Chapter 10 Chapter 10 Liquids and SolidsLiquids and Solids

TopicsTopics Intermolecular forcesIntermolecular forces

– Dipole-dipole forcesDipole-dipole forces Hydrogen bondingHydrogen bonding

– London ForcesLondon Forces The liquid stateThe liquid state

– Surface tensionSurface tension– Capillary actionCapillary action– ViscosityViscosity

An introduction to structures and types of solidsAn introduction to structures and types of solids– X-ray analysis of solidsX-ray analysis of solids– Types of crystalline solidsTypes of crystalline solids

Structure and bonding in metalsStructure and bonding in metals– Bonding metals for metals Bonding metals for metals – Meta alloysMeta alloys

Molecular solidsMolecular solids Ionic solidsIonic solids Vapor pressure and changes of stateVapor pressure and changes of state Phase diagramsPhase diagrams

10.510.5 Section is self studySection is self study

Intra- vs. Inter-molecular forcesIntra- vs. Inter-molecular forces

intramolecular forcesintramolecular forces– inside molecules (bonding)inside molecules (bonding)– hold atoms together into moleculehold atoms together into molecule

intermolecular forcesintermolecular forces– These are what hold the molecules together in the These are what hold the molecules together in the

condensed states.condensed states.– Forces between moleculesForces between molecules– They get weaker as phase changes from S – L – GThey get weaker as phase changes from S – L – G

When a substance changes state, molecule stays together When a substance changes state, molecule stays together but intermolecular forces are but intermolecular forces are weakenedweakened

10.1 Intermolecular Forces10.1 Intermolecular Forces

Intermolecular ForcesIntermolecular Forces

GasesGases – fill container, random rapid motion, never coming to rest or clustering together• Motion is mainly translational

LiquidsLiquids – fixed volume, flow and assume shape of container, only slightly compressible, stronger forces hold molecules together• Motion is mainly translationalMotion is mainly translational

Solids – fixed volume, definite shape, generally less compressible than liquids, forces hold particles in a fixed shape

• Motion is mainly vibrational

Intermolecular Forces

Intermolecular forces are attractive forces between molecules

Intramolecular forces hold atoms together in a molecule.

Intermolecular vs Intramolecular

• 41 kJ to vaporize 1 mole of water (inter)

• 930 kJ to break all O-H bonds in 1 mole of water (intra)

Generally, intermolecular forces are much weaker than intramolecular forces.

“Measure” of intermolecular force

boiling point

melting point

Hvap

Hfus

Hsub

Dipole – Dipole FocesDipole – Dipole Foces

Molecules that line up in the presence of a electric Molecules that line up in the presence of a electric field are dipoles. field are dipoles.

The opposite ends of the dipole can attract each The opposite ends of the dipole can attract each other so the molecules stay close together.other so the molecules stay close together.

1% as strong as covalent bonds1% as strong as covalent bonds Small role in gases.Small role in gases. Molecules with these forces possess higher Molecules with these forces possess higher

melting points and boiling points than nonpolar melting points and boiling points than nonpolar molecules of comparable molar massmolecules of comparable molar mass

The strengths of intermolecular forcesintermolecular forces are generally weaker than either ionic or covalent bonds.

16 kJ/mol (to separate molecules)

431 kJ/mol (to break bond)

++-

-

Polar molecules have dipole-dipole attractions for one another.

Intermolecular forces between molecules that posses dipole moment

Dipole-dipole forces: (polar molecules)

SO O.. ::

....

:

+

--

..:

..

--

SO O:

..:

+

dipole-dipole attraction

What effect does this attraction have on the boiling point?

Nonpolar PolarMolecule MM BP Molecule MM BP

N2 28 -196 CO 28 -192

SiH4 32 -112 PH3 34 -88

GeH4 77 -90 AsH3 78 -62

Br2 160 69 ICl 162 97

Effect of polarity on boiling points

• Effect of polarity is usually small enough to be obscured by differences in molar mass

HCl -85BP (oC)

HBr -60

HI -30

BP increase although polarity decreases

Hydrogen BondsHydrogen Bonds

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

• The strongest hydrogen bonds are formed if the nonmetal

atoms are smallsmall and highly electronegativehighly electronegative – e.g., N, O, F

very strong type of dipole-dipole attractionvery strong type of dipole-dipole attraction–because bond is so polarbecause bond is so polar–because atoms are so smallbecause atoms are so small

Hydrogen bonding: It is very strong dipole-dipole interaction (bonds involving H-F, H-O, and H-N are most important cases).

