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1 Liquids Molecules at interfaces behave differently than those in the interior. Molecules at surface experience a net INWARD force of attraction. This.

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Presentation on theme: "1 Liquids Molecules at interfaces behave differently than those in the interior. Molecules at surface experience a net INWARD force of attraction. This."— Presentation transcript:

1 1 Liquids Molecules at interfaces behave differently than those in the interior. Molecules at surface experience a net INWARD force of attraction. This leads to SURFACE TENSION — the energy req’d to break through the surface.

2 2 Surface Tension SURFACE TENSION also leads to spherical liquid droplets (shape of minimum surface).

3 3 Liquids Intermolec. forces also lead to CAPILLARY ACTION and to the existence of a concave meniscus for a water column in a glass tube. concave meniscus H 2 O in glass tube ADHESIVE FORCES between water and glass (with polar Si-O bonds) COHESIVE FORCES between water molecules

4 4 Capillary Action Movement of water up a piece of paper depends on H-bonds between H 2 O and the OH groups of the cellulose in the paper. Cohesive forces against the force of gravity Problem : Search for applications of capillary action in nature (plants) and in the lab (chromatography)

5 5Liquids High surface tension due to cohesive forces stronger than adhesive forces with the glass leads to the existence of a convex meniscus for a column of mercury in a glass tube. convex meniscus ADHESIVE FORCES between Hg and glass (with polar Si-O bonds) COHESIVE FORCES Non-polar mercury Hg in a glass

6 6 Viscosity VISCOSITY is the tendency or resistance of liquids to flow. Ethanol Glycerol The resistance to flow results from several factors, including intermolecular interactions, molecular shape and size. Do you expect the viscosity of glycerol to be larger or smaller than the viscosity of ethanol ?

7 7 Metallic and Ionic Solids Sections Solid-state chemistry is one of the booming areas of science, leading to the development of interesting new materials.

8 8 Types of Solids Table 13.6 TYPE CompositionBINDING FORCES Ionic NaCl, CaF 2, ZnSIon-ion MetallicNa, FeMetallic MolecularIce, I 2 Dipole Ind. dipole NetworkDiamondExtended Graphitecovalent Amorphous Glass, polyethylene Covalently bonded Networks with no Long-rangeRegularity.

9 9 Network Solids Diamond Graphite

10 10 Network Solids A comparison of diamond (pure carbon) with silicon.

11 11 Properties of Solids 1. Molecules, atoms or ions locked into a CRYSTAL LATTICE 2. Particles are CLOSE together 3. STRONG IM forces 4.Highly ordered, rigid, incompressible 5.No translations (only vibrations, or rotations on lattice sites) ZnS, zinc sulfide

12 12 Crystal Lattices Regular 3-D arrangements of equivalent LATTICE POINTS in space.Regular 3-D arrangements of equivalent LATTICE POINTS in space. Lattice points define UNIT CELLSLattice points define UNIT CELLS –smallest repeating internal unit that has the symmetry characteristic of the solid.

13 13 Cubic Unit Cells All angles are 90 degrees All sides equal length There are 7 basic crystal systems, but we are only concerned with CUBIC.

14 14 Cubic Unit Cells of Metals Figure Simple cubic (SC) Body- centered cubic (BCC) Face- centered cubic (FCC) 1 atom/unit cell 2 atoms/unit cell 4 atoms/unit cell

15 15 Units Cells for Metals Figure 13.25

16 16 Atom Packing in Unit Cells Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible.

17 17 Number of Atoms per Unit Cell Unit Cell Type Net Number Atoms Unit Cell Type Net Number Atoms SC SCBCCFCC 1 2 4

18 18 Atom Sharing at Cube Faces and Corners Atom shared in corner --> 1/8 inside each unit cell Atom shared in face --> 1/2 inside each unit cell

19 19 Simple Ionic Compounds CsCl has a SC lattice of Cs + ions with Cl - in the center. 1 unit cell has 1 Cl - ion plus (8 corners)(1/8 Cs + per corner) = 1 net Cs + ion. = 1 net Cs + ion.

20 20 Simple Ionic Compounds Salts with formula MX can have SC structure — but not salts with formula MX 2 or M 2 X

21 21 Two Views of CsCl Unit Cell Either arrangement leads to formula of 1 Cs + and 1 Cl - per unit cell

22 22 NaCl Construction FCC lattice of Cl - with Na + in holes Na + in octahedral holes

23 23 Many common salts have FCC arrangements of anions with cations in OCTAHEDRAL HOLES — e.g., salts such as CA = NaCl FCC lattice of anions ----> 4 A - /unit cellFCC lattice of anions ----> 4 A - /unit cell C + in octahedral holes ---> 1 C + at centerC + in octahedral holes ---> 1 C + at center + [12 edges 1/4 C + per edge] = 4 C + per unit cell The Sodium Chloride Lattice

24 24 Comparing NaCl and CsCl Even though their formulas have one cation and one anion, the lattices of CsCl and NaCl are different. The different lattices arise from the fact that a Cs + ion is much larger than a Na + ion.

25 25 Phase Diagrams Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line.

26 26 Phase Equilibria — Water Solid-liquid Gas-Liquid Gas-Solid

27 27 Phases Diagrams— Important Points for Water T(˚C)P(mmHg) Normal boil point Normal freeze point0760 Triple point

28 28 Solid-Liquid Equilibria In any system, if you increase P the DENSITY will go up. Therefore — as P goes up, equilibrium favors phase with the larger density (or SMALLER volume/gram). Liquid H 2 OSolid H 2 O Liquid H 2 OSolid H 2 O Density1 g/cm g/cm 3 cm 3 /gram11.09

29 29 Solid-Liquid Equilibria Raising the pressure at constant T causes water to melt. The NEGATIVE SLOPE of the S/L line is unique to H 2 O. Almost everything else has positive slope.

30 30 Solid-Vapor Equilibria At P < 4.58 mmHg and T < ˚C solid H 2 O can go directly to vapor. This process is called SUBLIMATION This is how a frost-free refrigerator works.


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