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Unformatted text preview: 1/14/2008 Chem 106
Lecture 4 Chapter 13 Intermolecular Forces
Homework 1 due TODAY - deadline 11PM. 11PM. Lab section changes underway this week (PINK FORM) (PINK FORM) QUIZ 1 This FRIDAY material from last week + HW#1 Homework 2 now available on OWL H k il bl Laboratory 13 this week PRELAB ASSIGNMENT DUE at the START of TUTORIAL
1 When molecules of liquid are in the vapor state, they exert a VAPOR PRESSURE Liquids EQUILIBRIUM VAPOR PRESSURE is the pressure exerted by a vapor over a liquid in a closed container when the closed container when the rate of evaporation = the rate of condensation. 2 1 1/14/2008 Liquids
HEAT OF VAPORIZATION is the heat req'd is the heat req'd
( t (at constant P) to vaporize the liquid. t t P) t i th li id LIQ + heat > VAP LIQ + heat > VAP IM Force Compd. Hvap (kJ/mol) 40.7 (100 oC) Hbonds H2O 26.8 ( 26.8 (47 oC) ( dipole p SO2 Xe 12.6 (107 oC) 12.6 ( induced dipole Hvap can be determined with Clausius-Clapeyron EQN. Clausius3 Measuring Equilibrium Vapor Pressure Liquid in flask evaporates and exerts pressure on manometer. Active Fig. 13.17 4 2 1/14/2008 Equilibrium Vapor Pressure
Active Figure 13.18 5 Liquids Equilibrium Vapor Pressure
FIGURE 13.18: VP as a function of T. FIGURE 13.18: 1. The curves show all conditions of P and T where 1 Th h ll diti fP dT h LIQ and VAP are in EQUILIBRIUM LIQ and VAP are in EQUILIBRIUM 2. The VP rises with T. 3. When VP = external P, the liquid boils. This means that BP's of liquids change with external pressure or altitude. external pressure or altitude. 6 3 1/14/2008 Figure 13.18: VP versus T 13.18: Liquids 4. If external P = 760 mm Hg, T of boiling is the NORMAL BOILING POINT 5. VP of a given molecule at a given T depends on IM forces. Here the VP's are in the order
ether O C2H 5 H 5C2 dipoledipole alcohol O H 5C2 H H-bonds water O H H extensive H-bonds
7 increasing strength of IM interactions Boiling Point at Lower Pressure
Water t W t at 55 C Figure 13.18 When pressure is lowered, the vapor pressure can equal the external pressure at a lower temperature.
8 4 1/14/2008 Critical Temperature and Pressure
As P and T increase, you finally reach the CRITICAL T and P
Above critical T no liquid exists no matter how high the pressure. no matter how high the pressure. Beyond Tc and Pc, substance is Beyond T called a supercritical fluid. called a supercritical fluid. Density of a liquid. Viscosity of a gas. 9 Critical T and P
COMPD H2O CO2 CH4 Freon Freon12 (CCl2F2) Tc(oC) 374 31 82 112 Pc(atm) 218 73 46 41 Notice that T and P depend on intermolecular Notice that Tc and Pc depend on intermolec lar forces. 10 5 1/14/2008 Supercritical Fluids CO2 T T=T =31 T=Tc=31C 31 At P=Pc=73 atm increase temperature SF6 supercritical fluid transition Movie available on eLearning 11 IM Forces and Liquids Vaporization Vaporization condensation. Enthalpy of vaporization Vapor pressure Boiling point Critical Properties 12 6 1/14/2008 13 Types of Solids
Table 13.6 TYPE Ionic I i Metallic Molecular Network EXAMPLE NaCl, CaF2, Z S NaCl C F ZnS N Cl, CaF , ZnS Na, Fe Ice, I2 Diamond Graphite FORCE Ion Ion ion I i Metallic Dipole Ind. dipole Extended covalent 14 7 1/14/2008 Properties of Solids
1. Molecules, atoms or ions locked into a locked into a CRYSTAL LATTICE 2. Particles are CLOSE together 3. STRONG IM forces 4. Highly ordered, rigid, incompressible
ZnS, zinc sulfide
15 Crystal Lattices Regular 3D arrangements of equivalent LATTICE Regular 3 POINTS in space. L tti Lattice points define UNIT CELLS i t d fi smallest repeating internal unit that has the symmetry characteristic of the solid. 16 8 1/14/2008 Cubic Unit Cells
There are 7 basic crystal systems, one common example is There are 7 basic crystal systems, one common example is CUBIC. All sides equal length All angles are 90 degrees 17 Cubic Unit Cells of Metals
Simple cubic (SC)
Figure 13.27 BodyBodycentered cubic (BCC) FaceFacecentered cubic (FCC) Rare for metals Only Po Common Alkali metals Common Most efficient 18 Cu, Ag, Au, Ni... 9 1/14/2008 Simple Cubic Unit Cell
Figure 13.26 Each atom is at a corner of a unit cell and is shared among 8 unit cells. Each edge is shared with 4 cells Each face is part of two cells.
19 Cubic Unit Cells of Metals
Figure 13.27 20 10 1/14/2008 Atom Packing in Unit Cells
Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible. 21 13.7 Ionic Solids CsCl unit cell has a SC lattice of Cl ions with Cs+ in the center. ion plus 1 unit cell has 1 Cs+ ion plus (8 corners)(1/8 Cl per corner) = 1 net Cl ion. 11 1/14/2008 Two Views of CsCl Unit Cell
Lattice can be SC lattice of Cl with Cs+ in hole OR SC lattice of Cs+ with Cl in hole Either arrangement leads to formula of 1 Cs and 1 Cl per unit cell Either arrangement leads to formula of 1 Cs+ and 1 Cl per unit cell The Sodium Chloride Lattice
Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL HOLES -- e.g., salts such as CA = NaCl e g salts such as CA NaCl FCC lattice of anions > 4 A/unit cell FCC lattice of anions > 4 A in octahedral holes > 1 C C+ in octahedral holes > 1 C+ at center + [12 edges 1/4 C+ per edge] = 4 C+ per unit cell 12 1/14/2008 Octahedral Holes - FCC Lattice Common Ionic Solids Zinc sulfide, ZnS Zinc sulfide, ZnS Th S2 i The S ions are in i TETRAHEDRAL holes in the Zn2+ FCC lattice. This gives 4 net Zn2+ ions and 4 net S ions and 4 net S2 ions. S2 Figure 13.33 ZnS FCC Unit cell with Tetrahedral holes 13 ...
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This note was uploaded on 06/24/2008 for the course CHEM 106 taught by Professor Bruce during the Spring '08 term at Washington State University .
- Spring '08