Intermolecular Forces, Liquids and Solids. Goals: 1.Describe intermolecular forces and their...

Intermolecular Intermolecular Forces, Forces,

Liquids and Liquids and Solids.Solids.

Goals:

1. Describe intermolecular forces and their effects.

2. List the effects of hydrogen bonding.3. List the properties of liquids.4. Draw basic cubic unit cells.5. Relate unit cells for ionic compounds to

formulas.6. List the properties of solids.7. Use phase diagrams to predict physical state

of materials.

Intermolecular ForcesIntermolecular Forces

Have studied Have studied INTRAINTRAmolecular forcesmolecular forces—the forces holding atoms together —the forces holding atoms together to form molecules.to form molecules.

Now turn to forces between molecules Now turn to forces between molecules

— — INTERINTERmolecular forces. molecular forces.

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

Liquids and SolidsLiquids and Solids

Why at atmospheric pressure and room temperature,

O2 is a gas

H2O is a liquid

C6H12O6 is a solid

- little interaction between particles: no specific volume or shape

- particles held together with sufficient force that give a volume

- particles are rigidly held in a volume and shape


• Intramolecular forces – chemical bonds – bind atoms to one another within molecules.

• Intermolecular forces – attractive forces between molecules.– Determine physical properties of liquids and

solids – without intermolecular forces there would not be liquids or solids.

– Intermolecular forces are relatively unimportant in gases because molecules are far apart (the ideal gas law assumes there are non).

Intermolecular ForcesIntermolecular Forces• Determine the physical properties of substances.

• Molecules have a tendency to remain apart from each other. Intermolecular forces of attraction overcome this tendency more effectively at low temperature (molecules have low energies) and at high pressures (molecules are close together).

• A substance is likely to exist as a gas at ________ temperatures (energetic molecules) and at _______ pressures (molecules far apart).

• A substance is likely to exist as a solid at ______ temperatures and ________________pressures (closely packed molecules).

• The liquid – in-between state – exists at intermediate temperatures and moderate to high pressures.

For comparison: Ion-Ion ForcesFor comparison: Ion-Ion Forces

Na+—Cl- in saltThese are the

strongest forces. Lead to solids with

high melting temperatures.

NaCl, mp = 800 oCMgO, mp = 2800 oC

For comparison: Covalent Bond For comparison: Covalent Bond ForcesForces

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

Summary of Intermolecular ForcesSummary of Intermolecular Forces

p. 604p. 604

Attraction between Ions and Attraction between Ions and Permanent DipolesPermanent Dipoles

Water is highly polar and can interact with positive ions to

give hydrated ions in water.

HH

water dipole

••

••

O-

+


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


Attraction between ions and dipole depends on ion _______ and ion-dipole ________.

Measured by ∆H for Mn+ + H2O --> [M(H2O)x]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 DipolesAttraction between Dipoles

Such forces bind molecules having permanent dipoles to one another.

Dipole- Dipole ForcesDipole- Dipole Forces

Influence of dipole-dipole forces is seen in the boiling points of simple molecules.Compd Mol. Wt. Boil

PointN2 28 -196 oC

CO 28 -192 oCBr2 160 59 oC

ICl 162 97 oC

Dipole- Dipole ForcesDipole- Dipole Forces

• Which has the higher boiling point?If a molecule is polar will have dipole-dipole interactions, and then the boiling point needed to break the interactions will be higher than that needed for a nonpolar molecule.

– HCl or F2

– SiH4 or PH3

Hydrogen BondingHydrogen Bonding

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

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


• A hydrogen bond between molecules is an intermolecular force in which a hydrogen atom covalently bonded to a nonmetal atom in a molecule is simultaneously attracted to a nonmetal atom of a neighboring molecule.

• The strongest hydrogen bonds are formed if the nonmetal atoms are small and highly electronegative (N, O, and F).

H2O


H-Bonding Between Methanol and Water

H-bondH-bondH-bondH-bond


H-Bonding Between Two Methanol Molecules

H-bondH-bondH-bondH-bond

--++

--

Hydrogen Bonding in WaterHydrogen Bonding in Water

H-bonding is especially strong in water because

• the O—H bond is very polar

• there are 2 lone pairs on the O atom

Accounts for many of water’s unique properties.


