INTERMOLECULAR INTERMOLECULAR FORCESFORCES

LIQUIDS & SOLIDSLIQUIDS & SOLIDS

Now it is time to consider the Now it is time to consider the forces forces

that condense matter. that condense matter.

These can be due to ionic or These can be due to ionic or

covalent bonding [intramolecular covalent bonding [intramolecular

forces — ionic stronger than forces — ionic stronger than

covalent] or much weaker covalent] or much weaker attractive attractive

forces we call intermolecular forces we call intermolecular forces. forces.

These are the forces These are the forces betweenbetween

(rather than within) molecules. (rather than within) molecules.

We briefly visited the IMF’s earlier We briefly visited the IMF’s earlier

when discussing the nonideal when discussing the nonideal behavior behavior

of gases. These forces cause of gases. These forces cause

changes of state by causing changes of state by causing changes changes

among the molecules, NOT within among the molecules, NOT within

them.them.

Dipole-DipoleDipole-DipoleStrongest IMF’sStrongest IMF’s

Molecules with Molecules with

dipoles orient dipoles orient

themselves so themselves so that that

““+” and “-” ends +” and “-” ends of of

the dipole are the dipole are

close together.close together.

Hydrogen BondsHydrogen Bonds

Dipole-dipole attraction in which Dipole-dipole attraction in which

hydrogen on one molecule is attracted hydrogen on one molecule is attracted

to a highly electronegative atom on an to a highly electronegative atom on an

adjacent molecule. (F, O, N) adjacent molecule. (F, O, N)

bonded H

H-“bond”

WHYWHY is there such variation among is there such variation among

the covalent hydrides of groups IV the covalent hydrides of groups IV

through VII? through VII?

One would expect that BP would One would expect that BP would

increase with increasing molecular increase with increasing molecular

mass [since the more electrons in a mass [since the more electrons in a

molecule, the more polarizable the molecule, the more polarizable the

cloud {more about that in the next cloud {more about that in the next

section}, the stronger the IMF’s, the section}, the stronger the IMF’s, the

more E needed to overcome these more E needed to overcome these

attractions and vaporize].attractions and vaporize].

Hydrogen bonding, Hydrogen bonding, That’s why!That’s why!

Both reasons enhance the IMF Both reasons enhance the IMF we we

refer to as hydrogen bonding.refer to as hydrogen bonding.

TWO ReasonsTWO Reasons

1. The lighter hydrides have the 1. The lighter hydrides have the highest En values which leads highest En values which leads to especially polar H-X bonds.to especially polar H-X bonds.

2. The small size of each dipole 2. The small size of each dipole

allows for a closer approach allows for a closer approach of of

the dipoles, further the dipoles, further strengthening strengthening

the attractions.the attractions.

London Dispersion ForcesLondon Dispersion ForcesWeakest IMF’sWeakest IMF’s

Relatively weak forces that Relatively weak forces that exist exist

among noble gas atoms and among noble gas atoms and

nonpolar molecules. (Ar, Cnonpolar molecules. (Ar, C88HH1818))

Caused by instantaneous dipole Caused by instantaneous dipole

formation, in which electron formation, in which electron

distribution becomes asymmetrical. distribution becomes asymmetrical.

The newly formed dipoles now find The newly formed dipoles now find

each other FAR more attractive than each other FAR more attractive than

before! before!

Dipole-induced dipole if an Dipole-induced dipole if an ion or ion or

polar moleculepolar molecule causes the distortion. causes the distortion.

OR OR

Induced dipole-induced dipole if a Induced dipole-induced dipole if a

nonpolar moleulenonpolar moleule sets off the chain sets off the chain

reaction of induction like in iodine.reaction of induction like in iodine.

a.k.a.a.k.a.

The ease with The ease with which the electron which the electron ““cloud” of an cloud” of an atom can be atom can be distorted is called distorted is called polarizabilitypolarizability. . You’ll want to You’ll want to write about write about polarizability when EXPLAINING polarizability when EXPLAINING these concepts.these concepts.

Without these forces, we could not Without these forces, we could not

liquefy covalent gases or solidify liquefy covalent gases or solidify

covalent liquids. covalent liquids.

These forces INCREASE as we go These forces INCREASE as we go

down the family since the electron down the family since the electron

cloud becomes more polarizable with cloud becomes more polarizable with

increasing FW [more principle E levels increasing FW [more principle E levels

added, more electrons present, more added, more electrons present, more

shielding, valence farther from the shielding, valence farther from the

nucleus, etc.]. nucleus, etc.].

Consider the halogens…Consider the halogens…

It explains WHY FIt explains WHY F22 and Cl and Cl22 are gases, are gases,

BrBr22 is a liquid [moderate dispersion is a liquid [moderate dispersion forces a.k.a. London forces, a.k.a. forces a.k.a. London forces, a.k.a. dipole-induced dipole forces] and dipole-induced dipole forces] and

ultimately Iultimately I22 is a solid! is a solid!

What does that tell us about What does that tell us about boiling points??boiling points??

Some Properties of a Some Properties of a LiquidLiquid

All of the following are greater All of the following are greater for for

polar molecules since their polar molecules since their IMF’s IMF’s

are greater than nonpolar are greater than nonpolar

molecules.molecules.

Surface TensionSurface Tension

The resistance to an increase in its The resistance to an increase in its

surface area (polar molecules). High surface area (polar molecules). High

ST indicates strong IMF’s. Molecules ST indicates strong IMF’s. Molecules

are attracted to each OTHER. are attracted to each OTHER.

A molecule in the interior of a liquid A molecule in the interior of a liquid

is attracted by the molecules is attracted by the molecules

surrounding it, whereas a molecule surrounding it, whereas a molecule

at the surface of a liquid is attracted at the surface of a liquid is attracted

only by the molecules below it and only by the molecules below it and

on each side.on each side.

