Dr. S. M. Condren

Polonium-210 Poisoning#atoms Po210 = (1.0gPo210Cl2) (1g/106g)

(6.02x1023atoms/mol) (1mol/280gPoCl2)

= 2.2x1015 atomst1/2 = 138 days by decay of 5.3MeV energy

10a few hundred atoms Po-110 per cellEven if only 10% decay, 110 decays per cell

Chemical & Engineering News, Dec. 4, 2006 pg.15

Former Russian spy died 22 days after the poisoning incident.The Po210 would decay by a little more than 10% in 22 days.

Dr. S. M. Condren

Chapter 13

Intermolecular Forces: Liquids, and Solids

Dr. S. M. Condren

WHY?• Why is water usually a liquid

and not a gas? • Why does liquid water boil at

such a high temperature for such a small molecule?

• Why does ice float on water?• Why do snowflakes have 6

sides?

• Why is I2 a solid whereas Cl2 is a gas?

• Why are NaCl crystals little cubes?

Dr. S. M. Condren

Now turn to forces between molecules

— INTERmolecular forces.

Forces between molecules/atoms, between ions, or between molecules/atoms and ions.

Inter-molecular ForcesHave studied INTRAmolecular forces— the forces holding atoms together to form molecules.

Dr. S. M. Condren

Dr. S. M. Condren

NaNa++—Cl—Cl-- in salt in salt

These are the strongest forces.

Lead to solids with Lead to solids with high melting high melting temperatures.temperatures.

NaCl, mp = 800 oC

MgO, mp = 2800 MgO, mp = 2800 ooCC

Ion-Ion Forces for comparison of magnitude

Dr. S. M. Condren

C–H, 413 kJ/molC–H, 413 kJ/mol

C=C, 610 kJ/molC=C, 610 kJ/mol

C–C, 346 kJ/molC–C, 346 kJ/mol

CN, 887 kJ/molCN, 887 kJ/mol

Covalent Bonding Forcesfor comparison of magnitude

Dr. S. M. Condren

Water is highly polar and Water is highly polar and can interact with positive can interact with positive and negative ions to give and negative ions to give

hydrated ions in water.ions in water.

HH

water dipole

••

••

O-

+

Attraction Between Ionsand Permanent Dipoles

Dr. S. M. Condren

Many metal ions are hydrated. Many metal ions are hydrated. This is the reason metal salts This is the reason metal salts dissolve in waterdissolve in water..

Attraction Between Ionsand Permanent Dipoles

Dr. S. M. Condren

Attraction between ions and dipole depends Attraction between ions and dipole depends on on ion charge and and ion-dipole distance..

Measured by ∆H for Measured by ∆H for

MMn+n+ + xH + xH22O O --> [M(H [M(H22O)O)xx]]n+n+

-1922 kJ/mol-1922 kJ/mol -405 kJ/mol-405 kJ/mol -263 kJ/mol-263 kJ/mol

OH

H+

-• • • O

H

H+

-• • • O

H

H+

-• • •

Na+Mg2+

Cs+

Attraction Between Ionsand Permanent Dipoles

Dr. S. M. Condren

Such forces bind molecules Such forces bind molecules having permanent dipoles to one having permanent dipoles to one another.another.

Dipole-Dipole Forces

Dr. S. M. Condren

Influence of dipole-dipole forces is seen Influence of dipole-dipole forces is seen in the boiling points of simple in the boiling points of simple molecules.molecules.

Comp’dComp’d Mol. Wt.Mol. Wt. Boil PointBoil Point

NN22 2828 -196 -196 ooCC

COCO 2828 -192 -192 ooCC

BrBr22 160160 59 59 ooCC

IClICl 162162 97 97 ooCC

Dipole-Dipole Forces

Dr. S. M. Condren

A special form of dipole-dipole A special form of dipole-dipole attraction, which enhances dipole-attraction, which enhances dipole-dipole attractions.dipole attractions.

Hydrogen Bonding

H-bonding is strongest when X and Y are N, O, or F

Dr. S. M. Condren

H-bondH-bondH-bondH-bond--

++

--

H-Bonding BetweenMethanol and Water

Dr. S. M. Condren

H-bondH-bondH-bondH-bond

--++

--

H-Bonding BetweenTwo Methanol Molecules

Dr. S. M. Condren

--

++ --

This H-bond leads to the formation of This H-bond leads to the formation of NHNH44

++ and OH and OH--

H-Bonding BetweenAmmonia and Water

H-bond

Dr. S. M. Condren

H-bonding is H-bonding is especially strong in especially strong in water becausewater because

• the O—H bond is the O—H bond is very polarvery polar

• there are 2 lone there are 2 lone pairs on the O atompairs on the O atom

Accounts for many of Accounts for many of water’s unique water’s unique properties.properties.

