liquids & solids chapter 10. heat of fusion/vaporization h 2 o (s) ----> h 2 o (l) h f o =...

Liquids & SolidsLiquids & Solids

Chapter 10

Heat of Fusion/VaporizationHeat of Fusion/Vaporization

HH22OO(s)(s) ----> H ----> H22OO(l) (l) HHffoo = 6.02 kj/mol = 6.02 kj/mol

HH22OO(l)(l) ----> H ----> H22OO(g) (g) HHvvoo = 40.7 kj/mol = 40.7 kj/mol

From the From the HHoo values above, which two states are values above, which two states are most similar?most similar?

How do the attractive forces between the molecules How do the attractive forces between the molecules compare in these two states to the third state? compare in these two states to the third state?

Three States of MatterThree States of Matter

Types of BondingTypes of Bonding

Intramolecular Intramolecular

• within the moleculewithin the molecule

•covalent bondingcovalent bonding

•ionic bondingionic bonding

IntermolecularIntermolecular

•between moleculesbetween molecules

•dipole-dipole forcesdipole-dipole forces

•hydrogen bonding hydrogen bonding

•London Dispersion ForcesLondon Dispersion Forces

When ice changes to liquid and then to vapor, the intramolecular forces (covalent bonds) stay intact, only the weaker hydrogen bonds between molecules weakenand break.

Intermolecular ForcesIntermolecular Forces

Forces between (rather than within) molecules.Forces between (rather than within) molecules.

- dipole-dipole attractiondipole-dipole attraction: molecules with dipoles : molecules with dipoles orient themselves so that “+” and “orient themselves so that “+” and “” ends of ” ends of the dipoles are close to each other. (1 % as strong the dipoles are close to each other. (1 % as strong as covalent or ionic.)as covalent or ionic.)

- hydrogen bondshydrogen bonds: dipole-dipole attraction in : dipole-dipole attraction in which hydrogen is bound to a highly which hydrogen is bound to a highly electronegative atom. (electronegative atom. (F, O, NF, O, N))

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AttractionRepulsion

(a)

(b)

+– +–

+

–

+

–

–+

+

–

+

–

–

+–

+– +

Electrostatic interaction of two polar molecules.

The polar water molecule and hydrogen bonds among water molecules.

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– 100

0

100

– 200

Bo

ilin

g p

oin

t ( °C

)

Period

2 3 4 5

H2 O

Group 6A

Group 7A

Group 5A

Group 4A

HF

NH 3

CH4

SiH4

GeH4

SnH4

HI

SbH3

H2Te

H2SH2Se

HClAsH3

HBr

PH3

The boiling points of the covalent hydrides of the elements in Groups 4A, 5A, 6A, & 7A.

10_211

Atom A Atom B

No polarization

Atom A Atom B

Instantaneous dipole on atom Ainduces a dipole on atom B

Atom A Atom B

(a)

+–

+– +–

No polarization

Instantaneous dipole on molecule Ainduces a dipole on molecule B

(b)

Molecule A Molecule B

Molecule A Molecule B

Molecule A Molecule B

H H H H+ +

+ +

+ +

+ +

+ +

+–+–

+–

H H H H

H H H H

Instantaneous and induced dipole moments between nonpolar molecules -- London Dispersion Forces.

London Dispersion ForcesLondon Dispersion Forces

- relatively weak relatively weak forces that exist among forces that exist among noble gas atoms and nonpolar molecules. noble gas atoms and nonpolar molecules. (Ar, C(Ar, C88HH1818))

- caused by caused by instantaneous dipoleinstantaneous dipole, in which , in which electron distribution becomes asymmetrical.electron distribution becomes asymmetrical.

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

Some Properties of a LiquidSome Properties of a Liquid

Surface TensionSurface Tension: The resistance to an increase in its : The resistance to an increase in its surface area (surface area (polar moleculespolar molecules). ). A sphere has the A sphere has the maximum volume for the minimum surface area.maximum volume for the minimum surface area.

Some Properties of a LiquidSome Properties of a Liquid

Capillary ActionCapillary Action: Spontaneous rising of a liquid : Spontaneous rising of a liquid in a narrow tube. in a narrow tube.

Viscosity: Resistance to flow (molecules with large intermolecular forces).

Some Properties of a LiquidSome Properties of a Liquid

Cohesive forces exist between molecules of a Cohesive forces exist between molecules of a liquid. Adhesive forces exist between the liquid. Adhesive forces exist between the liquid and its container.liquid and its container.

Types of SolidsTypes of Solids

Crystalline SolidsCrystalline Solids: highly regular : highly regular arrangement of their components [arrangement of their components [table salt table salt (NaCl), pyrite (FeS(NaCl), pyrite (FeS22))].].

Amorphous solidsAmorphous solids: considerable disorder in : considerable disorder in their structures (their structures (glassglass).).