Capillary ActionCapillary Action

Spontaneous rising of a liquid Spontaneous rising of a liquid

in a narrow tube.in a narrow tube.

Adhesive forces between molecule Adhesive forces between molecule

and glass overcome cohesive forces and glass overcome cohesive forces

between molecules themselves. between molecules themselves.

The narrower the tube, the more The narrower the tube, the more

surface area of glass, the higher the surface area of glass, the higher the

column of water climbs!column of water climbs!

The weight of the column sets the limit The weight of the column sets the limit

for the height achieved. Hg liquid for the height achieved. Hg liquid

behaves just the opposite. Water has a behaves just the opposite. Water has a

higher attraction for glass than itself so higher attraction for glass than itself so

its meniscus is inverted or concave, its meniscus is inverted or concave,

while Hg has a higher attraction for while Hg has a higher attraction for

other Hg molecules! Its meniscus is other Hg molecules! Its meniscus is

convex.convex.

ViscosityViscosity

Resistance to flow (molecules with Resistance to flow (molecules with

large intermolecular forces). large intermolecular forces).

Increases with molecular Increases with molecular complexity complexity

[long C chains get tanagles] and [long C chains get tanagles] and

increases with increasing IMF’s. increases with increasing IMF’s.

Glycerol [left] has Glycerol [left] has

3 OH groups 3 OH groups

which have a high which have a high

capacity for H-capacity for H-

bonding so this bonding so this

molecule is small, molecule is small,

but very viscous.but very viscous.

Gases have VERY SMALL IMFs and Gases have VERY SMALL IMFs and lots of motion. lots of motion.

Solids have VERY HIGH IMFs and Solids have VERY HIGH IMFs and next next

to no motion. to no motion.

Liquids have both strong IMFs Liquids have both strong IMFs andand quite a bit of motion. quite a bit of motion.

Modeling a liquid is Modeling a liquid is difficult.difficult.

Types of SolidsTypes of Solids

Crystalline SolidsCrystalline Solids

Highly regular arrangement of Highly regular arrangement of their their

components [often ionic, table components [often ionic, table salt salt

(NaCl), pyrite (FeS(NaCl), pyrite (FeS22)].)].

Amorphous solidsAmorphous solids

Considerable disorder in their Considerable disorder in their

structures (glass).structures (glass).

REPRESENTATION OFREPRESENTATION OFCOMPONENTS COMPONENTS

IN A IN A CRYSTALLINE SOLIDCRYSTALLINE SOLID

LatticeLattice

A 3-dimensional system of points A 3-dimensional system of points

designating the centers of designating the centers of

components (atoms, ions, or components (atoms, ions, or

molecules) that make up the molecules) that make up the

substance.substance.

Network CovalentNetwork Covalent

(a) carbon in diamond (a) carbon in diamond

formform

Here, each molecule is Here, each molecule is

covalently bonded to each covalently bonded to each

neighboring C with a neighboring C with a

tetrahedral arrangement. tetrahedral arrangement.

Graphite on the other hand, Graphite on the other hand, makes makes

sheets that slide and is MUCH sheets that slide and is MUCH softer! softer!

(pictured later)(pictured later)

(b) ionic salt (b) ionic salt

crystal latticecrystal lattice

(c) ice— notice the “hole” in the (c) ice— notice the “hole” in the hexagonal structure and all the hexagonal structure and all the

H-H- bonds. bonds. The “hole” The “hole” is why ice is why ice floats—it makes floats—it makes it less dense it less dense than the liquid!than the liquid!

X-RAY ANALYSIS X-RAY ANALYSIS OF SOLIDSOF SOLIDS

   X-ray DiffractionX-ray Diffraction

A bending or scattering of light. The A bending or scattering of light. The

beams of light are scattered from a beams of light are scattered from a

regular array of points in which the regular array of points in which the

spacing between the components spacing between the components are are

comparable with the λ of the light. comparable with the λ of the light.                                   

It is due to constructive It is due to constructive interference interference

when the waves of parallel when the waves of parallel beams beams

are in phase and to destructive are in phase and to destructive

interference when the waves are interference when the waves are

out of phase.out of phase.

The waves are in phase before they The waves are in phase before they

strike the crystal. strike the crystal.

IF the difference traveled after IF the difference traveled after

reflection is an reflection is an integral number of λintegral number of λ, ,

the waves will still be in phase.the waves will still be in phase.

                                    ..

Since the distance traveled after Since the distance traveled after

reflection depends on the distance reflection depends on the distance

between the atoms, the diffraction between the atoms, the diffraction

pattern can be used to determine pattern can be used to determine the the

inter-atomic spacing.inter-atomic spacing.

The diagram below shows two The diagram below shows two in-in-

phase waves being reflected by phase waves being reflected by

atoms in two different layers in atoms in two different layers in a a

crystal. crystal.

The extra distance traveled by The extra distance traveled by the the

lower wave is the sum of the lower wave is the sum of the

distances xy and yz and the distances xy and yz and the waves waves

will be in phase after reflection if: will be in phase after reflection if:

xy + yz = nλxy + yz = nλ

Trig time!Trig time!

If …If …

then, 2d sin θ = xy + yz = nλ then, 2d sin θ = xy + yz = nλ

[from above][from above]

where d is the distance between the where d is the distance between the atoms and θ is the angle of incidence atoms and θ is the angle of incidence and reflection. and reflection.

foreachd

yzxy

hypotenuse

opposite sin

Combine all of this and you get the Combine all of this and you get the

Bragg equation named after William Bragg equation named after William

Henry Bragg and his son William Henry Bragg and his son William

Lawrence Bragg who shared the Lawrence Bragg who shared the

Nobel Prize in physics in 1915 for Nobel Prize in physics in 1915 for

their pioneering work in x-ray their pioneering work in x-ray

crystallography. crystallography.

