1 CHAPTER 11 Intermolecular Forces, Liquids and Solids.

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CHAPTER 11CHAPTER 11

Intermolecular Forces, Intermolecular Forces, Liquids and SolidsLiquids and Solids

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Description of Liquids & SolidsDescription of Liquids & Solids• Solids & liquids are Solids & liquids are condensed statescondensed states

• atoms, ions, molecules are close to one anotheratoms, ions, molecules are close to one another• highly incompressiblehighly incompressible• Solid molecules are packed closely together. The molecules are Solid molecules are packed closely together. The molecules are

so rigidly packed that they cannot easily slide past each other.so rigidly packed that they cannot easily slide past each other.

• Liquids & gases are Liquids & gases are fluidsfluids• easily floweasily flow• Liquid molecules are held closer together than gas molecules, Liquid molecules are held closer together than gas molecules,

but not so rigidly that the molecules cannot slide past each but not so rigidly that the molecules cannot slide past each other.other.

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Description of Liquids & Solids

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Converting a gas into a liquid or solid requires Converting a gas into a liquid or solid requires the molecules to get closer to each other:the molecules to get closer to each other: cool or compress.cool or compress.

Converting a solid into a liquid or gas requires Converting a solid into a liquid or gas requires the molecules to move further apart: the molecules to move further apart: heat or reduce pressure.heat or reduce pressure.

The forces holding solids and liquids together The forces holding solids and liquids together are called are called intermolecular forces.intermolecular forces.

Description of Liquids & Solids

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Kinetic-Molecular Description of Kinetic-Molecular Description of Liquids & SolidsLiquids & Solids

strengths of interactionsstrengths of interactions among particles & among particles &

degree of orderingdegree of ordering of particles of particles

Gases< Liquids < SolidsGases< Liquids < Solids

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Intermolecular Attractions

The covalent bond holding a molecule together is an The covalent bond holding a molecule together is an intramolecular forces.intramolecular forces.

The attraction between molecules is an intermolecular The attraction between molecules is an intermolecular force.force.

Intermolecular forces are much weaker than intramolecular Intermolecular forces are much weaker than intramolecular forces (e.g. 16 kJ/mol vs. 431 kJ/mol for HCl).forces (e.g. 16 kJ/mol vs. 431 kJ/mol for HCl).

When a substance melts or boils the intermolecular forces When a substance melts or boils the intermolecular forces are broken (not the covalent bonds).are broken (not the covalent bonds).

When a substance condenses intermolecular forces are When a substance condenses intermolecular forces are

formedformed..

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Intermolecular AttractionsIon-Dipole ForcesIon-Dipole Forces Ion-dipole forces exist between an ion and Ion-dipole forces exist between an ion and

a the partial charge on the end of a polar a the partial charge on the end of a polar molecule.molecule.

Positive ions are attracted to the negative Positive ions are attracted to the negative end of the dipole (and vice versa)end of the dipole (and vice versa)

Magnitude of the attraction increases with Magnitude of the attraction increases with increasing ionic charge or dipole moment.increasing ionic charge or dipole moment.

Important when ionic compound are Important when ionic compound are dissolved in water.dissolved in water.

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Intermolecular AttractionsDipole-Dipole ForcesDipole-Dipole Forces Dipole-dipole forces exist between neutral Dipole-dipole forces exist between neutral

polar molecules.polar molecules. Polar molecules need to be close together.Polar molecules need to be close together. Weaker than ion-dipole forces:Weaker than ion-dipole forces:

QQ11 and and QQ22 are are partialpartial charges. charges.

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d

QQkF

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Dipole-Dipole ForcesDipole-Dipole Forces There is a mix of attractive and There is a mix of attractive and

repulsive dipole-dipole forces repulsive dipole-dipole forces as the molecules tumble.as the molecules tumble.

If two molecules have about If two molecules have about the same mass and size, then the same mass and size, then dipole-dipole forces increase dipole-dipole forces increase with increasing polarity.with increasing polarity.