+H-F- --- +H-F-

Hydrogen bonding

Hydrogen bondHydrogen bond

Cl(HCl)Cl(HCl) and and S(HS(H22S)S) do not form hydrogen do not form hydrogen

bonding although they have bonding although they have electronegativity similar to N, why? electronegativity similar to N, why? – They are of bigger size to approach the They are of bigger size to approach the

hydrogen atomhydrogen atom

Hydrogen bond is 5-10% as strong as the Hydrogen bond is 5-10% as strong as the covalent bondcovalent bond

Hydrogen bonding between water molecules

WaterWater

+

-

+

Hydrogen BondingHydrogen Bonding

• Bonding between hydrogen and more electronegative neighboring atoms such as oxygen and nitrogen

Hydrogen bonding between ammonia and water

Hydrogen Bonding EffectsHydrogen Bonding Effects

• Solid water is less dense than liquid water due to hydrogen bonding

• Hydrogen bonding is also the reason for the unusually high boiling point of water

The larger the molecule the larger the Van der Waals attraction due to more electrons in the molecule.

The stronger the attraction, the higher the boiling point.

Boiling Points for Some Non Polar MoleculesBoiling Points for Some Non Polar Molecules

CH4

SiH4

GeH4SnH4

PH3

NH3 SbH3

AsH3

H2O

H2SH2Se

H2Te

HF

HI

HBrHCl

Boilin

g Poin

ts

0ºC

100

-100

200Molar massMolar mass

Hydrogen Bonding in other moleculesHydrogen Bonding in other molecules

Many organic acids can form dimers due to hydrogen bonding

Certain organic molecules can also form an intramolecular hydrogen bond

Ethanol shows hydrogen bonding

O

H

CH3 C O H

H

H CH2 CH3

Do these compounds show hydrogen bonding?

A. NH

H

N

H

H (Hydrazine)

B. CH3 C CH3

O

(Acetone)

C. CH3 O CH3 (dimethyl ether)

Do these compounds show hydrogen bonding?

Hydrogen bonding and solubilityHydrogen bonding and solubility

Some compounds containing O, N & F show Some compounds containing O, N & F show

high solubilities in certain hydrogen high solubilities in certain hydrogen containing solvents.containing solvents.

NHNH33 & CH & CH33OH dissolves in HOH dissolves in H22O through the O through the

formation of H-bondsformation of H-bonds

N

H

H

H

OH

H

CH

H

H

O

H

OH

H

London Dispersion ForcesLondon Dispersion Forces

Non - polar molecules also exert forces on each Non - polar molecules also exert forces on each other.other.

Otherwise, no solids or liquids.Otherwise, no solids or liquids. Electrons are not evenly distributed at Electrons are not evenly distributed at

every instant in time.every instant in time. Thus, they will have an instantaneous dipole.Thus, they will have an instantaneous dipole. Atom with instantaneous dipole induces a dipole in Atom with instantaneous dipole induces a dipole in

the atom next to it.the atom next to it. As a result, induced dipole- induced dipole As a result, induced dipole- induced dipole

interaction would take place. interaction would take place. London forces increase with the size of the London forces increase with the size of the

molecules. molecules.

“Electrons are shifted to overload one side of an atom or molecule”.

+ +- -

attraction

London Dispersion ForcesLondon Dispersion Forces

They exist in every molecular compoundThey exist in every molecular compound They are significant only for nonpolar They are significant only for nonpolar

molecules and noble gas atomsmolecules and noble gas atoms They are weak, short-livedThey are weak, short-lived Caused by formation of temporary dipole Caused by formation of temporary dipole

momentsmoments

- The ease with which electron “cloud” of an atom The ease with which electron “cloud” of an atom can be distorted is called can be distorted is called polarizabilitypolarizability..

Polarizability: the ease with which an atom or molecule can be distorted to have an instantaneous dipole. “squashiness”

In general big moleculesare more easily polarized

than little ones.

London Dispersion ForcesLondon Dispersion Forces

Weak, short lived.Weak, short lived. Lasts longer at low temperature.Lasts longer at low temperature. Eventually long enough to make liquids.Eventually long enough to make liquids. More electrons, more polarizable.More electrons, more polarizable. Bigger molecules, higher melting and Bigger molecules, higher melting and

boiling points.boiling points. Much, much weaker than other forces.Much, much weaker than other forces. Also called Also called Van der Waal’s forcesVan der Waal’s forces..

RelativeRelative Magnitudes of ForcesMagnitudes of Forces

The types of bonding forces vary in their The types of bonding forces vary in their strength as measured by average bond strength as measured by average bond energy. energy.

Covalent bonds (400 kcal/mol)

Hydrogen bonding (12-16 kcal/mol )

Dipole-dipole interactions (2-0.5 kcal/mol)

London forces (less than 1 kcal/mol)

Strongest Weakest

Halogen Boiling Pt (K)

Noble Gas Boiling Pt (K)

F2 85.1 He 4.6

Cl2 238.6 Ne 27.3

Br2 332.0 Ar 87.5

I2 457.6 Kr 120.9

Which one(s) of the above are most polarizable?Hint: look at the relative sizes.

