39

25.40 It is a condensation polyamide.

25.41 In a plastic (organic) polymer, there are covalent bonds, disulfide (covalent) bonds, H-bonds and dispersion forces. In ceramics, there are mostly ionic and network covalent bonds.

25.42

25.43 Fluoroapatite is less soluble than hydroxyapatite, particularly in acidic solutions. Dental fillings must also be insoluble.

25.44 It is amphoteric, since it reacts with both acid and base (OR = alkoxide)M(OR)n + nH+(aq) Mn+(aq) + nHORM(OR)n + nOH((aq) M(OH)n + nOR(25.45 The molecule is long, flat and rigid, so it should form a liquid crystal.

25.46 The green light has a shorter wavelength (higher energy) than red, so the LED in the exit sign has the greater band gap.

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