1

LiquidsLiquidsMolecules at interfaces behave differently than those in the interior.Molecules at interfaces behave differently than those in the interior.

Molecules at surface experience a net INWARD Molecules at surface experience a net INWARD force of attraction. force of attraction. This leads to This leads to SURFACE TENSIONSURFACE TENSION — the energy — the energy req’d to break through the surface.req’d to break through the surface.

2

Surface TensionSurface Tension

SURFACE TENSIONSURFACE TENSION also leads to spherical liquid also leads to spherical liquid droplets (shape of minimum surface).droplets (shape of minimum surface).

SURFACE TENSIONSURFACE TENSION also leads to spherical liquid also leads to spherical liquid droplets (shape of minimum surface).droplets (shape of minimum surface).

3

LiquidsLiquidsIntermolec. forces also lead to Intermolec. forces also lead to CAPILLARYCAPILLARY

ACTIONACTION and to the existence of a concave and to the existence of a concave meniscus for a water column in a glass tube.meniscus for a water column in a glass tube.

concavemeniscus

H2O in

glasstube

ADHESIVE FORCESbetween water and glass (with polar Si-O bonds)

COHESIVE FORCESbetween watermolecules

4

Capillary ActionCapillary Action

Movement of water up a piece of paper Movement of water up a piece of paper depends on H-bonds between Hdepends on H-bonds between H22O and O and the OH groups of the cellulose in the the OH groups of the cellulose in the paper.paper.

Cohesive forces against the force of gravityCohesive forces against the force of gravity

Problem : Search for applications of capillary action in nature (plants) and in the lab (chromatography)

5

LiquidsLiquidsHigh surface tension due to cohesive forces High surface tension due to cohesive forces

stronger than adhesive forces with the glass stronger than adhesive forces with the glass leads to the existence of a leads to the existence of a convex meniscusconvex meniscus for a column of mercury in a glass tube.for a column of mercury in a glass tube.

convexmeniscus

ADHESIVE FORCESbetween Hg and glass (with polar Si-O bonds)

COHESIVE FORCESNon-polar mercury

Hg in a glass

6

ViscosityViscosityVISCOSITY is the tendency or resistance of liquids to flow.

VISCOSITY is the tendency or resistance of liquids to flow.

Ethanol Glycerol

The resistance to flow results from several factors, includingintermolecular interactions, molecular shape and size.

Do you expect the viscosity of glycerol to be larger or smaller than the viscosity of ethanol ?

7Metallic and Ionic Metallic and Ionic SolidsSolids

Sections 13.6-8Sections 13.6-8

Metallic and Ionic Metallic and Ionic SolidsSolids

Sections 13.6-8Sections 13.6-8Solid-state chemistry is one of the booming areas of science, leading to the development of interesting new materials.

8Types of SolidsTypes of SolidsTable 13.6Table 13.6

TYPETYPE Composition Composition BINDING BINDING FORCESFORCES

Ionic Ionic NaCl, CaFNaCl, CaF22, ZnS, ZnS Ion-ionIon-ion

MetallicMetallic Na, FeNa, Fe MetallicMetallic

MolecularMolecular Ice, IIce, I22 DipoleDipole

Ind. dipoleInd. dipole

NetworkNetwork DiamondDiamond ExtendedExtendedGraphiteGraphite covalentcovalent

AmorphousAmorphous

Glass, polyethyleneGlass, polyethylene Covalently bondedCovalently bondedNetworks with noNetworks with noLong-range Long-range Regularity.Regularity.

9

Network SolidsNetwork Solids

DiamondDiamond

GraphiteGraphite

10

Network SolidsNetwork Solids

A comparison of diamond (pure carbon) A comparison of diamond (pure carbon) with silicon.with silicon.

11

Properties of SolidsProperties of Solids1. Molecules, atoms or ions 1. Molecules, atoms or ions

locked into a locked into a CRYSTAL CRYSTAL LATTICELATTICE

2. Particles are CLOSE together2. Particles are CLOSE together

3. STRONG IM forces3. STRONG IM forces

4.4. Highly ordered, rigid, Highly ordered, rigid, incompressibleincompressible

5.5. No translations (only No translations (only vibrations, or rotations on vibrations, or rotations on lattice sites) lattice sites)

ZnS, zinc sulfideZnS, zinc sulfide

12

Crystal LatticesCrystal Lattices• Regular 3-D arrangements of equivalent Regular 3-D arrangements of equivalent

LATTICE POINTS in space.LATTICE POINTS in space.• Lattice points define Lattice points define UNIT CELLSUNIT CELLS

– smallest repeating internal unit that has the symmetry smallest repeating internal unit that has the symmetry characteristic of the solid. characteristic of the solid.

13

Cubic Unit CellsCubic Unit Cells

All anglesare 90 degrees

All sidesequal length

There are 7 basic crystal systems, but we are There are 7 basic crystal systems, but we are

only concerned withonly concerned with CUBICCUBIC..