London Forces in HydrocarbonsLondon Forces in Hydrocarbons

10.210.2 The Liquid stateThe Liquid state

Properties of LiquidsProperties of LiquidsLow compressibilityLow compressibilityLack of rigidityLack of rigidityHigh density compared to gasesHigh density compared to gasesBeading (beads up as droplets) Beading (beads up as droplets) Surface tensionSurface tensionCapillary actionCapillary actionViscosityViscosity

Stronger intermolecular forces cause Stronger intermolecular forces cause each of these to increase.each of these to increase.

Surface tensionSurface tension

The resistance to an The resistance to an increase in its surface increase in its surface areaarea

Polar molecules and Polar molecules and liquid metalsliquid metals

show high surfaceshow high surface

tensiontension

Surface tensionSurface tension

Molecules in Molecules in the middle are the middle are attracted in all attracted in all directions.directions.

Molecules at the the top are only pulled inside.

Minimizes surface area.

Surface tensionSurface tension

AllAll liquids have surface tension liquids have surface tension– water is just higher than most otherswater is just higher than most others

How can we decrease surface How can we decrease surface tension?tension?– Use a Use a surfactantsurfactant - - sursurface face actactive ive aagegentnt– Also called a wetting agent, like Also called a wetting agent, like

detergent or soapdetergent or soap– Interferes with hydrogen bondingInterferes with hydrogen bonding

Adhesive forcesAdhesive forces are intermolecular forces between unlike molecules

Cohesive forcesCohesive forces are intermolecular forces between like molecules

BeadingBeading

If a polar substance is If a polar substance is placed on a non-polar placed on a non-polar surface. surface. – There are cohesive,There are cohesive,– But no adhesive forces.But no adhesive forces.

And Visa VersaAnd Visa Versa

Capillary ActionCapillary Action

Capillary action results fromCapillary action results from

intermolecular interactionsintermolecular interactions Liquids spontaneously rise in a narrow Liquids spontaneously rise in a narrow

tube.tube. Glass is polar.Glass is polar. It attracts water molecules (adhesive It attracts water molecules (adhesive

forces)forces)

Glass has polar Glass has polar molecules.molecules.

Glass can also Glass can also hydrogen bond.hydrogen bond.

This attracts the This attracts the water molecules.water molecules.

Some of the pull is Some of the pull is up a cylinderup a cylinder..

Water curves up along Water curves up along the side of glass.the side of glass.

This makes the This makes the meniscusmeniscus, as in a , as in a graduated cylindergraduated cylinder

Plastics are non-Plastics are non-wetting; no attractionwetting; no attraction

MeniscusMeniscus

In Glass In Plastic

ViscosityViscosity

Viscosity is a measure of a liquid’s resistance to flow

–strong inter molecular strong inter molecular forces forces highly viscous highly viscous–large, complex molecules large, complex molecules highly viscous highly viscous–Cyclohexane has a lower Cyclohexane has a lower viscosity than hexane.viscosity than hexane.–Because it is a circle- Because it is a circle- more compact.more compact.

10.3 An introduction to structures 10.3 An introduction to structures and types of solidsand types of solids

Types of SolidsTypes of Solids

Crystalline SolidsCrystalline Solids: : highly regular three dimensional highly regular three dimensional arrangement of their components arrangement of their components [[table salt table salt ((NaClNaCl))]]

Amorphous solidsAmorphous solids: : considerable disorder in their considerable disorder in their structures structures ((glass: components are frozen in place glass: components are frozen in place before solidifying and achieving an ordered before solidifying and achieving an ordered arrangementarrangement))

The positions of components in a crystalline solid are The positions of components in a crystalline solid are usually represented by a lattice usually represented by a lattice

Crystalline solidsAmorphous solids

Representation of Components Representation of Components in a Crystalline Solidin a Crystalline Solid

LatticeLattice: : A 3-dimensional system that describes the locations of components A 3-dimensional system that describes the locations of components ((atoms, ions, or moleculesatoms, ions, or molecules) ) that make up the unit cells of a substancethat make up the unit cells of a substance..Unit CellUnit Cell: The smallest repeating unit in the lattice: The smallest repeating unit in the lattice..There are There are ThreeThree common types of unit cells: common types of unit cells:

– simple cubicsimple cubic– bodybody--centered cubiccentered cubic– faceface--centered cubiccentered cubic

Crystal Structures - Crystal Structures - CubicCubic

a

aa

SimpleSimple Face-CenteredFace-Centered Body-CenteredBody-Centered

Unit CellsUnit Cells

The simple cubic cell is the simplest unit cell and has structural particles centered only at its corners

The body-centered cubic (bcc) structure has an additional structural particle at the center of the cube

TheThe face-centered face-centered cubic (fcc)cubic (fcc) structure structure has an additional has an additional structural particle at structural particle at the center of each the center of each faceface