Ice has open lattice-like structure.

Ice density is _______ than liquid.

And so solid floats on water.


Ice has open lattice-like structure.Ice density is < liquid and so solid floats on

water.

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


• A consequence of H-bonding


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

This is the reason water is used to put out fires, it is the reason lakes/oceans control climate, and is the reason thunderstorms release huge energy.


H bonds leads to abnormally high boiling point of water.


p. 604p. 604

Boiling Points of Simple H-Boiling Points of Simple H-containing Compoundscontaining Compounds

Hydrogen Bonding in Hydrogen Bonding in BiologyBiology

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

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

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

—adenine with thymine —guanine with cytosine

Hydrogen Bonding and DNAHydrogen Bonding and DNA• Hydrogen bonding is also the force that binds the two chains of a DNA

molecule together, so hydrogen bonding is a key to understanding the replication of organisms.

Adenine and Thymine form 2 hydrogen bonds

Guanine and Cytosine form 3 hydrogen bonds

Base Pairing through Hydrogen Base Pairing through Hydrogen BondsBonds

Hydrogen BondsHydrogen Bonds

• Which has a higher boiling point?

H3C-CH3 (ethane) or H3C-OH (methanol)

H2O (water) or HCl (hydrogen chloride)

Hydrogen BondsHydrogen Bonds

• In which of the following compounds would hydrogen bonding be an important intermolecular force?

SH

H

H

H

H

F

H

H

H H

H

H

H

H

H

N

H

H

H

H

H

OH

H

H

H

O

H

H

H

c

c c

c

c

c c

Forces Involving Induced Forces Involving Induced DipolesDipoles

How can non-polar molecules such as O2 and I2 dissolve in water?

Dipole-induced Dipole-induced dipoledipole

Dipole-induced Dipole-induced dipoledipole


Solubility increases with mass the gas


• Process of inducing a dipole is ________.

• Degree to which electron cloud of an atom or molecule can be distorted in its _____________.

• The larger the molecule, the more polarizable.

Induced DipolesInduced Dipoles

Consider I2 dissolving in ethanol, CH3CH2OH

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..


Formation of a dipole in two nonpolar I2

molecules.Induced dipole-Induced dipole-induced dipoleinduced dipoleInduced dipole-Induced dipole-induced dipoleinduced dipole


The induced forces between I2 molecules

are very weak, so solid I2 sublimes (goes from a solid to gaseous molecules).


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

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

Molecule Boiling Point (oC) CH4 (methane) - 161.5

C2H6 (ethane) - 88.6

C3H8 (propane) - 42.1

C4H10 (butane) - 0.5 CHCH44

CC22HH66

CC33HH88

CC44HH1010


• Which has the higher boiling point?

Ne or Xe

C2H6 (ethane) or C4H10 (butane)

C2H5OH (ethanol) or C3H7OH (propanol)

What intermolecular force(s) must What intermolecular force(s) must be overcome to:be overcome to:

Melt ice?

Sublime solid I2?

Convert liquid NH3 to NH3 vapor?H

H

HN


Students should be familiar with identifying the types of intermolecular

forces and predicting physical properties of substances.

In Liquids:In Liquids:

• Molecules are in constant motion, but the movement is restricted by neighboring molecules (___ diffusion, compared to gases).

• Molecules of a liquid are much closer together than those of a gas (_____ compressibility).

• There are appreciable intermolec. Forces.• Liquids do not fill the container.

LiquidsLiquids

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

break IM bonds

make IM bonds

Add energy

Remove energy

LIQUID VAPOR

<---condensation<---condensation

evaporation--->evaporation--->

Liquids - EvaporationLiquids - Evaporation

To evaporate, molecules must have sufficient energy to break IM forces.

Breaking IM forces requires energy. The process of evaporation is endothermic.

Liquids – Distribution of Liquids – Distribution of EnergiesEnergies

0

Nu

mb

er o

f m

olec

ule

s

Molecular energy

higher Tlower T

See Figure 13.14See Figure 13.14

Minimum energy req’d to break IM forces and evaporate

Distribution of Distribution of molecular molecular energies in a energies in a liquid.liquid.