Do you know of any other Do you know of any other famous famous

x-ray crystallographers? x-ray crystallographers?

Why didn’t she win a Nobel Why didn’t she win a Nobel Prize?Prize?

Bragg Equation Bragg Equation

nλ = 2d sin θnλ = 2d sin θ

Exercise 1Exercise 1 Using the Bragg Equation Using the Bragg Equation

X-rays of wavelength 1.54 Å were X-rays of wavelength 1.54 Å were

used to analyze an aluminum crystal. used to analyze an aluminum crystal.

A reflection was produced at θ = 19.3 A reflection was produced at θ = 19.3

degrees. Assuming n = 1, calculate degrees. Assuming n = 1, calculate

the distance d between the planes of the distance d between the planes of

atoms producing this reflection.atoms producing this reflection.

SolutionSolution

d = 2.33 Å = 233 pmd = 2.33 Å = 233 pm

TYPES OF TYPES OF CRYSTALLINE SOLIDSCRYSTALLINE SOLIDS

    Ionic SolidIonic Solid

Contains ions at the points of the Contains ions at the points of the lattice that describe the structure lattice that describe the structure

of of the solid (NaCl). the solid (NaCl).

VERY high MP’s VERY high MP’s

Hard Hard

Ion-Ion Coulombic forces are the Ion-Ion Coulombic forces are the

strongest of all attractive forces. strongest of all attractive forces.

““IMF” usually implies covalently IMF” usually implies covalently

bonded substances, but can bonded substances, but can apply to apply to

both types.both types.

Molecular SolidMolecular Solid

Discrete covalently bonded Discrete covalently bonded

molecules at each of its lattice molecules at each of its lattice

points (sucrose, ice).points (sucrose, ice).

Atomic SolidAtomic Solid

Atoms of the substance are Atoms of the substance are

located at the lattice points. located at the lattice points.

Carbon—diamond, graphite and Carbon—diamond, graphite and

the fullerenes. Boron, and the fullerenes. Boron, and silicon silicon

as well.as well.

Know this Chart WellKnow this Chart Well

Structure and Bonding in Structure and Bonding in MetalsMetals

Metals are characterized by high Metals are characterized by high

thermal and electrical thermal and electrical conductivity, conductivity,

malleability, and ductility. These malleability, and ductility. These

properties are explained by the properties are explained by the

nondirectional covalent bonding nondirectional covalent bonding

found in metallic crystals.found in metallic crystals.

Closest PackingClosest Packing

A model that uses hard spheres A model that uses hard spheres to to

represent the atoms of a metal. represent the atoms of a metal.

These atoms are packed together These atoms are packed together

and bonded to each other equally and bonded to each other equally in in

all directionsall directions. .

It will be easiest for you to It will be easiest for you to

understand if you can imagine taking understand if you can imagine taking

a cubic box and pouring in golf balls. a cubic box and pouring in golf balls.

The balls will layer, perhaps directly The balls will layer, perhaps directly

on top of one another, but perhaps on top of one another, but perhaps

one layer slides into the “dimple” one layer slides into the “dimple”

made by the first layer so that the two made by the first layer so that the two

layers are offset a bit. layers are offset a bit.

Next, remove the golf balls and Next, remove the golf balls and

place tennis balls into the box. place tennis balls into the box.

They will fill the box differently They will fill the box differently

since they are of a different since they are of a different size.size.

In the diagram above, in each layer, In the diagram above, in each layer,

a given sphere is surrounded by six a given sphere is surrounded by six

others.others.

aba Packingaba Packing

The second layer is like the first, but The second layer is like the first, but it is displaced so that each sphere in it is displaced so that each sphere in the second layer occupies a dimple in the second layer occupies a dimple in the first layer. The spheres in the the first layer. The spheres in the

third third layer occupy dimples in the second layer occupy dimples in the second layer so that the spheres in the third layer so that the spheres in the third layer lie directly over those in the first layer lie directly over those in the first layer hence aba..layer hence aba..

aba has the hexagonal unit cell shown aba has the hexagonal unit cell shown

below and the resulting structure is below and the resulting structure is

hexagonal closest packed (hcp) hexagonal closest packed (hcp)

structure. structure. ababab….ababab….

abc Packingabc Packing

The spheres in the third layer The spheres in the third layer

occupy dimples in the second occupy dimples in the second layer layer

so that no spheres in the third so that no spheres in the third layer layer

lie above any in the first layer. The lie above any in the first layer. The

fourth layer is like the first.fourth layer is like the first.

abc has a face-centered cubic unit abc has a face-centered cubic unit

cell and the resulting structure is cell and the resulting structure is

cubic closest packed (ccp) structure. cubic closest packed (ccp) structure.

abcabc…abcabc…

The red sphere on The red sphere on

the right, the one in the right, the one in

the center of row ‘a’ the center of row ‘a’

that is not that is not numbered, numbered,

has 12 nearest has 12 nearest

neighbors. This one neighbors. This one

is hcp, but this is true is hcp, but this is true

for both types of for both types of

packing.packing.

Let’s consider a face-centered Let’s consider a face-centered

cubic cell…cubic cell…

A cubic cell is defined by the A cubic cell is defined by the centerscenters

of the spheres [atoms] on the cube’s of the spheres [atoms] on the cube’s

corners. corners.

How many corners are in a cube? How many corners are in a cube?

How many faces are in a cube? How many faces are in a cube?

Note that face centered means an Note that face centered means an

atom is stuck smack dab in the atom is stuck smack dab in the middle middle

of the face of one cube and of the face of one cube and

consequently, the adjacent cube—1/2 consequently, the adjacent cube—1/2

in each! in each!