CubicCubic

Unit cells in 3 dimensions

At lattice points:

•Atoms

•Molecules

•Ions

lattice points

The simple cubic cell is the simplest unit cell and has structural particles centered only at its corners

Body-Centered CubicBody-Centered Cubic

Unit cells in 3 dimensions

The body-centered cubic

(bcc) structure has an additional structural particle at the center of the cube

Face-Centered CubicFace-Centered CubicThe face-centered cubic (fcc) structure has an additional structural particle at the center of each face

• Sample is powdered• X-rays of single wavelength is used• Distance between planes of atoms in the crystal are calculated from the angles at which the rays are diffracted using Bragg equation

X-Ray analysis of solids

Spots from diffracted X-rays

Spot from incident beam

X-Ray analysis of solids

X-Ray diffraction

Extra distance traveled by lower ray = BC + CD = n = 2d sin

Reflection of X-rays from two layers of atoms

1st layer of atoms

2nd layer of atoms

n = 2d sin

Bragg EquationBragg Equation

nn 2 = 2 = dd sin sin

dd = = distance between atomsdistance between atoms nn = = an integeran integer = = wavelength of the xwavelength of the x--raysrays

When silver crystallizes, it forms face-centered cubic cells. The unit cell edge length is 408.7 pm. Calculate the density of silver.

d = mV

V = a3 = (408.7 pm)3 = 6.78X107 pm3

___ atoms/unit cell in a face-centered cubic cell

m = 4 Ag atoms107.9 gmole Ag

x1 mole Ag

6.022 x 1023 atomsx = 1.79X10-22 g

d = mV

7.17 x 10-22 g6.83 x 10-23 cm3

= = 1.79X10-22 g / 6.78X107 pm3

= 2.6X10-30 g/pm3

Types of crystalline SolidsTypes of crystalline Solids Ionic solids Ionic solids (ionic compounds)(ionic compounds)

– Ions (held by electrostatic attraction) at point in Ions (held by electrostatic attraction) at point in latticelattice

– They conduct electric current when dissolved in They conduct electric current when dissolved in waterwater

Molecular solids Molecular solids (molecular compounds)(molecular compounds)– Molecules (held by: dispersion and/or dipole-Molecules (held by: dispersion and/or dipole-

dipole forces) at each point in lattice. Ice is a dipole forces) at each point in lattice. Ice is a molecular solid Hmolecular solid H22OO

atomic solids atomic solids (metals, nonmetals, noble gases)(metals, nonmetals, noble gases) – Elements (C, B, Si) that are composed of atoms at Elements (C, B, Si) that are composed of atoms at

lattice points. Three types: lattice points. Three types: – Metallic– metallic bondMetallic– metallic bond– Network – strong covalent bondingNetwork – strong covalent bonding– Group 8A –London Dispersion ForcesGroup 8A –London Dispersion Forces

10.410.4 Structure and Bonding of MetalsStructure and Bonding of Metals

Physical properties of metalsPhysical properties of metals Ionization energy Ionization energy E is small (outer electrons move E is small (outer electrons move

relatively free); this results inrelatively free); this results in– High electrical conductivityHigh electrical conductivity– High thermal conductivityHigh thermal conductivity– They areThey are

Ductile: can be drawn oust into wiresDuctile: can be drawn oust into wires Malleable:Malleable: can be hammered into thin sheetscan be hammered into thin sheets

Electrons act like a glue holding atomic nucleiElectrons act like a glue holding atomic nuclei Crystals of nonmetals break into small pieces if it is Crystals of nonmetals break into small pieces if it is

hammered (brittle)hammered (brittle) They have luster (reflect light)They have luster (reflect light) They form alloysThey form alloys

Metallic CrystalsMetallic Crystals

Can be viewed as containing Can be viewed as containing atoms (spheres) packed atoms (spheres) packed together in the together in the closest closest arrangementarrangement possible possible

The spheres are packed in The spheres are packed in layerslayers

Closest packing-Closest packing- when each when each sphere has 12 neighborssphere has 12 neighbors

– 6 on the same plane6 on the same plane– 3 in the plane above3 in the plane above– 3 in the plane below3 in the plane below

Packing in CrystalsPacking in Crystals

“Open” packing has larger voids in between particles compared to close-packed crystals

Closest packed structures

It has (aba) arrangements that occur when the spheres of the third layer occupy positions so that each sphere in the third layer lies directly over a sphere in the first layer

Hexagonal closest-packed (hcp) structure

Closest packed structuresClosest packed structures

It has (abc) arrangement that occurs when the spheres of the third layer occupy positions that NO sphere lies over one in the first layer

Cubic closest-packed (ccp) structure

An atom in every fourth layerlies over an atom in the First layer

Net number of spheres (atoms) in a unit cell, length of Net number of spheres (atoms) in a unit cell, length of the edge of the cell, density of the closest packed solidthe edge of the cell, density of the closest packed solid