KE is proportional to KE is proportional to T.T.

Liquids – Distribution of Liquids – Distribution of EnergiesEnergies

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

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

Equilibrium Vapor PressureEquilibrium Vapor Pressure

Liquid in flask evaporates and exerts pressure on manometer.

Equilibrium Vapor PressureEquilibrium Vapor PressureWhen molecules of liquid are in the vapor state, they exert a VAPOR PRESSURE.

EQUILIBRIUM VAPOR PRESSURE

is the pressure exerted by a vapor over a liquid in a closed container when the rate of evaporation = the rate of condensation.System is in a state of Dynamic Equilibrium

Higher Intermolecular Forces -> Lower Vapor Pressure

Boiling PointBoiling Point• Boiling point – of a liquid is

the temperature at which its vapor pressure becomes equal to atmospheric pressure.– Increases when external

pressure is increased.

– Normal boiling point – temperature at which a liquid boils under standard pressure (1 atm).

Equilibrium Vapor PressureEquilibrium Vapor Pressure

Vapor Pressure as a function of T:Vapor Pressure as a function of T:

1. The curves show all 1. The curves show all conditions of Pconditions of P and T where LIQ and and T where LIQ and

VAP VAP are in are in EQUILIBRIUMEQUILIBRIUM2. The Vapor Pressure 2. The Vapor Pressure

risesrises with T.with T.3. When VP = external 3. When VP = external

P,P,the liquid boils.the liquid boils.

This means that BP’s of liquids change with altitude.This means that BP’s of liquids change with altitude.

Boiling at lower PressureBoiling at lower Pressure

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

Consequences of Vapor Consequences of Vapor Pressure ChangesPressure Changes

When can cools, vapor pressure of When can cools, vapor pressure of water drops. Pressure in the can is water drops. Pressure in the can is

less than that of atmosphere, so can less than that of atmosphere, so can is crushed. is crushed.

LiquidsLiquids4. If external P = 760 mm 4. If external P = 760 mm

Hg, T of boiling is the Hg, T of boiling is the

NORMAL BOILING POINTNORMAL BOILING POINT

5.5. VP of a given molecule VP of a given molecule

at a given T depends on at a given T depends on

IM forces. Here the VP’s IM forces. Here the VP’s

are are

in the orderin the order

C2H5H5C2 HH5C2 HH

wateralcoholether

increasing strength of IM interactions

extensiveH-bondsH-bonds

dipole-dipole

OOO

LiquidsLiquids

HEAT OF VAPORIZATIONHEAT OF VAPORIZATION is the heat req’d is the heat req’d (at constant P) to vaporize the liquid.(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-bondsH-bonds

SOSO22 26.8 (-47 26.8 (-47 ooC)C) dipoledipole

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

Heat of VaporizationHeat of Vaporization• Heat is required for the conversion of a

liquid to a vapor. Some volatile liquids are used to cool the skin. When a liquid is condensed it releases heat.

• The heat of vaporization is characteristic of a given liquid.

• Molar heat of vaporization – quantity of heat required to vaporize 1 mol of a liquid at a constant pressure (units: cal/mol).

• Given the molar heat of vaporization, we can calculate the heat of vaporization in cal/g or kJ/g using the molar mass.

Clasius-Clapeyron EquationClasius-Clapeyron Equation

• Clausius-Clapeyron Clausius-Clapeyron

equation — used to find equation — used to find

∆H˚∆H˚vapvap..

• The logarithm of the The logarithm of the

vapor pressure P is vapor pressure P is

proportional to ∆Hproportional to ∆Hvaporizationvaporization

and to 1/T.and to 1/T.

ln P = –(∆H˚ln P = –(∆H˚vapvap/RT) + C/RT) + C ln

P2P1

= Hvap

R

1T1

- 1T2

Calculate the enthalpy of vaporization Calculate the enthalpy of vaporization ((HHoo

vapvap) of ethylene glycol. This compound ) of ethylene glycol. This compound has a vapor pressure of 14.9 mmHg at 373 K has a vapor pressure of 14.9 mmHg at 373 K and a vapor pressure of 49.1 mmHg at 398 and a vapor pressure of 49.1 mmHg at 398

K.K.