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

LatticeLattice: A 3-dimensional system of : A 3-dimensional system of points designating the centers of points designating the centers of components (atoms, ions, or molecules) components (atoms, ions, or molecules) that make up the substance.that make up the substance.

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

Unit CellUnit Cell: The smallest repeating unit of : The smallest repeating unit of the lattice.the lattice.

- simple cubic -- 1 atom/cellsimple cubic -- 1 atom/cell

- body-centered cubic -- 2 atoms/cellbody-centered cubic -- 2 atoms/cell

- face-centered cubic -- 4 atoms/cellface-centered cubic -- 4 atoms/cell

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Simple cubic

Body-centered cubic

Face-centered cubic

(c)

(b)

(a)

Unit cell Lattice Example

Poloniummetal

Uraniummetal

Goldmetal

Three cubic unit cells and the correspondinglattices.

Simple Cubic CellSimple Cubic Cell

• 1 atom per cell1 atom per cell

• side length (dside length (doo) = 2 r) = 2 r

do = 2 r

Body-Body-CenteredCentered Cell Cell• 2 atoms per cell2 atoms per cell

• Body diagonal = dBody diagonal = doo 3 = 4r3 = 4r

• ddoo2 -- diagonal through the 2 -- diagonal through the basebase of cube. of cube.

4r d4r do o

ddoo22

Face-Face-CenteredCentered Cell Cell• 4 atoms per cell4 atoms per cell

• Face diagonal = dFace diagonal = doo 2 = 4r2 = 4r

• ddoo2 -- diagonal through the 2 -- diagonal through the faceface of cube. of cube.

4r d4r do o

ddoo

10_221

(a) (b) (c)

12

atom

18

atom

Face-centered cubic unit cell.

Bragg EquationBragg Equation

Used for analysis of crystal structures and to Used for analysis of crystal structures and to calculate the distance between planes in crystals.calculate the distance between planes in crystals.

nn = 2 = 2dd sin sin

dd = distance between atoms = distance between atoms

nn = an integer = an integer

= wavelength of the x-rays= wavelength of the x-rays

10_214

Waves inphase beforestriking atoms

Waves reinforceeach other, since(d2 - d1) is anintegral number ofX- ray wavelengths.

Waves stillin phase

Waves inphase beforestriking atoms

Waves cancel,because in this case(d2 - d1) is one halfX- ray wavelengths.

No resultantwave

Reinforcement or cancellation of X-rays.

10_215

d

w

y

x z

Incident rays Reflected rays

Reflection of X-rays of wavelength from a pairof atoms in two different layers of a crystal.

Types of Crystalline SolidsTypes of Crystalline Solids

Atomic SolidAtomic Solid: contains atoms at the lattice points : contains atoms at the lattice points ((diamonddiamond).).

Ionic SolidIonic Solid: contains : contains ionsions at the points of the lattice at the points of the lattice that describe the structure of the solid (that describe the structure of the solid (NaClNaCl).).

Molecular SolidMolecular Solid: discrete : discrete covalently bonded covalently bonded molecules at each of its lattice points (molecules at each of its lattice points (sucrose, icesucrose, ice).).

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= Cl

= Na

Sodium chloride

(b)

= H2O= CDiamond Ice

(a) (c)

Three crystalline solids -- a) atomic solid, b) ionicsolid, and c) molecular solid.

Packing in MetalsPacking in Metals

ModelModel: Packing uniform, hard spheres to : Packing uniform, hard spheres to best use available space. This is called best use available space. This is called closest packingclosest packing. Each atom has 12 nearest . Each atom has 12 nearest neighbors.neighbors.

- hexagonal closest packed (“hexagonal closest packed (“abaaba”)”)

- cubic closest packed (“cubic closest packed (“abcabc”)”)

10_217

View from above

View from side(b)(a) (c)

Closest packing arrangement of uniform spheres --aba. This forms hexagonal closest packed -- hcp.

10_218

Atom in third layerlies over atom infirst layer.

Top view

(b)

(a)

(a))

Atoms arranged in aba pattern forming hexagonalclosest packed (hcp) structure -- 2 atoms/cell.

10_220

b

a

b

hcp

1 23

46

5

789

111210

Hexagonal closest packed structure -- centralatom has 12 nearest neighbors.

Face-centered cubic is cubic closest packed (ccp). The spheres are packed in an abcarrangement.

Bonding Models for MetalsBonding Models for MetalsElectron Sea ModelElectron Sea Model: A regular array of metals in a : A regular array of metals in a “sea” of electrons.“sea” of electrons.

Band (Molecular Orbital) ModelBand (Molecular Orbital) Model: Electrons : Electrons assumed to travel around metal crystal in MOs assumed to travel around metal crystal in MOs formed from valence atomic orbitals of metal atoms.formed from valence atomic orbitals of metal atoms.