Face centered cubic cellFace centered cubic cell Atoms occupy corners and centers of the facesAtoms occupy corners and centers of the faces Atoms at the corners do not touch each otherAtoms at the corners do not touch each other Atoms contact is made at the face diagonalAtoms contact is made at the face diagonal 74% of the space is occupied74% of the space is occupied Ca, Sr, transition metalsCa, Sr, transition metals An atom at the center of the face of cube is shared by An atom at the center of the face of cube is shared by

another cube that touches that face.another cube that touches that face. Only Only atom is assigned to a given cell atom is assigned to a given cell An atom at the center of the cube is a part of An atom at the center of the cube is a part of 8-different cubes touching that point.8-different cubes touching that point. Only corner atom belongs to the cellOnly corner atom belongs to the cell

2

1

8

1

Density of closest packed solidDensity of closest packed solid

# of spheres (atoms) per unit cell = # of spheres (atoms) per unit cell =

Density of closes packed solidDensity of closes packed solid

4)2

16(

8

18 XX

cellunit of volume

atoms (4) of massDensity

4cell atoms/unit ofnumber Net

dcellunit theof Volume

8

24

3

rd

dr

Body centered cubic cellBody centered cubic cell

Atoms contact along a body diagonalAtoms contact along a body diagonal Atoms occupy the corners and one at the centerAtoms occupy the corners and one at the center In a unit cell, 8 atoms occupy the corners plus one in In a unit cell, 8 atoms occupy the corners plus one in

the centerthe center 68% of the space is occupied68% of the space is occupied Available in Group I elements + Ba Available in Group I elements + Ba

Number of atoms assigned to each type of cellNumber of atoms assigned to each type of cell

Simple cubeSimple cube

Body centered cubeBody centered cube

Face centered cubeFace centered cube

cubeper 1atom8

1 X atomscorner 8

atoms 2atomcenter 18

1atomsXcorner 8

atoms 42

1X atoms face 6

8

1 X atomscorner 8

1 atom/unit cell

(8 x 1/8 = 1)

2 atoms/unit cell

(8 x 1/8 + 1 = 2)

4 atoms/unit cell

(8 x 1/8 + 6 x 1/2 = 4)

The highest energy level for most metal atoms

does not contain many electronsThese vacant overlapping orbitals allow outer

electrons to move freely around the entire metalMetallic crystal is an array of positive ions (cations) in a

sea of roaming valence electrons

Electron Sea Model

Metal AlloysMetal Alloys

An alloy is a mixture of elements and has metallic An alloy is a mixture of elements and has metallic propertiesproperties

substitutional alloysubstitutional alloy– host metal atoms are replaced by other metal host metal atoms are replaced by other metal

atoms atoms – host and other metal atoms are similar in sizeshost and other metal atoms are similar in sizes

interstitial alloyinterstitial alloy– metal atoms occupy spaces created between metal atoms occupy spaces created between

host metal atomshost metal atoms– metal atoms have large difference in sizemetal atoms have large difference in size

ExamplesExamples

BrassBrass– substitutionalsubstitutional– 1/3 of Cu atoms 1/3 of Cu atoms

replaced by Zn replaced by Zn SteelSteel

– interstitialinterstitial– Fe with C atoms in Fe with C atoms in

betweenbetween– makes harder and less makes harder and less

malleablemalleable

10.610.6 Molecular solidsMolecular solids

Molecules occupy the corners of the lattices.Molecules occupy the corners of the lattices. Common examples: ice, dry COCommon examples: ice, dry CO22, S, S88, P, P44, I, I22

Different molecules have different forces Different molecules have different forces between them (between them (H-bonds, or dipole-dipole or H-bonds, or dipole-dipole or London forces, or a combination of all these London forces, or a combination of all these forcesforces))

These forces depend on theThese forces depend on the size of the size of the molecule.molecule.

They also depend on theThey also depend on the strength and nature strength and nature of dipole moments.of dipole moments.

Molecular solids with nonpolar molecules Molecular solids with nonpolar molecules (without dipoles): H(without dipoles): H22, CCl, CCl44

Most are gases at 25ºC.Most are gases at 25ºC. The only forces are London Dispersion The only forces are London Dispersion

Forces.Forces. These depend on size of atom.These depend on size of atom. Large molecules (such as ILarge molecules (such as I22 ) can be ) can be

solids even without dipoles.solids even without dipoles.

Molecular solids with polar moleculesMolecular solids with polar molecules (with dipoles): HCl, NH (with dipoles): HCl, NH33

Dipole-dipole forces are generally stronger Dipole-dipole forces are generally stronger than L.D.F.than L.D.F.

Hydrogen bonding is stronger than Dipole-Hydrogen bonding is stronger than Dipole-dipole forces.dipole forces.

