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04CHM114_0402

04CHM114_0402 - CHEM 114S2004 Lecture N027April 2 CHAPTER...

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Unformatted text preview: CHEM 114S2004 Lecture N027April 2 CHAPTER 11 (concluded). ' Section 11. 7. THE (Crystalline) SOLID STATE 1. CRYSTAL STRUCTURES (a) The crystal lattice concept, and the unit cell. (Last day) Fig. 11.32 (b) The seven symmetry classes for crystals Variables are: ‘ (Last day) (c) the alternative packings of spheres Within the cubic system (simple cubic, body-centered cubic, face centered cubic) 1MPORTANT! Figs. 11.33 (Last day) Simple cubic BCC FCC (d) The common structures for metallic crystals (bcc, fcc, hcp ) iron has two..see below (e) co-ordination numbers and packing efficiencies !\ a... sng org 3 Ga. fee, 12, (3 above, 3 below and six at the side) 6 Q — bcc 8 ( 1 at each cube corner) R 3 sc6 (I ! volume of spheres/volume of box fcc, 0.74 (i. e. 74 % of space in box IS filled) 3. la! b bcc, 0.68 ‘ sc 0.52 (413310112)3 versus d3) 1:5" 3‘ U K is 3 8 1.— , 1“- ‘ “bk"!- \4) Wither-1.: d3 N9? t M '1' tit? (i) MECHANICAL PROPERTIES. (3) Elastic response: Hooke’s law and the elastic modulus 31-h." (b) plastic response, and defects m; The yield point: brittle fracture vs ductile fracture 5" 3" L; — ‘m‘* M“ 9‘3 Mk. «TC—om QMH-wl' W's-Vars‘dl, th-oM- ran-pk”... defects #5 I‘ A“ o o, o P" "* 0 £366— tfmu _ and My; “5' :31... e e t 7 ulations: (the lioltzrnann law) (EXPONENTIAL LAWS IN NATURE) Defects cost energy Ed E NUH‘.‘ h = h .t J I‘F :bfii'uu . “PL ) 09999 O." oodgo INTRINSIC VS EXTRINSIC DEFECT FORMATION ‘boe: «our team“ when... 6'" “knot-l Town was“: EQUILIBRIUM AND FR ZEN DEFECT POPULATIONS (m . f""“’ n ‘_ (“hank-M Hun “Pu;:b’r;ht: wfi‘ ‘.‘*’ 0 3' (ii) omodifying mechanical properties. | H)“ (a)W0rk hardening ‘ . m... ' 5" M 9 Ni»: 0 o. “ o \ "" M M. ’1' (b)Alloying “a L 9+” can... {.24 HQ. “OM: ‘F EA ‘froh dvqwow" SUI-cl- ‘hfll' "E (c) Quenching and tempering (to come) Types Of Solids (86011.8) Depends what sort of entity is occupying the lattice points. Qu. What sort of solid would you describe the substance C02 as forming? (a) metalic (b) molecular (c) covalent (d) ionic (a) Ionic (Coulomb interactions) structure of NaCl - two interpenetrating FCC lattices (Fig. 11.35) compare with CsCl (Fig. 11.42 ....why the difference) C 0 RM to DU M “ A1203 sapphire 3Id hardest until....ASU 3", C. 305‘! A‘“" 9-. I: A “*Nflfli 9! 30¢.» (Coulomb's law: E goes as qlqzlr) ‘ ‘M Clue-v5.0. (b) metallic (metallic bonding ..excess of bonding electrons over anti-bonding) fi Mart-M e+a~4 cm. .3 ‘5“‘a GSHL'H (c) molecular (e. g. argon (atomic) CO2 (dry ice) molecules... in each case it is can der Waals forces holding the lattice together ‘ Nah—Gout“ Oct-u." IE (d) covalent (e.g. C, Si, SiC) semiconductors GaAs “V‘vhnfl'k’ 6:45.44 ‘9)me cu..." flit lea.“ F. Infl" (The following material will be supported by a handout) ALTERNATIVE STRUCTURES FOR THE SAME SUBSTANCE. (polymorphism, and allotropy [elements] ALTERNATIVE STRUCTURES FOR THE SAME SUBSTANCE. (polymorphism, and allotropy [elements] (a) the general phenomenon The case of C_aCC_)1. .. limestone (calcite vs aragonite) 0...... may... (Mi: Mi) c414 uni-u {Law a." The stability index G (free energy. . ..details later) (i) Driving forces in Nature energy and enthalpy - .. ,, ‘* E 1: Sin-k L. 4'4“ , entropy and disorder 4-: (s to it“ Or an“; a r—II! S .$03M‘OO\ f—rv “Mo-7 and the combination G = H -TS "Flu. 9? ...
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