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Intermolecular AttractionsIntermolecular Attractions

Dipole-dipole interactionsDipole-dipole interactions consider NHconsider NH33 a very polar molecule a very polar molecule

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London Dispersion Forces Weakest of all intermolecular forces.Weakest of all intermolecular forces. It is possible for two adjacent neutral molecules to It is possible for two adjacent neutral molecules to

affect each other.affect each other. The nucleus of one molecule (or atom) attracts the The nucleus of one molecule (or atom) attracts the

electrons of the adjacent molecule (or atom).electrons of the adjacent molecule (or atom). For an instant, the electron clouds become For an instant, the electron clouds become

distorted.distorted. In that instant a dipole is formed (called an In that instant a dipole is formed (called an

instantaneous dipole).instantaneous dipole).

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Intermolecular AttractionsDispersion Forces

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Polarizability is the ease with which an Polarizability is the ease with which an electron cloud can be deformed.electron cloud can be deformed.

The larger the molecule (the greater the The larger the molecule (the greater the number of electrons) the more number of electrons) the more polarizable.polarizable.


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Intermolecular AttractionsDispersion Forces London dispersion forces depend on the London dispersion forces depend on the

shape of the molecule.shape of the molecule. The greater the surface area available for The greater the surface area available for

contact, the greater the dispersion forces.contact, the greater the dispersion forces. London dispersion forces between London dispersion forces between

spherical molecules are smaller than spherical molecules are smaller than between sausage-like molecules.between sausage-like molecules.

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Hydrogen bondingHydrogen bonding consider Hconsider H22OO

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Hydrogen BondingHydrogen Bonding Special case of dipole-dipole forces.Special case of dipole-dipole forces. By experiments: boiling points of By experiments: boiling points of

compounds with H-F, H-O, and H-N compounds with H-F, H-O, and H-N bonds are abnormally high.bonds are abnormally high.

Intermolecular forces are abnormally Intermolecular forces are abnormally strong.strong.


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Hydrogen BondingHydrogen Bonding H-bonding requires H bonded to an H-bonding requires H bonded to an

electronegative element (most important electronegative element (most important for compounds of F, O, and N).for compounds of F, O, and N). Electrons in the H-X (X = electronegative Electrons in the H-X (X = electronegative

element) lie much closer to X than H.element) lie much closer to X than H. H has only one electron, so in the H-X H has only one electron, so in the H-X

bond, the bond, the + H presents an almost bare + H presents an almost bare proton to the proton to the - X.- X.

Therefore, H-bonds are strong.Therefore, H-bonds are strong.


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Hydrogen BondingHydrogen BondingIntermolecular Attractions

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Hydrogen BondingHydrogen Bonding Ice FloatingIce Floating

• Solids are usually more closely packed than liquids;Solids are usually more closely packed than liquids;• therefore, solids are more dense than liquids.therefore, solids are more dense than liquids.• Ice is ordered with an open structure to optimize H-bonding.Ice is ordered with an open structure to optimize H-bonding.• Therefore, ice is less dense than water.Therefore, ice is less dense than water.• In water the H-O bond length is 1.0 Å.In water the H-O bond length is 1.0 Å.• The O…H hydrogen bond length is 1.8 Å.The O…H hydrogen bond length is 1.8 Å.• Ice has waters arranged in an open, regular hexagon.Ice has waters arranged in an open, regular hexagon.• Each Each + H points towards a lone pair on O.+ H points towards a lone pair on O.• Ice floats, so it forms an insulating layer on top of lakes, Ice floats, so it forms an insulating layer on top of lakes,

rivers, etc. Therefore, aquatic life can survive in winter.rivers, etc. Therefore, aquatic life can survive in winter.


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Hydrogen BondingHydrogen Bonding Hydrogen bonds Hydrogen bonds

are responsible for:are responsible for: Protein StructureProtein Structure

• Protein folding is a Protein folding is a consequence of H-consequence of H-bonding.bonding.