How many spheres [atoms] are in How many spheres [atoms] are in one one

cube that is face-centered? cube that is face-centered?

Exercise 2 Calculating the Exercise 2 Calculating the Density of a Closest Packed Density of a Closest Packed SolidSolidSilver crystallizes in a cubic closest Silver crystallizes in a cubic closest

packed structure. The radius of a packed structure. The radius of a silver silver

atom is 144 pm. atom is 144 pm.

Calculate the Calculate the

density of solid density of solid

silver.silver.

SolutionSolution

density = 10.6 g/cmdensity = 10.6 g/cm33

Bonding Models for Bonding Models for MetalsMetals

Remember, metals conduct Remember, metals conduct heat heat

and electricity, are malleable and electricity, are malleable and and

ductile, and have high melting ductile, and have high melting

points. points.

These facts indicate that the These facts indicate that the

bonding in most metals is both bonding in most metals is both

strong and nondirectional. strong and nondirectional. Difficult Difficult

to separate atoms, but easy to to separate atoms, but easy to

move them provided they stay in move them provided they stay in

contact with each other!contact with each other!

Electron Sea ModelElectron Sea Model

A regular array of metals in a A regular array of metals in a “sea” “sea”

of electrons. of electrons.

I A & II A metals pictured belowI A & II A metals pictured below..

Band (Molecular Orbital) Band (Molecular Orbital) ModelModel

Electrons assumed to travel Electrons assumed to travel aroundaround

metal crystal in MO’s formed metal crystal in MO’s formed from from

valence atomic orbitals of valence atomic orbitals of metal metal

atoms.atoms.

Metal AlloyMetal Alloy

A substance A substance that that

has a mixture of has a mixture of

elements and elements and has has

metallic metallic properties. properties.

Substitution AlloysSubstitution Alloys

In brass, 1/3 of the atoms in the In brass, 1/3 of the atoms in the

host copper metal have been host copper metal have been

replaced by zinc atoms. replaced by zinc atoms.

Sterling silver—93% silver and 7% Sterling silver—93% silver and 7%

copper. copper.

Pewter—85% tin, 7% copper, 6% Pewter—85% tin, 7% copper, 6%

bismuth and 2% antimony. bismuth and 2% antimony.

Plumber’s solder—95% tin and 5% Plumber’s solder—95% tin and 5%

antimony.antimony.

Interstitial AlloyInterstitial Alloy

Formed when some of the Formed when some of the

interstices [holes] in the closest interstices [holes] in the closest

packed metal structure are packed metal structure are occupied occupied

by small atoms. by small atoms.

Steel—carbon is in the holes of an Steel—carbon is in the holes of an

iron crystal. iron crystal.

There are many different types of There are many different types of

steels. All depend on the steels. All depend on the

percentage of carbon in the iron percentage of carbon in the iron

crystal.crystal.

NETWORK ATOMIC NETWORK ATOMIC SOLIDSSOLIDS

a.k.a. a.k.a. Network CovalentNetwork Covalent

Composed of strong Composed of strong directional directional

covalent bonds that are best covalent bonds that are best

viewed as a “giant molecule”. viewed as a “giant molecule”.

Both diamond and graphite are Both diamond and graphite are

network solids. The difference is network solids. The difference is

that diamond bonds with that diamond bonds with neighbors neighbors

in a tetrahedral 3-D fashion, while in a tetrahedral 3-D fashion, while

graphite only has weak bonding in graphite only has weak bonding in

the 3rd dimension. the 3rd dimension.

Network Solids are Often Network Solids are Often BrittleBrittle

Diamond is the hardest substance Diamond is the hardest substance on on

the planet, but when a diamond is the planet, but when a diamond is

““cut” it is actually fractured to make cut” it is actually fractured to make

the facets.the facets.

Do not conduct heat or electricityDo not conduct heat or electricity

Carbon, silicon-basedCarbon, silicon-based

Diamond is hard, Diamond is hard,

colorless and an colorless and an

insulator. insulator.

It consists of carbon atoms ALL It consists of carbon atoms ALL

bonded tetrahedrally, therefore spbonded tetrahedrally, therefore sp33

hybridization and 109.5hybridization and 109.5 bond bond angles.angles.

Graphite is slippery, black and Graphite is slippery, black and a a

conductor. conductor.

Graphite is bonded so that it Graphite is bonded so that it forms forms

layers of carbon atoms arranged layers of carbon atoms arranged

infused six-membered rings. infused six-membered rings.

This indicates spThis indicates sp22 hybridization and hybridization and 120120 bond angles within the fused bond angles within the fused rings. rings.

The unhybridized p orbitals are The unhybridized p orbitals are perpendicular to the layers and form perpendicular to the layers and form bonds.bonds.

The delocalized electrons in the The delocalized electrons in the bonds account for the electrical bonds account for the electrical

conductivity while also contributing to conductivity while also contributing to

the mechanical stability of the layers. the mechanical stability of the layers.

It is often used as a lubricant in It is often used as a lubricant in

locks—grease or oil collects dirt, locks—grease or oil collects dirt,

graphite does not.graphite does not.

Silicon is to geology what carbon Silicon is to geology what carbon is is

to biology! to biology!

The most significant silicon The most significant silicon

compounds involve chains with compounds involve chains with

silicon-oxygen bonds.silicon-oxygen bonds.

SilicaSilica

Empirical formula SiOEmpirical formula SiO22—not at all like —not at all like

its cousin COits cousin CO22! !

Quartz and some types of sand are Quartz and some types of sand are

silicon dioxide as opposed to a clear silicon dioxide as opposed to a clear

colorless gas such as carbon dioxide. colorless gas such as carbon dioxide.

Why Such Drastic Why Such Drastic Differences?Differences?

Bonding.Bonding.