Conduction Bands: Conduction Bands: closely spaced empty molecular closely spaced empty molecular orbitals allow conductivity of heat and electricity.orbitals allow conductivity of heat and electricity.

10_225

12+ 12+ 12+ 12+ 12+

Empty MOs

Filled MOs

En

erg

y

3p

3s

Magnesiumatoms

2p

2s

1s

Representation of the energy levels (bands) in a magnesium crystal. 1s, 2s, & 2p orbitals are localized, but 3s & 3p orbitals are delocalized to make molecular orbitals.

Metal AlloysMetal Alloys

1.1. Substitutional AlloySubstitutional Alloy: some metal atoms : some metal atoms replacedreplaced by others of similar size. by others of similar size.

brass = Cu/Znbrass = Cu/Zn

Substances that have a mixture of elements and Substances that have a mixture of elements and metallic properties.metallic properties.

Metal AlloysMetal Alloys(continued)(continued)

2.2. Interstitial AlloyInterstitial Alloy: : Interstices (holes) Interstices (holes) in in closest packed metal structure are occupied closest packed metal structure are occupied by by smallsmall atoms. atoms.

steel = iron + carbonsteel = iron + carbon

3.3. Both typesBoth types: : Alloy steels Alloy steels contain a mix of contain a mix of substitutional (Cr, Mo) and interstitial substitutional (Cr, Mo) and interstitial (Carbon) alloys.(Carbon) alloys.

Substitutional Alloy

Interstitial Alloy

Network SolidsNetwork Solids

Composed of strong directional Composed of strong directional covalent covalent bonds bonds that are best viewed as a “giant that are best viewed as a “giant molecule”.molecule”.

- brittlebrittle

- do not conduct heat or electricitydo not conduct heat or electricity

- carbon, silicon-basedcarbon, silicon-based

graphite, diamond, ceramics, glassgraphite, diamond, ceramics, glass

10_229

Diamond(a)

Network solid structure of diamond.

SemiconductorsSemiconductors

- Conductivity is enhanced by Conductivity is enhanced by dopingdoping with group 3a or group 5a elements. with group 3a or group 5a elements.

- n-type semiconductorn-type semiconductor -- doped with atoms having more valence electrons -- doped with atoms having more valence electrons -- Phosphorus.-- Phosphorus.

- p-type semiconductorp-type semiconductor -- doped with atoms having fewer valence electrons -- doped with atoms having fewer valence electrons -- Boron.-- Boron.

- See Figure 10.31 on page 477 in Zumdahl.See Figure 10.31 on page 477 in Zumdahl.

A substance in which some electrons can A substance in which some electrons can cross the band gap.cross the band gap.

Molecular SolidsMolecular Solids

• molecular units at each lattice position.molecular units at each lattice position.

• strong covalent bonding within molecules.strong covalent bonding within molecules.

• relatively weak forces relatively weak forces betweenbetween molecules. molecules.

• London Dispersion Forces -- COLondon Dispersion Forces -- CO22, I, I22, P, P44, & S, & S88..

• Hydrogen Bonding -- HHydrogen Bonding -- H22O, NHO, NH33, & HF., & HF.

Trigonal, Tetrahedral, & Trigonal, Tetrahedral, & Octahedral HolesOctahedral Holes

Trigonal holes -- formed by three spheres in the Trigonal holes -- formed by three spheres in the same layer.same layer.

Tetrahedral holes -- formed when a sphere sits in Tetrahedral holes -- formed when a sphere sits in the dimple of three spheres in an adjacent layer.the dimple of three spheres in an adjacent layer.

Octahedral holes -- formed between two sets of Octahedral holes -- formed between two sets of spheres in adjoining layers of closest packed spheres in adjoining layers of closest packed structures.structures.

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Trigonalhole

Tetrahedralhole

Octahedralhole

(a)

(b)

(c)

Trigonal, Tetrahedral, and Octahedral holes.

Hexagonal & Cubic Closest Hexagonal & Cubic Closest Packed Packed

1 octahedral hole for each atom or ion.1 octahedral hole for each atom or ion.

2 tetrahedral holes for each atom or ion.2 tetrahedral holes for each atom or ion.

Simple cubic and body-centered cubic are not Simple cubic and body-centered cubic are not closest packed structures!closest packed structures!

10_239

(a) (b) (c)ZnS

The location (x) of a tetrahedral hole in the face-centered cubic unit cell. The S2- ions are closest packed with the Zn2+ ions in alternatingtetrahedral holes.

10_240

(a)

(b)

The location (x) of an octahedral hole in the face-centered cubic unit cell. The Cl- ions have a ccp arrangement with the Na+ ions in all the octahedral holes.

Vapor PressureVapor Pressure

. . . is the pressure of the vapor present . . . is the pressure of the vapor present at at equilibriumequilibrium..