• DNA Transport of DNA Transport of Genetic InformationGenetic Information


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Comparing Intermolecular Attractions

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Intermolecular interactions determine: Intermolecular interactions determine: melting & boiling points of ionic compoundsmelting & boiling points of ionic compounds the solubility of ionic compoundsthe solubility of ionic compounds

Arrange the following ionic compounds Arrange the following ionic compounds in the expected order of increasing in the expected order of increasing melting and boiling points.melting and boiling points.

NaF, CaO, CaFNaF, CaO, CaF22

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Intermolecular Attractions and Intermolecular Attractions and Phase ChangesPhase Changes

Na F Ca F Ca O+ - 2+2

2+ 2-

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Intermolecular Attractions and Intermolecular Attractions and Phase ChangesPhase Changes

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Vapor PressureVapor Pressure

pressure exerted by a liquid’s vapor on its pressure exerted by a liquid’s vapor on its surface at equilibriumsurface at equilibrium

Vap. Press. (torr) for 3 LiquidsVap. Press. (torr) for 3 Liquids Norm. Norm. B.P.B.P.

00ooCC 20 20ooCC 30 30ooCC diethyl etherdiethyl ether 185 185 442 442 647 647 3636ooCC ethanolethanol 12 12 44 44 74 74 7878ooCC waterwater 5 5 18 18 32 32 100100ooCC

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Some of the molecules on the surface of a liquid Some of the molecules on the surface of a liquid have enough energy to escape the attraction of have enough energy to escape the attraction of the bulk liquid.the bulk liquid.

These molecules move into the gas phase.These molecules move into the gas phase. As the number of molecules in the gas phase As the number of molecules in the gas phase

increases, some of the gas phase molecules increases, some of the gas phase molecules strike the surface and return to the liquid.strike the surface and return to the liquid.

After some time the pressure of the gas will be After some time the pressure of the gas will be constant at the vapor pressure.constant at the vapor pressure.

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Dynamic Equilibrium: the Dynamic Equilibrium: the point when as many point when as many molecules escape the molecules escape the surface as strike the surface as strike the surface.surface.

Vapor pressure is the Vapor pressure is the pressure exerted when the pressure exerted when the liquid and vapor are in liquid and vapor are in dynamic equilibrium.dynamic equilibrium.


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If equilibrium is never established then If equilibrium is never established then the liquid evaporates.the liquid evaporates.

Volatile substances evaporate rapidly.Volatile substances evaporate rapidly. The higher the temperature, the higher The higher the temperature, the higher

the average kinetic energy, the faster the the average kinetic energy, the faster the liquid evaporates.liquid evaporates.


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Liquids boil when the external pressure equals Liquids boil when the external pressure equals the vapor pressure.the vapor pressure.

Temperature of boiling point increases as Temperature of boiling point increases as pressure increases.pressure increases.

Two ways to get a liquid to boil: increase Two ways to get a liquid to boil: increase temperature or decrease pressure.temperature or decrease pressure. Pressure cookers operate at high pressure. At high Pressure cookers operate at high pressure. At high

pressure the boiling point of water is higher than at 1 pressure the boiling point of water is higher than at 1 atm. Therefore, there is a higher temperature at atm. Therefore, there is a higher temperature at which the food is cooked, reducing the cooking time which the food is cooked, reducing the cooking time required.required.


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Boiling PointsBoiling Points

Boiling point is the temperature at which Boiling point is the temperature at which the liquid’s vapor pressure is equal to the the liquid’s vapor pressure is equal to the applied pressureapplied pressure normal boiling point is boiling point @ 1 atmnormal boiling point is boiling point @ 1 atm

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DistillationDistillation

Process in which a mixture or solution is Process in which a mixture or solution is separated into its components on the separated into its components on the basis of the differences in boiling points of basis of the differences in boiling points of the componentsthe components Distillation is another vapor pressure Distillation is another vapor pressure

phenomenon.phenomenon.