Hydrogen Bonding in H2O

Dr. S. M. Condren

Ice has open Ice has open lattice-like lattice-like structure.structure.

Ice density is Ice density is < liquid.< liquid.

And so solid And so solid floats on floats on water.water.

Hydrogen Bonding in H2O

Dr. S. M. CondrenDr. S. M. Condren

Hydrogen Bonding in Snowflakes

Dr. S. M. CondrenDr. S. M. Condren

Hydrogen Bonding in Snowflakes

Dr. S. M. Condren

Logo for ICE

Dr. S. M. Condren

Ice has open lattice-like structure.Ice has open lattice-like structure.

Ice density is < liquid and so solid floats on water.Ice density is < liquid and so solid floats on water.

One of the VERY few One of the VERY few substances where substances where solid is LESS DENSE solid is LESS DENSE than the liquid.than the liquid.

Hydrogen Bonding in H2O

Dr. S. M. Condren

A consequence ofhydrogen bonding

Dr. S. M. Condren

H bonds ---> abnormally high specific heat of water (4.184 J/g•K)H bonds ---> abnormally high specific heat of water (4.184 J/g•K)

This is the reason water is used to put out fires,This is the reason water is used to put out fires,

it is the reason it is the reason lakes/oceans lakes/oceans control climate,control climate,

and is the reason and is the reason thunderstorms thunderstorms release huge release huge amounts of energy.amounts of energy.

Hydrogen Bonding in H2O

Dr. S. M. Condren

Lower 9th Ward of New Orleans

10 months after the storm!

Dr. S. M. Condren

Boiling Points of Simple Hydrogen-Containing Compounds

Dr. S. M. Condren

Methane Hydrate

Dr. S. M. Condren

H-bonding is especially strong in biological systems H-bonding is especially strong in biological systems — such as DNA. — such as DNA.

DNA — helical chains of phosphate groups and DNA — helical chains of phosphate groups and sugar molecules. Chains are helical because of sugar molecules. Chains are helical because of tetrahedral geometry of P, C, and O.tetrahedral geometry of P, C, and O.

Chains bind to one another by specific hydrogen Chains bind to one another by specific hydrogen bonding between pairs of Lewis bases.bonding between pairs of Lewis bases.

——adenine with thymineadenine with thymine

——guanine with cytosineguanine with cytosine

Hydrogen Bonding in Biology

Dr. S. M. Condren

Portion of a Portion of a DNA chainDNA chain

Double helix Double helix of DNAof DNA

Dr. S. M. Condren

Base-Pairing through H-Bonds

Dr. S. M. Condren

Base-Pairing through H-Bonds

Dr. S. M. Condren

James Watson (left)James Watson (left)1928-1928-Francis Crick (right)Francis Crick (right)1916-20041916-2004

Rosalind Franklin, Rosalind Franklin, 1920-19581920-1958X-ray photo that led X-ray photo that led to structureto structure

Maurice Wilkins, Maurice Wilkins, 1916 - 20041916 - 2004

1962 Nobel Prize for Physiology or Medicine

Discovering the Double Helix

Dr. S. M. Condren

How can non-polar molecules such as How can non-polar molecules such as OO2 2 and Iand I22 dissolve in water? dissolve in water?The water dipole The water dipole INDUCES a dipole a dipole in the Oin the O22 electric cloud. electric cloud.

Dipole-induced Dipole-induced dipoledipole

Dipole-induced Dipole-induced dipoledipole

Forces Involving Induced Dipoles

Dr. S. M. Condren

Solubility increases Solubility increases with mass of the gaswith mass of the gas

Forces Involving Induced Dipoles

Process of inducing a dipole is Process of inducing a dipole is polarization..

Degree to which electron cloud of an atom or molecule can be Degree to which electron cloud of an atom or molecule can be distorted is its distorted is its polarizability..

Dr. S. M. Condren

Consider IConsider I22

dissolving dissolving in ethanol, in ethanol, CHCH33CHCH22OHOH

OH

-

+

I-I

R-

+

OH

+

-

I-I

R

The alcohol The alcohol temporarily temporarily creates or creates or INDUCESINDUCES a a dipole in Idipole in I22..