No matter how strong the intermolecular No matter how strong the intermolecular force, it is always much, much weaker than force, it is always much, much weaker than the forces in bonds.the forces in bonds.

Stronger forces lead to higher melting and Stronger forces lead to higher melting and freezing pointsfreezing points. .

Water –Molecular solidWater –Molecular solid

Each molecule has two polar O-H bonds.Each molecule has two polar O-H bonds. Each molecule has two lone pair on its Each molecule has two lone pair on its

oxygen.oxygen. Each oxygen can interact with 4 Each oxygen can interact with 4

hydrogen atoms.hydrogen atoms.

HO

H

HO

H

HO

H

10.710.7 Ionic SolidsIonic Solids

• In most of binary ionic compounds, larger ions are arranged in closest packing arrangement, hexagonal (hcp) or cubic (ccp) closest packing

• smaller ions fit in the holes created by the larger ions

• Atoms are actually held together by Atoms are actually held together by electrostatic electrostatic attractionsattractions of opposite charges. of opposite charges.

• They possess They possess huge meltinghuge melting and and boiling boiling points.points.• Atoms are Atoms are locked in latticelocked in lattice so they are hard and so they are hard and

brittle.brittle.• Every electron is accounted for so they are poor Every electron is accounted for so they are poor

conductors-good insulators.conductors-good insulators.

Closest Closest Packing Packing

HolesHoles

The hole is formedby 3 spheres in the Same layer

The hole formed when a sphere occupies a dimple formed by three spheres in an adjacent layer

The holes formedbetween two sets of three spheres in adjoining layers of closest packed structure

Closest packing holesClosest packing holes

Tetrahedral holes: are located above a sphere in the bottom layer

Octahedral holes: are located above a void in the bottom layer

ExamplesExamples

Trigonal holes are so small that they are never Trigonal holes are so small that they are never occupied in binary ionic compoundsoccupied in binary ionic compounds

The type of the hole whether tetrahedral or octahedral The type of the hole whether tetrahedral or octahedral depends mainly ondepends mainly on– Relative sizes of cations and anionsRelative sizes of cations and anions

In ZnS, SIn ZnS, S2-2-, ions are arranged in , ions are arranged in ccpccp with the smaller with the smaller ZnZn2+2+ ions in the tetrahedral holes ions in the tetrahedral holes

In NaCl, ions are arranged in In NaCl, ions are arranged in ccpccp with Na with Na++ ions in the ions in the octahedral holes. octahedral holes.

1010 . .77 Vapor Pressure and changes of stateVapor Pressure and changes of state

vapor-vapor- gas phase above a gas phase above a substance that exists as solid substance that exists as solid or liquid at 25°C and 1 atm.or liquid at 25°C and 1 atm.

Vaporization orVaporization or EvaporationEvaporation - - change from liquid to gas at change from liquid to gas at or below the boiling point . or below the boiling point . ((Endothermic process)Endothermic process)

CondensationCondensation is the change is the change of a gas to a liquid of a gas to a liquid ((Exothermic processExothermic process))

Heat or enthalpy of vaporization, ∆HHeat or enthalpy of vaporization, ∆Hvap vap ::

Energy required to vaporize 1 mole of a liquid at 1 atm

water has a large ∆Hvap (40.7 kJ/mol), (because of hydrogen bonding)

Molar Heats of Vaporization for Selected Liquids

Vapor pressureVapor pressure Initially, liquid in a closed container Initially, liquid in a closed container decreasesdecreases as as

molecules enter gaseous phasemolecules enter gaseous phase When When equilibriumequilibrium is reached, is reached, no more net change no more net change

occursoccurs Rate of condensation and rate of Rate of condensation and rate of

vaporization become equalvaporization become equal Molecules still are changing phase but no Molecules still are changing phase but no

net change (net change (Dynamic equilibriumDynamic equilibrium))

• Gas liquidGas liquid

Vapor pressure is independent of volumeindependent of volume of container as long as some liquid is present (liquid-vapor equilibrium)

Evaporation and condensation

H2O (l) H2O (g)

Rate ofcondensation

Rate ofevaporation=

Dynamic Equilibrium

Equilibrium vapor pressure or vapor pressureEquilibrium vapor pressure or vapor pressure

It is the pressure exerted by the vapor when it is in dynamic equilibrium with a liquid at a constant temperature.