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Surface molecules are only attracted Surface molecules are only attracted inwards towards the bulk molecules.inwards towards the bulk molecules.

SublimationSublimation: solid : solid gas. gas. VaporizationVaporization: liquid : liquid gas. gas. Melting Melting or or fusionfusion: solid : solid liquid. liquid. DepositionDeposition: gas : gas solid. solid. CondensationCondensation: gas : gas liquid. liquid. FreezingFreezing: liquid : liquid solid. solid.

Phase ChangesPhase Changes

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SublimationSublimation: : HHsubsub > 0 (endothermic). > 0 (endothermic).

VaporizationVaporization: : HHvapvap > 0 (endothermic). > 0 (endothermic).

Melting Melting or or FusionFusion: : HHfusfus > 0 (endothermic). > 0 (endothermic).

DepositionDeposition: : HHdepdep < 0 (exothermic). < 0 (exothermic).

CondensationCondensation: : HHconcon < 0 (exothermic). < 0 (exothermic).

FreezingFreezing: : HHfrefre < 0 (exothermic). < 0 (exothermic).

Generally heat of fusion (enthalpy of fusion) is Generally heat of fusion (enthalpy of fusion) is less than heat of vaporization:less than heat of vaporization: it takes more energy to completely separate it takes more energy to completely separate

molecules, than partially separate them.molecules, than partially separate them.


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All phase changes are possible under the right All phase changes are possible under the right conditions (e.g. water sublimes when snow conditions (e.g. water sublimes when snow disappears without forming puddles).disappears without forming puddles).

The sequenceThe sequence

heat solid heat solid melt melt heat liquid heat liquid boil boil heat gas heat gas

is is endothermicendothermic.. The sequence The sequence

cool gas cool gas condense condense cool liquid cool liquid freeze freeze

cool solidcool solid

is is exothermicexothermic..


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Plot of temperature change versus heat added Plot of temperature change versus heat added is a heating curve.is a heating curve.

During a phase change, adding heat During a phase change, adding heat causes no temperature change.causes no temperature change. These points are used to calculate These points are used to calculate HHfusfus and and HHvapvap..

SupercoolingSupercooling: When a liquid is cooled : When a liquid is cooled below its melting point and it still remains below its melting point and it still remains a liquid.a liquid.

Achieved by keeping the temperature low and Achieved by keeping the temperature low and increasing kinetic energy to break increasing kinetic energy to break intermolecular forces.intermolecular forces.


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Phase Changes and Heating Phase Changes and Heating CurvesCurves

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Gases liquefied by increasing pressure at Gases liquefied by increasing pressure at some temperature.some temperature.

Critical temperatureCritical temperature: the maximum : the maximum temperature a liquid can exist.temperature a liquid can exist.

Critical pressureCritical pressure: pressure required for : pressure required for liquefaction at the critical temperature.liquefaction at the critical temperature.

Critical Temperature and Critical Temperature and PressurePressure

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Phase Diagrams (P vs T)Phase Diagrams (P vs T)

convenient way to display all of the different phases of a substance convenient way to display all of the different phases of a substance phase phase

diagram for diagram for waterwater

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Phase Diagrams (P vs T)Phase Diagrams (P vs T)

phase phase diagram diagram for for carbon carbon dioxidedioxide

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Structures of SolidsStructures of Solids

Solids have maximum intermolecular forces.Solids have maximum intermolecular forces. Molecular crystals are formed by close packing Molecular crystals are formed by close packing

of the molecules (model by packing spheres).of the molecules (model by packing spheres). We rationalize maximum intermolecular force in We rationalize maximum intermolecular force in

a crystal by the close packing of spheres.a crystal by the close packing of spheres. When spheres are packed as closely as When spheres are packed as closely as

possible, there are small spaces between possible, there are small spaces between adjacent spheres.adjacent spheres.

The spaces are called interstitial holes.The spaces are called interstitial holes.