14Cubic Unit Cells of Cubic Unit Cells of MetalsMetalsFigure 13.24Figure 13.24

Simple cubic (SC)Simple cubic (SC)

Body-Body-centered centered cubic (BCC)cubic (BCC)

Face-Face-centered centered cubic (FCC)cubic (FCC)

1 atom/unit cell

2 atoms/unit cell

4 atoms/unit cell

15

Units Cells for MetalsUnits Cells for Metals

Figure 13.25Figure 13.25

16Atom Packing in Unit Atom Packing in Unit CellsCells

Assume atoms are hard spheres and that crystals are built Assume atoms are hard spheres and that crystals are built by by PACKINGPACKING of these spheres as efficiently as possible. of these spheres as efficiently as possible.

17Number of Atoms per Unit Number of Atoms per Unit CellCell

Unit Cell Type Unit Cell Type Net Number AtomsNet Number Atoms SC SC BCCBCC FCCFCC

112244

18

Atom Sharing Atom Sharing at Cube Faces and Cornersat 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

Simple Ionic CompoundsSimple Ionic Compounds

CsCl has a SC lattice of CsCl has a SC lattice of CsCs++ ions with Cl ions with Cl-- in the in the center.center.

1 unit cell has 1 Cl1 unit cell has 1 Cl-- ion ion plus plus

(8 corners)(1/8 Cs(8 corners)(1/8 Cs++ per per corner)corner)

= 1 net Cs= 1 net Cs++ ion. ion.

20

Simple Ionic Simple Ionic CompoundsCompounds

Salts with formula Salts with formula MX can have SC MX can have SC structure — but structure — but not salts with not salts with formula MXformula MX22 or M or M22XX

21

Two Views of CsCl Unit Two Views of CsCl Unit CellCell

Either arrangement leads to formula of 1 Cs+ and 1 Cl- per unit cell

22

NaCl ConstructionNaCl Construction

FCC lattice of Cl- with Na+ in holes

NaNa++ in in octahedral octahedral holesholes

23

Many common salts have FCC arrangements Many common salts have FCC arrangements of anions with cations in of anions with cations in OCTAHEDRAL OCTAHEDRAL HOLESHOLES — e.g., salts such as CA = NaCl — e.g., salts such as CA = NaCl

•• FCC lattice of anions ----> 4 AFCC lattice of anions ----> 4 A--/unit cell/unit cell

•• CC++ in octahedral holes ---> 1 C in octahedral holes ---> 1 C++ at center at center

+ [12 edges • 1/4 C+ [12 edges • 1/4 C++ per edge] per edge]

= 4 C= 4 C++ per unit cell per unit cell

The Sodium Chloride The Sodium Chloride LatticeLattice

24

Comparing NaCl and Comparing NaCl and CsClCsCl

• 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.

25Phase DiagramsPhase Diagrams

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

26

Phase Equilibria — WaterPhase Equilibria — Water

Solid-liquidSolid-liquidGas-LiquidGas-Liquid

Gas-SolidGas-Solid

27

Phases Phases Diagrams—Diagrams—

Important Points Important Points for Waterfor Water

T(˚C)T(˚C) P(mmHg)P(mmHg)

Normal boil point Normal boil point 100100 760760

Normal freeze pointNormal freeze point 00 760760

Triple point Triple point 0.00980.0098 4.58 4.58

28

Solid-Liquid EquilibriaSolid-Liquid EquilibriaIn any system, if you increase P the In any system, if you increase P the DENSITYDENSITY

will go up. will go up.

Therefore — as P goes up, equilibrium favors Therefore — as P goes up, equilibrium favors phase with the larger density (or phase with the larger density (or SMALLERSMALLER volume/gram).volume/gram).

Liquid HLiquid H22OO Solid HSolid H22OO

DensityDensity 1 g/cm1 g/cm33 0.917 g/cm0.917 g/cm33

cmcm33/gram/gram 11 1.091.09

LIQUID H2OICEfavored atlow P

favored athigh P

LIQUID H2OICEfavored atlow P

favored athigh P

29

Solid-Liquid EquilibriaSolid-Liquid Equilibria

Raising the pressure at Raising the pressure at constant T causes constant T causes water to melt.water to melt.

The NEGATIVE SLOPE The NEGATIVE SLOPE of the S/L line is of the S/L line is unique to Hunique to H22O. O.

Almost everything Almost everything else has positive else has positive slope.slope.

SolidH2O

LiquidH2O

P

T

760mmHg

0 ÞC

Normalfreezingpoint

LIQUID H2OICEfavored atlow P

favored athigh P

LIQUID H2OICEfavored atlow P

favored athigh P

30

Solid-Vapor EquilibriaSolid-Vapor EquilibriaAt P < 4.58 mmHg and T < 0.0098 ˚CAt P < 4.58 mmHg and T < 0.0098 ˚C

solid Hsolid H22O can go directly to vapor. This O can go directly to vapor. This

process is called process is called SUBLIMATIONSUBLIMATION

This is how a frost-free refrigerator works.This is how a frost-free refrigerator works.