LiquidsLiquidsMolecules at surface behave differently than those in Molecules at surface behave differently than those in

the interior.the interior.

• Molecules at surface experience net INWARD force Molecules at surface experience net INWARD force of attraction. of attraction.

• This leads to This leads to SURFACE TENSIONSURFACE TENSION — the energy req’d — the energy req’d to break the surface.to break the surface.

Surface TensionSurface Tension

• Surface tension also leads to spherical liquid droplets.

Surface TensionSurface Tension• Surface tension – force or tension that resists

disruption (horizontal needle over water, insects over water). – A molecule at the surface of the liquid is attracted only by

molecules at its sides and below it; forces tend to pull inward and cause the liquid to contract – Small amount of liquid will “bead” to minimize its surface area.

– Soaps and other detergents act in part by lowering surface tension, enabling water to spread out and wet a solid surface.

Leaf surface without

surfactantwith

surfactant

Surface

Properties of Liquids:Properties of Liquids:

• Surface tension – force or tension that resists disruption (horizontal needle over water, insects over water).

• Viscosity – resistance to flow.

Properties of LiquidsProperties of Liquids• Viscosity – resistance to flow.

– Liquids with low viscosity (“thin liquids”) generally consist of small, symmetrical molecules with weak intermolecular forces. Viscous liquids are generally made up or large or unsymmetrical molecules with fairly strong intermolecular forces.

– Viscosity generally decreases with increasing temperature.

Hexane Octane Iso-octane

CH3

CH2

CH2

CH2

CH2

CH3 CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH3 CH3 CH2

CH CH3

CH3

CH3

CH3

Properties of LiquidsProperties of LiquidsIntermolecular forces also lead to CAPILLARY action

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

concave

meniscus

H 2 O in

glass

tube

ADHESIVE FORCES

between water

and glassCOHESIVE FORCES

between water

molecules

Movement of water up a piece of paper depends on H-bonds between H2O and the -OH groups of the cellulose in the paper.

Properties of LiquidsProperties of Liquids

• Answer with increases, decreases, or does not change:

• If the intermolecular forces in a liquid increase, the normal boiling point of the liquid .

• If the intermolecular forces in a liquid decrease, the vapor pressure of the liquid .

• If the temperature of a liquid increases, the vapor pressure .

increases

increases

increases

Metallic and Ionic SolidsMetallic and Ionic Solids

SolidsSolids• Particles (atoms, molecules, or ions) are close

together (incompressible).• In solids there is little motion other than vibration

about a fixed point (particles in liquid are in constant, restricted motion).

• An increase in temperature will increase the vigor of the vibrations in a solid. If vibrations become strong enough, the solid will melt.

• Solid crystals – stacking unit cells – portion of a crystal which represents the regular, repeating manner extending in three dimensions that atoms, ions, or molecules are organized.– Crystal lattice – framework on which a pattern is outline.

There are 14 different lattices to describe all crystalline solids.

• Amorphous solids – are solids that lack this ordered arrangement: glasses.

From Solid to Liquid: Melting From Solid to Liquid: Melting (Fusion)(Fusion)

• Melting point – temperature at which the solid becomes a liquid.

• The heat energy is absorbed by the particles of the solid; the particles vibrate with more and more vigor until, the forces holding the particles in a particular arrangement are overcome.

• A high melting point is one indication of the forces holding a solid together are very strong.

Heat of FusionHeat of Fusion

• Molar heat of fusion – quantity of heat required to convert 1 mol of a solid to liquid.

• Generally, for 1 mol of a substance, it takes more heat energy to vaporize it than to melt it. It takes more energy to vaporize the liquid because the attraction between particles must be almost completely overcome (to get to gas).

Types of SolidsTypes of Solids

TYPETYPE EXAMPLEEXAMPLE FORCEFORCE

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

MetallicMetallic Na, FeNa, Fe MetallicMetallic

MolecularMolecular Ice, IIce, I22 DipoleDipoleInd. dipoleInd. dipole

NetworkNetwork DiamondDiamond ExtendedExtendedGraphiteGraphite CovalentCovalent

Network SolidsNetwork Solids

DiamondDiamond

GraphiteGraphite

A comparison of diamond (pure carbon) with

silicon.