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A crystal is built up by placing close packed A crystal is built up by placing close packed layers of spheres on top of each other.layers of spheres on top of each other.

There is only one place for the second layer of There is only one place for the second layer of spheres.spheres.

There are two choices for the third layer of There are two choices for the third layer of spheres:spheres: Third layer eclipses the first (ABAB arrangement). Third layer eclipses the first (ABAB arrangement).

This is called hexagonal close packing (hcp);This is called hexagonal close packing (hcp); Third layer is in a different position relative to the Third layer is in a different position relative to the

first (ABCABC arrangement). This is called cubic first (ABCABC arrangement). This is called cubic close packing (ccp).close packing (ccp).

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Close Packing of SpheresClose Packing of Spheres Each sphere is surrounded by 12 other spheres Each sphere is surrounded by 12 other spheres

(6 in one plane, 3 above and 3 below).(6 in one plane, 3 above and 3 below). Coordination number: the number of spheres Coordination number: the number of spheres

directly surrounding a central sphere.directly surrounding a central sphere. Hexagonal and cubic close packing are different Hexagonal and cubic close packing are different

from the cubic unit cells.from the cubic unit cells. If unequally sized spheres are used, the smaller If unequally sized spheres are used, the smaller

spheres are placed in the interstitial holes.spheres are placed in the interstitial holes.


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X-Ray DiffractionX-Ray Diffraction When waves are passed through a narrow slit When waves are passed through a narrow slit

they are diffracted.they are diffracted. When waves are passed through a diffraction When waves are passed through a diffraction

grating (many narrow slits in parallel) they grating (many narrow slits in parallel) they interact to form a diffraction pattern (areas of interact to form a diffraction pattern (areas of light and dark bands).light and dark bands).

Efficient diffraction occurs when the wavelength Efficient diffraction occurs when the wavelength of light is close to the size of the slits.of light is close to the size of the slits.

The spacing between layers in a crystal is 2 - 20 The spacing between layers in a crystal is 2 - 20 Å, which is the wavelength range for X-rays.Å, which is the wavelength range for X-rays.


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X-ray diffraction (X-ray crystallography):X-ray diffraction (X-ray crystallography): X-rays are passed through the crystal and are X-rays are passed through the crystal and are

detected on a photographic plate.detected on a photographic plate. The photographic plate has one bright spot at the The photographic plate has one bright spot at the

center (incident beam) as well as a diffraction center (incident beam) as well as a diffraction pattern.pattern.

Each close packing arrangement produces a Each close packing arrangement produces a different diffraction pattern.different diffraction pattern.

Knowing the diffraction pattern, we can calculate the Knowing the diffraction pattern, we can calculate the positions of the atoms required to produce that positions of the atoms required to produce that pattern.pattern.

We calculate the crystal structure based on a We calculate the crystal structure based on a knowledge of the diffraction pattern.knowledge of the diffraction pattern.


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X-Ray DiffractionX-Ray Diffraction

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Unit CellsUnit Cells Crystalline solidCrystalline solid: well-ordered, definite : well-ordered, definite

arrangements of molecules, atoms or ions. arrangements of molecules, atoms or ions. Crystals have an ordered, repeated structure.Crystals have an ordered, repeated structure. The smallest repeating unit in a crystal is a unit The smallest repeating unit in a crystal is a unit

cell.cell. Unit cell is the smallest unit with all the symmetry Unit cell is the smallest unit with all the symmetry

of the entire crystal.of the entire crystal. Three-dimensional stacking of unit cells is the Three-dimensional stacking of unit cells is the

crystal latticecrystal lattice..