IM Forces – Induced Dipoles

Dr. S. M. Condren

The magnitude of the induced dipole The magnitude of the induced dipole depends on the tendency to be distorted. depends on the tendency to be distorted.

Higher molecular weight ---> larger Higher molecular weight ---> larger induced dipoles.induced dipoles.

MoleculeMolecule Boiling Point Boiling Point ((ooC)C)

CHCH44 (methane) (methane) - 161.5- 161.5

CC22HH66 (ethane) (ethane) - 88.6 - 88.6

CC33HH88 (propane) (propane) - 42.1- 42.1

CC44HH1010 (butane) (butane) - 0.5- 0.5

Forces Involving Induced Dipoles

Dr. S. M. Condren

Boiling Points of Hydrocarbons

Note linear relation between bp and molar mass.

CHCH44

CC22HH66

CC33HH88

CC44HH1010

Dr. S. M. Condren

Intermolecular Forces Summary

Dr. S. M. Condren

In a liquidIn a liquid•• molecules are in molecules are in

constant motionconstant motion

•• there are appreciable there are appreciable intermolec. forcesintermolec. forces

•• molecules close molecules close togethertogether

•• Liquids are almost Liquids are almost incompressibleincompressible

•• Liquids do not fill the Liquids do not fill the containercontainer

Liquids

Dr. S. M. Condren

Liquids

break IM bonds

make IM bonds

Add energy

Remove energy

LIQUID VAPOR

<---condensation

evaporation--->

The two key properties we need to The two key properties we need to describe are describe are EVAPORATION and its and its opposite—opposite—CONDENSATION

Dr. S. M. Condren

Liquids At higher T a much At higher T a much larger number of larger number of molecules has high molecules has high enough energy to enough energy to break IM forces and break IM forces and move from liquid to move from liquid to vapor state.vapor state.

High E molecules carry High E molecules carry away E. You cool away E. You cool down when sweating down when sweating or after swimming.or after swimming.

.

0

Num

ber

of m

olec

ules

Molecular energy

minimum energy neededto break IM forces and evaporate

higher Tlower T

Distribution of molecular energies in a liquid. KE is proportional to T.

Dr. S. M. Condren

LiquidsWhen molecules of liquid are in When molecules of liquid are in the vapor state, they exert a the vapor state, they exert a VAPOR PRESSURE

EQUILIBRIUM VAPOR PRESSURE is the pressure is the pressure exerted by a vapor over exerted by a vapor over a liquid in a closed a liquid in a closed container when the container when the

rate of evaporation = rate of condensation.

Dr. S. M. Condren

Measuring Equilibrium Vapor Pressure

Liquid in flask evaporates and exerts pressure on manometer.

Dr. S. M. Condren

Equilibrium Vapor Pressure

Dr. S. M. Condren

Boiling Point

When pressure is lowered, the vapor pressure When pressure is lowered, the vapor pressure can equal the external pressure at a lower can equal the external pressure at a lower temperature.temperature.

Liquid boils when its vapor pressure equals atmospheric pressure.

Dr. S. M. Condren

If external P = 760 mm Hg, T of boiling is the If external P = 760 mm Hg, T of boiling is the

NORMAL BOILING POINT

VP of a given molecule at a given T depends VP of a given molecule at a given T depends

on IM forces. Here the VP’s are in the orderon IM forces. Here the VP’s are in the order

Liquids

C2H5H5C2 HH5C2 HH

wateralcoholether

increasing strength of IM interactions

extensiveH-bondsH-bonds

dipole-dipole

OOO

Dr. S. M. Condren

LiquidsHEAT OF VAPORIZATION is the heat is the heat

required (at constant P) to vaporize the liquid.required (at constant P) to vaporize the liquid.LIQ + heat ---> VAPLIQ + heat ---> VAP

Compd.Compd. ∆H∆Hvapvap (kJ/mol) (kJ/mol) IM ForceIM Force

HH22OO 40.7 (100 40.7 (100 ooC)C) H-bonds, dipole, H-bonds, dipole, induced dipoleinduced dipole

SOSO22 26.8 (-47 26.8 (-47 ooC)C) dipole, induced dipole, induced dipole dipole

XeXe 12.6 (-107 12.6 (-107 ooC)C) induced dipole induced dipole

Dr. S. M. Condren

LiquidsMolecules at surface behave differently than those Molecules at surface behave differently than those

in the interior.in the interior.