Network SolidsNetwork Solids

SiC also is important for tooling in the semiconductor industry, for laser mirrors, as a substrate for wear-resistant diamond coatings, as an abrasive and grinding wheel, as heating elements and igniters, as an additive for reinforcement of metals, and for numerous refractories applications.

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 smallest repeating internal unit that has the

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

Cubic Unit CellsCubic Unit Cells

There are 7 basic crystal systems, but we There are 7 basic crystal systems, but we are only concerned with CUBIC.are only concerned with CUBIC.

All anglesare 90 degrees

All sidesequal length


Very rare: Po

Fe, K, Na, Cr, Mo, W

Al, Cu, Pb, Ag


• 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.

Atom Packing in Units CellsAtom Packing in Units Cells

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

FCC is more efficient than FCC is more efficient than either BC or SC.either BC or SC.

Leads to layers of atoms.Leads to layers of atoms.

Solids can be classified by the types of Solids can be classified by the types of intermolecular forces holding the particles together:intermolecular forces holding the particles together:– Ionic solids

Have_________ at definite points in the lattice. Ionic forces are very strong.Ionic solids have ______ melting points and _____vapor pressures, and are quite hard.

– Molecular crystalsHave discrete _______________ at the lattice pointsHeld together by rather _______ dispersion forces (nonpolar), dipolar forces (polar), or hydrogen bonds (hydrogen-bonded). Molecular solids often have ________ melting points than ionic solids.

– Covalent network crystalsHave _________ at the lattice points._________ are joined into extensive networks by ______________; each crystal is in essence one large molecule.They are extremely hard and nonvolatile, melt with decomposition at _______________temperatures.

– Metallic solidsConsidered as _______________ at the lattice sites. The lost valance electrons are released and distributed throughout the lattice.Electrons can move freely about the lattice; metals are ________ conductors of heat and electricity.

Classify the SolidsClassify the SolidsSodium Chloride (NaCl) Solid Nitrogen (N2 (s) ) Copper (Cu) Quartz (SiO2)Potassium (K) Sulfur (S8)Iron (II) Sulfate (FeSO4) Brass (Copper and Zinc alloy)Ice (H2O (s)) Carbon (C) Glucose

Ionic Covalent Network Metallic Molecular(ionic compounds) (atoms in the lattice) (metals) (molecules in the lattice)

Atom Packing in Units CellsAtom Packing in Units Cells Unit Cell Type Unit Cell Type Net Number Net Number

AtomsAtoms SC SC BCCBCC FCCFCC

112244

Phase DiagramsPhase Diagrams

Transitions between PhasesTransitions between Phases

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

(At equilibrium particles move from liquid to (At equilibrium particles move from liquid to gas as fast as they move from gas to gas as fast as they move from gas to liquid, for example.)liquid, for example.)

Phase Diagram of WaterPhase Diagram of Water

Solid Solid phasephase

Liquid Liquid phasephase

Gas Gas phasephase

Phase Equilibria for WaterPhase Equilibria for WaterSolid-Solid-

liquidliquid Gas-Gas-LiquidLiquid

Gas-Gas-SolidSolid

Triple Point for WaterTriple Point for Water

At the At the TRIPLE POINT TRIPLE POINT all three all three phases are in equilibrium.phases are in equilibrium.

Critical T and PCritical T and P

.

LIQUID

GAS

Pcritical

Hig

h P

ress

ure

High Temperature

Tcritical

Note that linegoes straight up

Above Above critical T no critical T no pure liquid pure liquid exists no exists no matter how matter how high the high the pressure.pressure.

Above Above critical T no critical T no pure liquid pure liquid exists no exists no matter how matter how high the high the pressure.pressure.

As P and T increase, you finally reach As P and T increase, you finally reach

the the CRITICAL TCRITICAL T and and PP

Critical T and PCritical T and P

COMPDCOMPD TTcc((ooC)C) PPcc(atm)(atm)

HH22OO 374374 218218

COCO22 3131 7373

CHCH44 -82-82 4646

Freon-12Freon-12 112112 4141(CCl(CCl22FF22))

Notice that TNotice that Tcc and P and Pcc depend on depend on intermolecular forces.intermolecular forces.