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Unit CellsUnit CellsStructures of SolidsStructures of Solids

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Three common types of unit cell.Three common types of unit cell. Primitive cubicPrimitive cubic, atoms at the corners of a simple , atoms at the corners of a simple

cube,cube,• each atom shared by 8 unit cells;each atom shared by 8 unit cells;

Body-centered cubicBody-centered cubic (bcc), atoms at the corners of (bcc), atoms at the corners of a cube plus one in the center of the body of the a cube plus one in the center of the body of the cube,cube,

• corner atoms shared by 8 unit cells, center atom corner atoms shared by 8 unit cells, center atom completely enclosed in one unit cell;completely enclosed in one unit cell;

Face-centered cubicFace-centered cubic (fcc), atoms at the corners of a (fcc), atoms at the corners of a cube plus one atom in the center of each face of the cube plus one atom in the center of each face of the cube,cube,

• corner atoms shared by 8 unit cells, face atoms shared by corner atoms shared by 8 unit cells, face atoms shared by 2 unit cells.2 unit cells.


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Simple Simple cubiccubic


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Structure of CrystalsStructure of Crystals Simple cubicSimple cubic

each particle at a corner is shared by 8 unit each particle at a corner is shared by 8 unit cellscells

1 unit cell contains 8(1/8) = 1 particle1 unit cell contains 8(1/8) = 1 particle

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Structure of CrystalsStructure of Crystals

Body centered cubic (bcc)Body centered cubic (bcc) 8 corners + 1 particle in center of cell8 corners + 1 particle in center of cell 1 unit cell contains 8(1/8) + 1 = 2 particles1 unit cell contains 8(1/8) + 1 = 2 particles

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Face Face centered centered cubic (fcc)cubic (fcc)

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Face centered cubic (fcc)Face centered cubic (fcc) 8 corners + 6 faces8 corners + 6 faces 1 unit cell contains 8(1/8) + 6(1/2) = 4 1 unit cell contains 8(1/8) + 6(1/2) = 4

particlesparticles

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Molecular (formed from molecules) - usually soft Molecular (formed from molecules) - usually soft with low melting points and poor conductivity.with low melting points and poor conductivity.

Covalent network (formed from atoms) - very Covalent network (formed from atoms) - very hard with very high melting points and poor hard with very high melting points and poor conductivity.conductivity.

Ions (formed form ions) - hard, brittle, high Ions (formed form ions) - hard, brittle, high melting points and poor conductivity.melting points and poor conductivity.

Metallic (formed from metal atoms) - soft or hard, Metallic (formed from metal atoms) - soft or hard, high melting points, good conductivity, high melting points, good conductivity, malleable and ductile.malleable and ductile.

Bonding in SolidsBonding in Solids

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Intermolecular forces: dipole-dipole, Intermolecular forces: dipole-dipole, London dispersion and H-bonds.London dispersion and H-bonds.

Weak intermolecular forces give rise to Weak intermolecular forces give rise to low melting points.low melting points.

Room temperature gases and liquids Room temperature gases and liquids usually form molecular solids and low usually form molecular solids and low temperature.temperature.

Efficient packing of molecules is important Efficient packing of molecules is important (since they are not regular spheres).(since they are not regular spheres).

Molecular SolidsMolecular Solids

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Molecular SolidsMolecular Solids

molecules occupy unit cellsmolecules occupy unit cells low melting points,volatile & insulatorslow melting points,volatile & insulators examples:examples:

• water, sugar, carbon dioxide, benzenewater, sugar, carbon dioxide, benzene

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Covalently Bonded SolidsCovalently Bonded Solids

Intermolecular forces: dipole-dipole, London Intermolecular forces: dipole-dipole, London dispersion and H-bonds.dispersion and H-bonds.

Atoms held together in large networks.Atoms held together in large networks. Examples: diamond, graphite, quartz (SiOExamples: diamond, graphite, quartz (SiO22), silicon ), silicon

carbide (SiC), and boron nitride (BN).carbide (SiC), and boron nitride (BN). In diamond:In diamond:

each C atom has a coordination number of 4;each C atom has a coordination number of 4; each C atom is tetrahedral;each C atom is tetrahedral; there is a three-dimensional array of atoms.there is a three-dimensional array of atoms. Diamond is hard, and has a high melting point (3550 Diamond is hard, and has a high melting point (3550

C).C).