Molecules at surface experience net INWARD force of Molecules at surface experience net INWARD force of attraction. attraction. This leads to This leads to SURFACE TENSION — the energy — the energy required to break the surface.required to break the surface.

Dr. S. M. Condren

LiquidsIntermolecular forces also lead to Intermolecular forces also lead to CAPILLARY

action and to the existence of a concave action and to the existence of a concave meniscus for a water column.meniscus for a water column.

concavemeniscus

H2O in

glasstube

ADHESIVE FORCESbetween waterand glass

COHESIVE FORCESbetween watermolecules

Dr. S. M. Condren

Capillary 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 O

and the OH groups of the cellulose in and the OH groups of the cellulose in the paper.the paper.

Dr. S. M. Condren

Metallic and Ionic Solids

Dr. S. M. Condren

Types of SolidsTYPE EXAMPLE FORCE

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

MetallicMetallic Na, Fe Na, Fe MetallicMetallic

MolecularMolecular Ice, I Ice, I22 DipoleDipole

Ind. dipole Ind. dipole

NetworkNetwork Diamond Diamond ExtendedExtended Graphite Graphite covalent covalent

Dr. S. M. Condren

Phases Diagrams —Important Points for

WaterT(˚C) P(mmHg)

Normal boil point 100 760

Normal freeze point 0 760

Triple point 0.0098 4.58

Critical point 374374 218 218 atm atm

Dr. S. M. Condren

Solid-Vapor Equilibria

At 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. O can go directly to vapor.

This process is called This process is called SUBLIMATION

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

Dr. S. M. Condren

CO2 Phase Diagram

Dr. S. M. Condren

Network Solids

DiamondDiamond

GraphiteGraphite

Dr. S. M. Condren

Properties of Solids

1.1. Molecules, atoms or ions Molecules, atoms or ions

locked into a locked into a CRYSTAL LATTICE

2. Particles are CLOSE 2. Particles are CLOSE togethertogether

3. STRONG IM forces3. STRONG IM forces

4. Highly ordered, rigid, 4. Highly ordered, rigid, incompressibleincompressible

ZnS, zinc sulfideZnS, zinc sulfide

Dr. S. M. Condren

Crystal 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 CELLS

– smallest repeating internal unit that has the smallest repeating internal unit that has the

symmetry characteristic of the solid.symmetry characteristic of the solid.

Dr. S. M. Condren

Cubic 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 CUBIC..

Dr. S. M. Condren

Cubic Unit Cells of Metals

Primitive cubic

Dr. S. M. Condren

• 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.

Simple Cubic Unit Cell

Dr. S. M. Condren

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

Dr. S. M. Condren

Number of Atoms per Unit Cell

Unit Cell Type Unit Cell Type Net Number AtomsNet Number AtomsSC (Primitive Cubic)SC (Primitive Cubic)

BCCBCC FCCFCC

112244

Primitive cubic

Dr. S. M. Condren

Atom Packing in Unit Cells

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

Dr. S. M. Condren

Units Cells for Metals

Primitive cubic

Dr. S. M. Condren

Atom Packing in Unit Cells

Dr. S. M. Condren

Simple Ionic Compounds

Lattices of many simple ionic solids are built Lattices of many simple ionic solids are built by taking a SC (Simple or Primitive Cubic) by taking a SC (Simple or Primitive Cubic) or FCC (Face-Centered Cubic) lattice of or FCC (Face-Centered Cubic) lattice of ions of one type and placing ions of ions of one type and placing ions of opposite charge in the holes in the lattice.opposite charge in the holes in the lattice.

EXAMPLE: CsCl has a SC (Primitive CsCl has a SC (Primitive Cubic) lattice of CsCubic) lattice of Cs++ ions with Cl ions with Cl-- in the in the center NOT a BCC (Body-Centered Cubic) center NOT a BCC (Body-Centered Cubic) because the ion at the center of the body because the ion at the center of the body is not the same ion as at the corners.is not the same ion as at the corners.

Dr. S. M. Condren

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

Dr. S. M. Condren

NaCl Construction

FCC lattice of Cl- with Na+ in holes

NaNa++ in in octahedral octahedral holesholes

Dr. S. M. Condren

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.

Dr. S. M. Condren

Face-Centered CubicDiamond Zinc blende

Dr. S. M. Condren

Common Ionic Solids

Magnesium silicate, MgSiO3