Draw the Lewis Structure for Draw the Lewis Structure for COCO2.2.

What is carbon’s hybridization? What is carbon’s hybridization?

Silicon cannot use its valence 3p Silicon cannot use its valence 3p

orbitals to form strong orbitals to form strong bonds with bonds with

oxygen, mainly due to the larger oxygen, mainly due to the larger

size of the silicon atom and its size of the silicon atom and its

orbitals—you get inefficient overlap. orbitals—you get inefficient overlap.

INSTEAD of INSTEAD of

forming forming bonds, bonds,

the silicon atom the silicon atom

satisfies the octet satisfies the octet

rule by forming rule by forming

single σ bonds single σ bonds

with FOUR with FOUR

OXYGEN atoms. OXYGEN atoms.

Each silicon is in the center of a Each silicon is in the center of a

tetrahedral arrangement of oxygen tetrahedral arrangement of oxygen

atoms. atoms.

This means that although the This means that although the empirical empirical

formula is SiOformula is SiO22, the structure is based , the structure is based

on a network of SiOon a network of SiO44 tetrahedra with tetrahedra with

sharedshared oxygen atoms. oxygen atoms.

Silicates are the compounds found Silicates are the compounds found in in

most rocks, soils and clays. most rocks, soils and clays.

Silicates contain a O/Si ratio greater Silicates contain a O/Si ratio greater

than 2:1 and contain silicon-oxygen than 2:1 and contain silicon-oxygen

anionsanions. .

That means silicates are salts That means silicates are salts

containing metallic cations that containing metallic cations that are are

needed to make neutral needed to make neutral arrangements. arrangements.

Common Common

silicate silicate

anions are anions are

pictured on pictured on

the right.the right.

When silica is heated above its MP of When silica is heated above its MP of

about 1600about 1600C and cooled rapidly, an C and cooled rapidly, an

amorphous [“without shape”—not a amorphous [“without shape”—not a

crystal] solid forms. crystal] solid forms.

We call it glass. It’s really a We call it glass. It’s really a

supercooled, ultra viscous liquid with supercooled, ultra viscous liquid with

a great deal of disorder. a great deal of disorder.

At left, At left,

a) is quartz, while a) is quartz, while

b) is quartz glass. b) is quartz glass.

These pictures These pictures are are

2-D, not 3-D.2-D, not 3-D.

Common glass results when Common glass results when NaNa22COCO33

is added to the silica melt.is added to the silica melt.

Pyrex®, a borosilicate glass [lab Pyrex®, a borosilicate glass [lab

ware] is made when Bware] is made when B22OO33 is added is added

to the silica melt. to the silica melt.

Eyeglasses are made from glass Eyeglasses are made from glass

that is especially hard so it can that is especially hard so it can be be

ground into precise shapes. ground into precise shapes.

KK22O has been added.O has been added.

Read the sections in your book Read the sections in your book

about ceramics and about ceramics and semiconductors! semiconductors!

Molecular SolidsMolecular Solids

Simply where a molecule occupies Simply where a molecule occupies

the lattice position rather than an the lattice position rather than an

atom. atom.

Ice & dry ice [solid carbon dioxide] Ice & dry ice [solid carbon dioxide]

are examples. are examples.

Allotropes of sulfur and Allotropes of sulfur and

phosphorous are included. phosphorous are included.

SS88 or P or P44 occupy the lattice positions occupy the lattice positions

in these allotropes [many forms] of in these allotropes [many forms] of

these elements. these elements.

Characterized by strong Characterized by strong covalent covalent

bonding bonding withinwithin the molecule, the molecule, yet yet

weak forces weak forces betweenbetween the the

molecules.molecules.

It takes 6 kJ of energy to melt one It takes 6 kJ of energy to melt one

mole of solid water since you only mole of solid water since you only

have to overcome H-bonding while have to overcome H-bonding while

it takes 470 kJ of energy to break it takes 470 kJ of energy to break

one mole of O—H bonds.one mole of O—H bonds.

Molecules such as COMolecules such as CO22, I, I22, P, P44, and , and

SS88 have no dipole moment. have no dipole moment.

We call their IMF’s:We call their IMF’s:

London Dispersion ForcesLondon Dispersion Forces

As the size of the molecule As the size of the molecule increases increases

[often reported in a Chem I book as [often reported in a Chem I book as

““increased MM”], the London increased MM”], the London

dispersion forces increase because dispersion forces increase because

the larger the molecule, the more the larger the molecule, the more

electrons, the more polarizable its electrons, the more polarizable its

electron cloudelectron cloud..

If it is more polarizable, If it is more polarizable, temporary temporary

dipoles can easily form which dipoles can easily form which shifts shifts

the IMF’s from weak London the IMF’s from weak London

dispersion to a weak form of dispersion to a weak form of

induced dipole-induced dipole.induced dipole-induced dipole.

So What?So What?

The MP and BP increase since The MP and BP increase since the the

molecules are MORE attracted molecules are MORE attracted to to

each other as a result of this each other as a result of this

polarizing of the electron cloud. polarizing of the electron cloud.

When molecules When molecules

DO have dipole DO have dipole

moments, their moments, their

IMF’s are IMF’s are greater, greater,

especially if H-especially if H-

bonding is bonding is

present. It’s like present. It’s like

an added bonus.an added bonus.

Bonded H

H-bond, an IMF

Ionic SolidsIonic Solids

Stable, high-melting substances Stable, high-melting substances

held together by STRONG held together by STRONG

electrostatic forces that exist electrostatic forces that exist

between oppositely charged between oppositely charged ions.ions.