Measurement of Vapor PressureMeasurement of Vapor Pressure

Liquid can be injected under inverted tube

part of the liquid evaporates to the top of tube

Pvap can be determined by height of Hg

PPatmatm = P = Pvapvap + P + PHgHg

The pressure of the vapor phase at equilibrium: Pvap

can be measured when using a simple barometer

Vapor pressure and nature of liquidsVapor pressure and nature of liquids

Vapor pressure depends upon the Vapor pressure depends upon the nature nature of the liquidof the liquid

Liquids with high vapor P (volatile liquids)Liquids with high vapor P (volatile liquids)– evaporate quicklyevaporate quickly– weak intermolecular forcesweak intermolecular forces

Liquids with low vapor PLiquids with low vapor P– Strong London dispersion forcesStrong London dispersion forces (large molar masses) or dipole-dipole (large molar masses) or dipole-dipole

forcesforces

Vapor pressure and temperatureVapor pressure and temperature

Vapor pressure increases with TVapor pressure increases with T More molecules have enough KE to More molecules have enough KE to

overcome intermolecular forcesovercome intermolecular forces

VAPOR PRESSURE CURVES

A liquid boils when its vapor pressure = external pressure.

Temperature EffectTemperature Effect

Kinetic energy

# of

mol

ecu

les T1

Energy needed to overcome intermolecular forces in iquid

Kinetic energy

# of

mol

ecu

les T1T1

T2

At higher temperature more molecules have enough At higher temperature more molecules have enough energy - higher vapor pressure.energy - higher vapor pressure.

Energy needed to overcome intermolecular forces in liquid

Molar heat of vaporization (Hvap) is the energy required to vaporize 1 mole of a liquid.

ln P = -Hvap

RT+ C

Clausius-Clapeyron Equation P = (equilibrium) vapor pressure

T = temperature (K)

R = gas constant (8.314 J/K•mol)

Vapor pressure and Temperature

Mathematical relationshipMathematical relationship

HHvapvap is the heat of vaporization in J/mol is the heat of vaporization in J/mol

12

vap

2T vap,

1Tvap,

T

1-

T

1

R

H =

P

Pln

R = 8.3145 J/K molR = 8.3145 J/K mol..

Vapor Pressure for solidsVapor Pressure for solids

Solids also have vapor Solids also have vapor pressurepressure

SubliminationSublimination– solid gas directlysolid gas directly

– Example: dry ice: COExample: dry ice: CO22

heat of fusion (∆Hheat of fusion (∆Hfusfus))– enthalpy of fusionenthalpy of fusion– enthalpy change at melting enthalpy change at melting

pointpoint

Heating CurveHeating Curve

as energy is added, as energy is added, it is used to it is used to increase the Tincrease the T

when it reaches when it reaches melting point, the melting point, the energy added is energy added is used to change used to change molecules from (s) molecules from (s) to (l) to (l)

plot of plot of T vs. timeT vs. time where energy is added at constant rate where energy is added at constant rate

Changes of stateChanges of state

What happens when a solid is heated?What happens when a solid is heated? The graph of temperature versus heat applied The graph of temperature versus heat applied

is called a is called a heating curveheating curve.. The temperature a solid turns to a liquid is the The temperature a solid turns to a liquid is the

melting point.melting point. The energy required to accomplish this change The energy required to accomplish this change

is called the is called the Heat (or Enthalpy) of Fusion Heat (or Enthalpy) of Fusion HHfusfus

-40

-20

0

20

40

60

80

100

120

140

0 40 120 220 760 800

Heating Curve for Water

IceWater and Ice

Water

Water and Steam Steam

mp

bp

Tem

p

Time (Heat added)

-40

-20

0

20

40

60

80

100

120

140

0 40 120 220 760 800

Heating Curve for Water

Heat of fusion

Heat of vaporization

Slope is Heat Capacity

Time (Heat added)

Tem

p

Hvap=2260 J/g

Hfus=334 J/g

Calculate the enthalpy change upon converting 1 mole of water from ice at -12oC to steam at 115oC.

solid-12oC

solid0oC

liquid0oC

liquid100oC

gas100oC

gas115oC

H1 + H2 + H3 + H4 + H5 = Htotal

Sp. Ht. + Hfusion + Sp. Ht. + HVaporization + Sp. Ht. = Htotal

Specific Heat of ice = 2.09 J/g•K

Hfus=334 J/g

Specific Heat of water = 4.184 J/g•K

Specific Ht. Steam = 1.84 J/g•K

Hvap=2260 J/g

Normal melting PointNormal melting Point

Melting point is determined by the vapor Melting point is determined by the vapor pressure of the solid and the liquid.pressure of the solid and the liquid.

Melting point is the temp at whichMelting point is the temp at which

the vaporthe vapor pressure of the solid = pressure of the solid = vapor pressure of the liquid vapor pressure of the liquid

where the total pressure is 1 atm. where the total pressure is 1 atm.

Solid Water

Liquid Water

Water Vapor Vapor

Apparatus that allows solid and liquid water to interact only through the vapor state

Solid Water

Liquid Water

Water Vapor Vapor

A temp at which the vapor pressure of the solid is higher A temp at which the vapor pressure of the solid is higher than that of the liquid the solid will release molecules to than that of the liquid the solid will release molecules to

achieve equilibriumachieve equilibrium..