. . . is determined principally by the size of . . . is determined principally by the size of the intermolecular forces in the liquid.the intermolecular forces in the liquid.

. . . increases significantly with temperature.. . . increases significantly with temperature.

Volatile liquids Volatile liquids have high vapor pressures.have high vapor pressures.

Vapor PressureVapor Pressure

Low boiling pointLow boiling point

• high vapor pressure. high vapor pressure.

• weak intermolecular forces.weak intermolecular forces.

Low vapor pressureLow vapor pressure

• high molar masses.high molar masses.

• strong intermolecular forces.strong intermolecular forces.

10_245

T1

Kinetic energy(a)

Num

ber

of m

ole

cule

sw

ith a

giv

en e

nerg

y Energy neededto overcomeintermolecular forces in liquid

T2

Kinetic energy(b)

Num

ber

of m

ole

cule

sw

ith a

giv

en e

nerg

y Energy neededto overcomeintermolecular forces in liquid

Boltzman Distribution -- number of molecules ina liquid with a given energy versus kinetic energy at two different temperatures.

Natural Log of Vapor Pressure Versus Natural Log of Vapor Pressure Versus Reciprocal Kelvin TemperatureReciprocal Kelvin Temperature

y = m x + by = m x + b

Slope = If the slope is known, Slope = If the slope is known, then then H can be calculated.H can be calculated.

CT

1

R

H)(Pln vapvap

R

Hvap

Clausius-Clayperon EquationClausius-Clayperon Equation

Temperatures must be expressed in Kelvin.Temperatures must be expressed in Kelvin.

See Example 10.6 on page 488 in Zumdahl.See Example 10.6 on page 488 in Zumdahl.

ln

211

2

T

1

T

1

R

H

P

Pln

SublimationSublimation

•Change of a solid Change of a solid directly to a vapor directly to a vapor without passing through without passing through the liquid state. the liquid state.

•IodineIodine

•Dry IceDry Ice

•Moth BallsMoth Balls

Melting PointMelting Point

Molecules break loose from lattice points and Molecules break loose from lattice points and solid changes to liquid. (Temperature is constant solid changes to liquid. (Temperature is constant as melting occurs.)as melting occurs.)

vapor pressure of solid = vapor pressure of liquidvapor pressure of solid = vapor pressure of liquid

Boiling PointBoiling Point

Constant temperature when added energy is used Constant temperature when added energy is used to vaporize the liquid.to vaporize the liquid.

vapor pressure of liquid = pressure ofvapor pressure of liquid = pressure of surrounding surrounding

atmosphereatmosphere

Phase DiagramPhase Diagram

Represents phases as a function of temperature and Represents phases as a function of temperature and pressure.pressure.

critical temperaturecritical temperature: temperature above which the : temperature above which the vapor can not be liquefied.vapor can not be liquefied.

critical pressurecritical pressure: pressure required to liquefy : pressure required to liquefy ATAT the the critical temperature.critical temperature.

critical pointcritical point: critical temperature and pressure (for : critical temperature and pressure (for water, water, TTcc = 374°C and 218 atm). = 374°C and 218 atm).

10_247

Te

mp

era

ture

(°C

)

Time

– 20

0

20

40

60

80

100

120

140Steam

Water and steam

Water

Ice andwater

Ice

Heating curve for water.H = (ms t)ice + m Hf + (ms t) water + m Hv + (mst)steam

E = KE & PE + PE + KE & PE + PE + PE & KE

10_249

Water vapor

Solidwater

Liquidwater

Solid and liquid water interact only through the vapor state.

10_252

Pc = 218

1.00P3 = 0.0060

Tm T3 Tb

0 0.0098 100 374

Solid Liquid

Gas

Temperature ( ° C)

Pre

ssur

e (a

tm)

Triplepoint

Criticalpoint

Tc

Phase diagram for water -- Tm is the regular meltingpoint. The solid/liquid line has a negative slope.

10_255

Pc =

72.8

1.00

P3 =

5.1

Tm T3 Tc

Solid

Liquid

GasTriplepoint

Temperature (°C)

– 78 – 56.6 31

Pre

ssur

e (a

tm)

Criticalpoint

Phase diagram for carbon dioxide -- the solid/liquid line has a positive slope.

10_256

Pre

ssur

e (m

m H

g)

Temperature (°C)

Rhombic

Liquid

Mon

oclin

ic

(119°C, 0.0027 mm Hg)

(96°C, 0.0043 mmHg)

Vapor

Phase diagram for sulfur -- note the two differentsolid forms of rhombic and monoclinic sulfur.

10_257

Diamond

Graphite

Liquid

Vapor

107

109

1011

0 2000 4000 6000

Temperature (K)

Pre

ssur

e (P

a)

Phase diagram for carbon -- note the two solid forms of diamond and graphite.