Exercise 4 Exercise 4 Types of Solids Types of SolidsUsing Table 10.7, classify each of the Using Table 10.7, classify each of the

following substances according to the following substances according to the

type of solid it forms.type of solid it forms.

a. a. GoldGold

b. b. Carbon dioxideCarbon dioxide

c. c. Lithium fluorideLithium fluoride

d. d. Krypton Krypton

SolutionSolution

A: atomic solid w/metallic propertiesA: atomic solid w/metallic properties

B: molecular solid B: molecular solid

C: binary ionic solid C: binary ionic solid

D: atomic solid w/ properties D: atomic solid w/ properties

characteristic of molecular solid characteristic of molecular solid

w/nonpolar moleculesw/nonpolar molecules

VAPOR PRESSURE VAPOR PRESSURE AND AND

CHANGES OF STATECHANGES OF STATE

Vaporization or Vaporization or EvaporationEvaporation

When molecules of a liquid can escape When molecules of a liquid can escape

the liquid’s surface and form a gas. the liquid’s surface and form a gas.

ENDOTHERMIC,ENDOTHERMIC, since energy must be since energy must be

absorbed so that the liquid molecules absorbed so that the liquid molecules

gain enough energy to escape the gain enough energy to escape the

surface and thus overcome the liquid’s surface and thus overcome the liquid’s

IMFs.IMFs.

HHvap vap -- Enthalpy of Enthalpy of VaporizationVaporization

The energy required to vaporize The energy required to vaporize ONE ONE

mole of a liquid at 1 atm pressure.mole of a liquid at 1 atm pressure.

Water’s heat of vaporization is 40.7 Water’s heat of vaporization is 40.7

kJ/mol. kJ/mol.

This is huge! This is huge!

Water makes life on this planet Water makes life on this planet

possible since it acts as a coolant. possible since it acts as a coolant.

The reason it’s The reason it’s HHvapvap is so large is so large

has everything to do with has everything to do with hydrogen hydrogen

bonding. bonding.

The IMFs in water are huge, thus a The IMFs in water are huge, thus a

great deal of the sun’s energy is great deal of the sun’s energy is

needed to evaporate the rivers, needed to evaporate the rivers, lakes, lakes,

oceans, etc. of Earth. oceans, etc. of Earth.

Perspiration is a coolant for Perspiration is a coolant for animals animals

possessing sweat glands. Energy possessing sweat glands. Energy

from your hot body is absorbed by from your hot body is absorbed by

the water solution to evaporate.the water solution to evaporate.

CondensationCondensation

Opposite of vaporization. When the Opposite of vaporization. When the

energetic steam molecules energetic steam molecules generated generated

by your morning shower hurl by your morning shower hurl

themselves across the bathroom and themselves across the bathroom and

collide with the cold mirror, they lose collide with the cold mirror, they lose

energy and return to the liquid energy and return to the liquid

phase.phase.

Equilibrium Vapor Equilibrium Vapor PressurePressureReached when the rate of Reached when the rate of

evaporation evaporation

equals the equals the

rate of rate of

condensation condensation

in a closed in a closed

container.container.

Stopper a flask of a freshly poured Stopper a flask of a freshly poured liquid. liquid.

(a). Equilibrium VP (a). Equilibrium VP will be established. will be established.

(b).Moleucles leave (b).Moleucles leave and enter the liquid and enter the liquid phase @ the phase @ the SAME RATE.SAME RATE.

(a) The VP of a (a) The VP of a

liquid can be liquid can be

measured easily measured easily

using using a using using a

simple simple barometer.barometer.

(b) The three liquids water, ethanol, and (b) The three liquids water, ethanol, and

diethyl ether have quite different vapor diethyl ether have quite different vapor

pressures. Ether is by far the most volatile pressures. Ether is by far the most volatile

of the three [escapes easiest]. Note that of the three [escapes easiest]. Note that

in each case a little liquid remains (floating in each case a little liquid remains (floating

on the mercury).on the mercury).

VolatileVolatile

Have high VP, thus low IMFs. These Have high VP, thus low IMFs. These liquids evaporate readily from open liquids evaporate readily from open containers since they have so little containers since they have so little attraction for each other. It takes attraction for each other. It takes

very very little energy being absorbed in order little energy being absorbed in order for them to escape the surface of the for them to escape the surface of the liquid. liquid.

The heat energy absorbed from a The heat energy absorbed from a

warm room is usually enough to warm room is usually enough to make make

these substances evaporate these substances evaporate quickly. quickly.

If there is an odor to the If there is an odor to the substance, substance,

these are the liquids you smell these are the liquids you smell

almost as soon as you open the almost as soon as you open the

bottle! The molecules have been bottle! The molecules have been

banging against the lid wanting banging against the lid wanting out!out!

VP increases significantly with VP increases significantly with

temperature! temperature!

Heat ‘em up, Heat ‘em up,

Speed ‘em up, Speed ‘em up,

Move ‘em out! Move ‘em out!

Increasing the temperature increases Increasing the temperature increases

the KE which facilitates escape AND the KE which facilitates escape AND

the speed of the escapees! They the speed of the escapees! They

bang into the sides of the container bang into the sides of the container

with more frequency [more of them with more frequency [more of them

escape] and more energy [more escape] and more energy [more

momentum].momentum].

More molecules can attain the More molecules can attain the

energy needed to overcome the energy needed to overcome the

IMFs in a liquid at a higher T since IMFs in a liquid at a higher T since

the KE increases.the KE increases.

In General, as MM In General, as MM VP VP

BECAUSE, as molecules increase BECAUSE, as molecules increase in in

molar mass, they also increase in molar mass, they also increase in the the

number of electrons. number of electrons.

As the number of electrons increase, As the number of electrons increase,

the polarizability of the molecule the polarizability of the molecule

increases so more induced dipole-increases so more induced dipole-

induced dipole or dispersion forces induced dipole or dispersion forces

exist, causing stronger attractions to exist, causing stronger attractions to

form form betweenbetween molecules. This molecules. This

decreases the number of molecules decreases the number of molecules

that escape and thus lowers the VP. that escape and thus lowers the VP.

