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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))
10_208
AttractionRepulsion
(a)
(b)
+– +–
+
–
+
–
–+
+
–
+
–
–
+–
+– +
Electrostatic interaction of two polar molecules.
The polar water molecule and hydrogen bonds among water molecules.
10_210
– 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
10_213
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).).
10_216
= 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.
10_238
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.