Solid Water

Liquid Water

Water Vapor Vapor

While the molecules of water condense to a While the molecules of water condense to a liquid to achieve equilibrium.liquid to achieve equilibrium.

This can only happen if the temperature is above the This can only happen if the temperature is above the melting point since solid is turning to liquid.melting point since solid is turning to liquid.

Solid Water

Liquid Water

Water Vapor Vapor

A temperature at which the vapor pressure of the solid is A temperature at which the vapor pressure of the solid is less than that of the liquid, the liquid will release less than that of the liquid, the liquid will release

molecules to achieve equilibriummolecules to achieve equilibrium..

Solid Water

Liquid Water

Water Vapor Vapor

Solid Water

Liquid Water

Water Vapor Vapor

While the molecules of water condense to a solid.While the molecules of water condense to a solid.

The temperature must be below the melting The temperature must be below the melting point since the liquid is turning to a solid.point since the liquid is turning to a solid.

Solid Water

Liquid Water

Water Vapor Vapor

Temperature at which the vapor pressure of the solid and liquid are equal, Temperature at which the vapor pressure of the solid and liquid are equal, the solid and liquid are vaporizing and condensing at the same rate. the solid and liquid are vaporizing and condensing at the same rate. This is This is the Melting (freezing) point (Temp at which solid and vapor can coexist)the Melting (freezing) point (Temp at which solid and vapor can coexist)

Solid Water

Liquid Water

Water Vapor Vapor

Normal Boiling PointNormal Boiling Point

Temp when vapor Temp when vapor pressure inside the pressure inside the bubbles equals 1 atmbubbles equals 1 atm

If PIf Pvapvap < 1 atm, no bubbles < 1 atm, no bubbles

can form, there is too can form, there is too much pressure on surfacemuch pressure on surface

Normal Boiling PointNormal Boiling Point

Boiling occurs when the vapor pressure of Boiling occurs when the vapor pressure of liquid becomes equal to the external pressure.liquid becomes equal to the external pressure.

Normal boiling pointNormal boiling point is the temperature at is the temperature at which the vapor pressure of a liquid is exactly which the vapor pressure of a liquid is exactly 1 atm pressure.1 atm pressure.

Super heating - Heating above the boiling Super heating - Heating above the boiling point.point.

Supercooling - Cooling below the freezing Supercooling - Cooling below the freezing point.point.

ExceptionsExceptions

supercoolingsupercooling– Material can stay liquid below Material can stay liquid below

melting point because doesn’t melting point because doesn’t achieve level of organization achieve level of organization needed to make solidneeded to make solid

superheatingsuperheating– when heated too quickly, liquid when heated too quickly, liquid

can be raised above boiling pointcan be raised above boiling point– causes “bumping”causes “bumping”

• Changes of state do not always occur exactly at bp or bp

10.9 Phase Diagrams10.9 Phase Diagrams

A plot Representing phases of a substance A plot Representing phases of a substance in a closed system (no material escapes in a closed system (no material escapes into the surroundings and no air is present) into the surroundings and no air is present) as a function of temperature and pressureas a function of temperature and pressure..

Phase changesPhase changes

Gas and liquid areindistinguishable.

Critical temperatureand critical pressure

(all 3 phases exists here)

Phase Diagrams

fusion curve

triple point

critical point

vapor pressure curve

sublimation curve

Critical PointCritical Point

where if the T is increased, vapor can’t where if the T is increased, vapor can’t be be liquefied no matter what P is appliedliquefied no matter what P is applied

at the end of liquid/gas lineat the end of liquid/gas line after this point, only after this point, only one fluid phaseone fluid phase

exists that is neither gas nor liquidexists that is neither gas nor liquid called called supercritical fluidsupercritical fluid

Critical temperatureCritical temperature

Temperature above which the vapor can Temperature above which the vapor can

not be liquefied. not be liquefied. Critical pressure Critical pressure

pressure required to liquefy gas pressure required to liquefy gas ATAT the the

critical temperature. critical temperature. Critical point Critical point

critical temperature and pressure (for critical temperature and pressure (for

water, water, TTcc = 374°C and 218 atm). = 374°C and 218 atm).

Phase diagram Phase diagram for Waterfor Water

Normal mp

No

rmal b

p

Critical tem

pWaterExpands uponfreezing

-ve slope of S/L boundaryline means that mp of icedecreases as the externalP increases

Phase Diagram for H2O

Most Most substances substances have a positive have a positive slope of slope of solid/liquid line solid/liquid line

because because solid is usually solid is usually more dense more dense than liquidthan liquidwater has a water has a negative slopenegative slope

Solid Liquid

Gas

1 Atm

This is the phase diagram for COThis is the phase diagram for CO2 2

The solid is more dense than the liquidThe solid is more dense than the liquid The solid sublimes at 1 atm.The solid sublimes at 1 atm.

Temperature

Pre

ssur

e