H-bonding causes a major exception! H-bonding causes a major exception!

It’s presence greatly increases the It’s presence greatly increases the

IMFs of the liquid. IMFs of the liquid.

Water has an incredibly low VP for Water has an incredibly low VP for

such a light [MM = 18.02] molecule.such a light [MM = 18.02] molecule.

We can put the math to this. We can put the math to this.

Plot ln VP vs. 1/T [in Kelvins] and Plot ln VP vs. 1/T [in Kelvins] and we we

get a straight line. get a straight line.

Next, put this into y = mx + b Next, put this into y = mx + b

format:format:

CTR

HVP vap

1

ln

R is the universal gas constant. R is the universal gas constant.

Since this is all about energy, use Since this is all about energy, use

the “energy” R, 8.31 J/K.the “energy” R, 8.31 J/K.

C is a constant characteristic C is a constant characteristic of of

the liquid [y-intercept].the liquid [y-intercept].

slope, m = slope, m = R

H vap

Exercise 5Exercise 5 Determining Determining Enthalpies of VaporizationEnthalpies of Vaporization

Using the plots Using the plots

shown, determine shown, determine

whether water or whether water or

diethyl ether has diethyl ether has

the larger the larger enthalpy enthalpy

of vaporization.of vaporization.

SolutionSolution

= water= water

If we know the values of If we know the values of Hvap Hvap

and VP at one temperature we can and VP at one temperature we can

solve the above expression for the solve the above expression for the

constant, C, and set a second constant, C, and set a second

expression for T2 equal to the first expression for T2 equal to the first

since the value of C is NOT since the value of C is NOT

dependent upon temperature.dependent upon temperature.

which can be rearranged intowhich can be rearranged into

22

11 lnln

RT

HVPC

RT

HVP vapvap

122

1 11ln

TTR

H

VP

VP vap

This form is called the This form is called the

Clausius-Clapeyron Clausius-Clapeyron Equation.Equation.

Exercise 6Exercise 6 Calculating Vapor PressureCalculating Vapor Pressure

The vapor pressure of water at 25°C is The vapor pressure of water at 25°C is

23.8 torr, and the heat of vaporization 23.8 torr, and the heat of vaporization

of water at 25°C is 43.9 kJ/mol. of water at 25°C is 43.9 kJ/mol.

Calculate the vapor pressure of water Calculate the vapor pressure of water

at 50°C.at 50°C.

SolutionSolution

= 93.7 torr= 93.7 torr

SublimationSublimation

Solids also have vapor Solids also have vapor

pressures. Some solids pressures. Some solids

go directly to the vapor go directly to the vapor

phase at 1atm, skipping phase at 1atm, skipping

the liquid phase all the liquid phase all

together! Iodine and dry ice together! Iodine and dry ice [solid [solid

carbon dioxide] both do this. carbon dioxide] both do this.

Melting PointMelting Point

A heating curve A heating curve is pictured here. is pictured here. Molecules break Molecules break loose from lattice loose from lattice points and solid changes to liquid. points and solid changes to liquid. (Temperature is constant as (Temperature is constant as

melting melting occurs.) PE is changing like crazy occurs.) PE is changing like crazy while KE remains constant! while KE remains constant!

HHfusfus, Enthalpy of Fusion, Enthalpy of Fusion

The enthalpy change that occurs at the The enthalpy change that occurs at the

melting point [which is the freezing melting point [which is the freezing

point, by the way]. This energy is point, by the way]. This energy is

clearly going into increasing the PE of clearly going into increasing the PE of

the molecules since the temperature or the molecules since the temperature or

average KE of the molecules is average KE of the molecules is

plateaued, or staying the same.plateaued, or staying the same.

vapor pressure of solid vapor pressure of solid

= =

vapor pressure of liquid vapor pressure of liquid

[equilibrium is established][equilibrium is established]

On the plateaus, calculate the E On the plateaus, calculate the E change using change using

q = q = HH[vap or fus][vap or fus]mm

On the slants, calculate the E On the slants, calculate the E change change

usingusingq = mcq = mcTT

The melting and boiling points of water The melting and boiling points of water

are determined by the vapor pressures are determined by the vapor pressures

of the solid and liquid states.of the solid and liquid states.

This figure shows VP of solid and This figure shows VP of solid and

liquid water as a function of liquid water as a function of

temperatures temperatures

near zero.near zero.

Below zero—VP of ice has a larger Below zero—VP of ice has a larger

T-Dependence.T-Dependence.

This means the VP of ice increases This means the VP of ice increases

more rapidly than the liquid’s VP more rapidly than the liquid’s VP for for

each increase in temperature. each increase in temperature.

A point is eventually reached A point is eventually reached where where

the the

VP solid = VP liquid.VP solid = VP liquid.

We call this temperature the MP!We call this temperature the MP!

Normal Melting PointNormal Melting Point

The temperature at which the The temperature at which the

VP solid = VP liquid VP solid = VP liquid

AND AND

P total = 1atmP total = 1atm

Normal Boiling PointNormal Boiling Point

The temperature at which theThe temperature at which the

VP liquid = exactly 1 atmVP liquid = exactly 1 atm

FREAKSFREAKS

Changes of Changes of

state do not state do not

always always

form at the form at the

exact MP exact MP

and BP’s. and BP’s.

SupercooledSupercooled

Oxymoron—the substance is at a Oxymoron—the substance is at a

temperature below its FP, yet it temperature below its FP, yet it

remains a liquid. Usually happens remains a liquid. Usually happens

when the cooling has been gradual when the cooling has been gradual

and the degree of organization and the degree of organization

needed to form crystals hasn’t needed to form crystals hasn’t

happened. happened.