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In graphiteIn graphite each C atom is arranged in a planar hexagonal ring;each C atom is arranged in a planar hexagonal ring; layers of interconnected rings are placed on top of layers of interconnected rings are placed on top of

each other;each other; the distance between C atoms is close to benzene the distance between C atoms is close to benzene

(1.42 Å vs. 1.395 Å in benzene);(1.42 Å vs. 1.395 Å in benzene); the distance between layers is large (3.41 Å);the distance between layers is large (3.41 Å); electrons move in delocalized orbitals (good electrons move in delocalized orbitals (good

conductor).conductor).


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Ions (spherical) held together by electrostatic Ions (spherical) held together by electrostatic forces of attraction:forces of attraction:

The higher the charge (The higher the charge (QQ) and smaller the distance ) and smaller the distance ((dd) between ions, the stronger the ionic bond.) between ions, the stronger the ionic bond.

There are some simple classifications for ionic There are some simple classifications for ionic lattice types:lattice types:

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d

QQkF

Ionic SolidsIonic Solids

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NaCl StructureNaCl Structure• Each ion has a coordination number of 6.Each ion has a coordination number of 6.• Face-centered cubic lattice.Face-centered cubic lattice.• Cation to anion ratio is 1:1.Cation to anion ratio is 1:1.• Examples: LiF, KCl, AgCl and CaO.Examples: LiF, KCl, AgCl and CaO.

CsCl StructureCsCl Structure• CsCs++ has a coordination number of 8. has a coordination number of 8.• Different from the NaCl structure (CsDifferent from the NaCl structure (Cs++ is larger is larger

than Nathan Na++).).• Cation to anion ratio is 1:1.Cation to anion ratio is 1:1.


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Crystal Structure of Sodium ChlorideCrystal Structure of Sodium Chloride Face-centered cubic lattice.Face-centered cubic lattice. Two equivalent ways of defining unit cell:Two equivalent ways of defining unit cell:

ClCl-- (larger) ions at the corners of the cell, or (larger) ions at the corners of the cell, or NaNa++ (smaller) ions at the corners of the cell. (smaller) ions at the corners of the cell.

The cation to anion ratio in a unit cell is the The cation to anion ratio in a unit cell is the same for the crystal. In NaCl each unit cell same for the crystal. In NaCl each unit cell contains same number of Nacontains same number of Na++ and Cl and Cl-- ions. ions.

Note the unit cell for CaClNote the unit cell for CaCl22 needs twice as needs twice as

many Clmany Cl-- ions as Ca ions as Ca2+ 2+ ions.ions.


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Metallic solids have metal atoms in hcp, Metallic solids have metal atoms in hcp, fcc or bcc arrangements.fcc or bcc arrangements.

Coordination number for each atom is Coordination number for each atom is either 8 or 12.either 8 or 12.

Problem: the bonding is too strong for Problem: the bonding is too strong for London dispersion and there are not London dispersion and there are not enough electrons for covalent bonds.enough electrons for covalent bonds.

Metallic SolidsMetallic Solids

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Resolution: the metal nuclei float in a sea of Resolution: the metal nuclei float in a sea of electrons.electrons.

Metals conduct because the electrons are Metals conduct because the electrons are delocalized and are mobile.delocalized and are mobile.

positively charged nuclei surrounded by a sea positively charged nuclei surrounded by a sea of electronsof electrons positive ions occupy lattice positionspositive ions occupy lattice positions

examples:examples:• Na, Li, Au, Ag, ……..Na, Li, Au, Ag, ……..