A fluorocarbon, CF4, has a critical temperature of A fluorocarbon, CF4, has a critical temperature of -45.7 -45.7ooC, a critical pressure of 37 atm, and a C, a critical pressure of 37 atm, and a

normal bp of -128normal bp of -128ooC. Are there any conditions under C. Are there any conditions under which this compound can be a liquid at room which this compound can be a liquid at room

temperature?temperature?

COCO22 Phase Diagram Phase Diagram

COCO22 Phases Phases

Separate phases

Increasing pressure

More pressure

Supercritcal CO2

Densities are the sameDensities are the sameFor engineering purposes, supercritical fluids can be regarded as “hybrid solvents” with properties between those of gases and liquids, i.e. a solvent with a low viscosity, high diffusion rates and no surface tension

Solid-Liquid EquilibriaSolid-Liquid Equilibria

In any system, if you increase Pressure the DENSITY will go up.

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

Liquid H2O Solid H2O

Density 1 g/cm3 0.917 g/cm3

cm3/gram 1 1.09LIQUID H2OICEfavored atlow P

favored athigh P

LIQUID H2OICEfavored atlow P

favored athigh P


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

The NEGATIVE SLOPE The NEGATIVE SLOPE of the line is unique of the line is unique to Hto H22O. Almost O. Almost everything else has everything else has positive slope.positive slope.

SolidH2O

LiquidH2O

P

T

760mmHg

0 ÞC

Normalfreezingpoint


favored athigh P


favored athigh P


The behavior of water The behavior of water under pressure is an under pressure is an example of example of

LE CHATELIER’S PRINCIPLELE CHATELIER’S PRINCIPLE

At Solid/Liquid equilibrium, At Solid/Liquid equilibrium, raising P squeezes the raising P squeezes the solid. solid.

It responds by going to It responds by going to phase with greater phase with greater density, i.e., the liquid density, i.e., the liquid phase.phase.

SolidH2O

LiquidH2O

P

T

760mmHg

0 ÞC

Normalfreezingpoint

Solid-Liquid EquilibriaSolid-Liquid 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

SublimationSublimation

• Sublimation – passage of molecules directly from the solid to the vapor state.

• Deposition – the reverse process of sublimation – condensation of a vapor to a solid.

• The vapor pressure of ice at 0oC is 4.58 mmHg.• The vapor pressure of iodine at 39.4 oC is 760

mmHg (1 atm).

Water: An unusual liquidWater: An unusual liquid• At room temperature it is the only

liquid compound with a molar mass as low as 18 g/mol.

• Unlike most substances, the solid form of water (ice) is less dense than the liquid (ice remains on top layer of frozen lakes). In liquid state, water molecules are close together but randomly arranged. In ice water molecules are ordered with large hexagonal holes.

• Liquid water has a higher density than most other familiar liquids (those insoluble in water –oil - float on its surface).

2

Boi

ling

poin

t (o C

)

Period3 4 5

100

0

-100

-200

H2O

H2S H2Se

H2Te

Water: An unusual liquidWater: An unusual liquid

Structure of ice at normal atmospheric pressure. It is a hydrogen-bonded network of water molecules.

Water: An unusual liquidWater: An unusual liquid• Water has a very high specific heat (Table 7.6).

– It takes 1 cal of heat to raise the temperature of 1 g of water 1oC (10 times larger than that of iron). Water acts as a giant thermostat to moderate daily temperatures due to the large amount of heat water gives off for a drop in temperature.

• Water has a high heat of vaporization.– Large amounts of body heat, produced as a by-product

of metabolic processes, can be dissipated by the evaporation of small amounts of water (perspiration) from the skin. The heat of vaporization is obtained from the body, and the body is cooled. The water molecule is polar; in the liquid state water molecules are strongly associated by hydrogen bonding. A input of a large amount of energy is needed if vaporization is to take place.

RememberRemember

• Go over all the contents of your textbook.

• Practice with examples and with problems at the end of the chapter.

• Practice with OWL tutor.• Work on your OWL assignment for

Chapter 13.

Intermolecular Forces, Liquids and Solids. Goals: 1.Describe intermolecular forces and their...

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