At some point, organization At some point, organization

happens and the solid is readily happens and the solid is readily

formed, the temperature rises formed, the temperature rises back back

to the MP as the heat of to the MP as the heat of

crystallization is released.crystallization is released.

SuperheatedSuperheated

Another oxymoron—the substance Another oxymoron—the substance

is at a temperature above its BP, is at a temperature above its BP,

yet it remains a liquid. Usually yet it remains a liquid. Usually

happens when heated very rapidly happens when heated very rapidly

[microwave oven] and bubbles form [microwave oven] and bubbles form

in the interior with high internal in the interior with high internal

pressures.pressures.

They often burst before reaching They often burst before reaching

the surface making quite a mess the surface making quite a mess of of

things! things!

Really ruins an experiment. Really ruins an experiment.

This is called bumping in the lab. This is called bumping in the lab.

Prevent it by adding boiling chips to Prevent it by adding boiling chips to the the

flask. These chips are porous and flask. These chips are porous and

have air trapped in them, upon have air trapped in them, upon heating heating

tiny air bubbles form and act as tiny air bubbles form and act as

““starters” for vapor bubble formation.starters” for vapor bubble formation.

PHASE DIAGRAMSPHASE DIAGRAMSClosed Systems Closed Systems

Represents phases as a function of Represents phases as a function of

temperature and pressure.temperature and pressure.

Critical TemperatureCritical Temperature

Temperature above which the Temperature above which the vapor vapor

cannot be liquefied.cannot be liquefied.

Critical PressureCritical Pressure

Pressure required to liquefy AT the Pressure required to liquefy AT the

critical temperature.critical temperature.

Critical PointCritical Point

Critical temperatue and pressure Critical temperatue and pressure

(for water, Tc = 374° C and 218 (for water, Tc = 374° C and 218 atm).atm).

The solid-liquid line tilts to the left The solid-liquid line tilts to the left [negative slope] since it’s solid is [negative slope] since it’s solid is

lessless dense than it’s liquid phase—ice dense than it’s liquid phase—ice floats. floats.

Usually the solid sinks as it is more Usually the solid sinks as it is more dense.dense.

Water is a Freak!Water is a Freak!

Consider the Consider the cylinder pictured cylinder pictured here.here.

Experiment 1Experiment 1

P = 1atm. P = 1atm.

Completely filled with ONLY ice Completely filled with ONLY ice at at

-20-20C. C.

Heat…Heat…

-20 -20 0 only ice present at 0, ice 0 only ice present at 0, ice melts [no vapor]melts [no vapor]

Past 0, liquid water begins to exert Past 0, liquid water begins to exert

a VP. a VP.

When the VP of the liquid reaches When the VP of the liquid reaches

1atm, vaporization occurs and 1atm, vaporization occurs and

steam is formed.steam is formed.

Experiment 2Experiment 2

P = 2.0 torrP = 2.0 torr

Start again with only ice at - 20Start again with only ice at - 20C. C.

Heat…Heat…

As heating proceeds, -10 is reached As heating proceeds, -10 is reached

where ice changed directly to where ice changed directly to vapor. vapor.

It sublimes. It sublimes.

No liquid water forms No liquid water forms becausebecause the the

VP of water is always greater than VP of water is always greater than

2.0 torr. If water were placed into 2.0 torr. If water were placed into

the cylinder at these conditions, it the cylinder at these conditions, it

would freeze if less than -10 or would freeze if less than -10 or

vaporize if greater than -10. vaporize if greater than -10.

Water cannot exist at these Water cannot exist at these conditions!conditions!

Experiment 3Experiment 3

P = 4.588 torrP = 4.588 torr

Start again with only ice at -20Start again with only ice at -20C. C.

Heat…Heat…

No new phase results until the No new phase results until the

temperature reaches 0.0098temperature reaches 0.0098C. C.

This is the triple point of water This is the triple point of water and and

all THREE phases exist in all THREE phases exist in

equilibrium at this set of P & T equilibrium at this set of P & T

conditions.conditions.

Experiment 4Experiment 4

P = 225 atmP = 225 atm

Start this time with only liquid Start this time with only liquid water water

in the cylinder at 300in the cylinder at 300C. C.

Heat….Heat….

The liquid water gradually changes The liquid water gradually changes

to vapor, but it goes through a to vapor, but it goes through a fluid fluid

state that was not present at any state that was not present at any of of

the other pressures and the other pressures and

temperatures. temperatures.

This fluid region, is neither true This fluid region, is neither true liquid liquid

nor true vapor. This occurs when nor true vapor. This occurs when the the

critical point has been exceeded. critical point has been exceeded.

For water:For water:

CT = 374CT = 374C and CP = 218 C and CP = 218 atm.atm.

What is the effect of pressure What is the effect of pressure on on

ice? ice?

It melts it.It melts it.

You can take a block of ice, You can take a block of ice, connect connect

a wire to two heavy weights and a wire to two heavy weights and

drape it across the block. drape it across the block.

The wire will exert pressure on the The wire will exert pressure on the

block, melt it and begin a journey block, melt it and begin a journey

downward through the block due to downward through the block due to

the force of gravity acting on the the force of gravity acting on the

weights. weights.

The “cool” thing [pun intended] The “cool” thing [pun intended]

is that after the wire has left is that after the wire has left the the

surface, the block refreezes!surface, the block refreezes!

Most substances have a solid-Most substances have a solid-

liquid line that has a positive liquid line that has a positive slope slope

since their solid since their solid

phase is more phase is more

dense than the dense than the

liquid. This one liquid. This one

is for carbon is for carbon

dioxide. dioxide.

Each phase Each phase

boundary boundary

represents an represents an

equilibrium set equilibrium set

of pressure of pressure and and

temperature temperature

conditions!!conditions!!