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Variations in Melting PointsVariations in Melting Points Molecular SolidsMolecular Solids

CompoundCompound Melting Point (Melting Point (ooC)C)

iceice 0 0

ammoniaammonia -77.7-77.7

benzene, Cbenzene, C66HH66 5.5 5.5

napthalene, Cnapthalene, C1010HH88 80.680.6

benzoic acid, Cbenzoic acid, C66HH55COCO22HH 122.4122.4

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Covalent SolidsCovalent Solids

SubstanceSubstance

sand, SiOsand, SiO22

carborundum, SiCcarborundum, SiC

diamonddiamond

graphitegraphite

Melting Point (Melting Point (ooC)C)

17131713

~2700~2700

>3550>3550

3652-36973652-3697

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Bonding in SolidsBonding in Solids Ionic SolidsIonic SolidsCompoundCompoundLiFLiFLiClLiClLiBrLiBrLiILiICaFCaF22

CaClCaCl22CaBrCaBr22

CaICaI22

Melting Point (Melting Point (ooC)C) 842842 614614 547547 45045013601360 772772 730730 740740

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MetalMetal

NaNa

PbPb

AlAl

CuCu

FeFe

WW

Melting Point (Melting Point (ooC)C)

9898

328328

660660

10831083

15351535

34103410

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Band Theory of MetalsBand Theory of Metals Na’s 3s orbitals can interact to produce Na’s 3s orbitals can interact to produce

overlapping orbitalsoverlapping orbitals

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Band Theory of MetalsBand Theory of Metals

Can also overlap with unfilled 3p orbitalsCan also overlap with unfilled 3p orbitals

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Band Theory of MetalsBand Theory of Metals Insulators have a large gap - Insulators have a large gap - forbidden forbidden

zonezone Semiconductors have a small gapSemiconductors have a small gap

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Synthesis QuestionSynthesis Question

Maxwell House Coffee Company Maxwell House Coffee Company decaffeinates its coffee beans using an decaffeinates its coffee beans using an extractor that is 7.0 feet in diameter and extractor that is 7.0 feet in diameter and 70.0 feet long. Supercritical carbon 70.0 feet long. Supercritical carbon dioxide at a pressure of 300.0 atm and dioxide at a pressure of 300.0 atm and temperature of 100.0temperature of 100.000C is passed through C is passed through the stainless steel extractor. The the stainless steel extractor. The extraction vessel contains 100,000 extraction vessel contains 100,000 pounds of coffee beans soaked in water pounds of coffee beans soaked in water until they have a water content of 50%. until they have a water content of 50%.

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This process removes 90% of the caffeine This process removes 90% of the caffeine in a single pass of the beans through the in a single pass of the beans through the extractor. Carbon dioxide that has passed extractor. Carbon dioxide that has passed over the coffee is then directed into a over the coffee is then directed into a waterwater column that washes the caffeine column that washes the caffeine from the supercritical COfrom the supercritical CO22. How many . How many

moles of carbon dioxide are present in the moles of carbon dioxide are present in the extractor?extractor?

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L 107.633

mL) L/1000 )(1mL/cm )(1cm10(7.633

(2134cm)06.7cm)(3.1416)(1hr vesselof Volume

cm 2134 cm/ft) ft)(30.48 (70.0 vesselofLength

cm 106.7 cm/2 213.4 vesselof Radius

cm 213.4cm/ft) ft)(30.48 (7.0 vesselofDiameter

4

337

22

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2

K molatm L

4

CO of mol 748,000n

K 3730.08206

L 107.633atm 300RT

PVn

nRTPV

8686

Group QuestionGroup Question

How many COHow many CO22 molecules are there in 1.0 molecules are there in 1.0

cmcm3 3 of the Maxwell House Coffee of the Maxwell House Coffee Company extractor? How many more COCompany extractor? How many more CO22

molecules are there in a cmmolecules are there in a cm33 of the of the supercritical fluid in the Maxwell House supercritical fluid in the Maxwell House extractor than in a mole of COextractor than in a mole of CO22 at STP? at STP?

1 CHAPTER 11 Intermolecular Forces, Liquids and Solids.

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Transcript of 1 CHAPTER 11 Intermolecular Forces, Liquids and Solids.