Unit 5 (Chp 11,13)

Bonds & IMAFs inLiquids, Solids, and

SolutionsJohn D. Bookstaver

St. Charles Community College

St. Peters, MO

2006, Prentice Hall, Inc.

Chemistry, The Central Science, 10th editionTheodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

Attractions

Intra–(strong)

Inter–(weak)

“Bonds” “IMAFs”

??

?

Ionic(metal–

nonmetal)

Covalent(nonmetals)

polarnon-polar

Intermolecular Attractive ForcesIntramolecular Attraction (within)

(strong bonds)

(weak)Intermolecular Attraction (between)

Which attraction is overcome (broken) by melting & vaporizing? weak IMAFs

between molecules

Intermolecular Attractive Forces

IMAFs determine physical properties such as boiling & melting points, vapor pressure, and viscosity.

bp, mp, vp, visc.

Intramolecular Attraction (within) (strong bonds)

(weak)Intermolecular Attraction (between)

States of MatterThe main difference between phases of matter is the distance between particles.

changes of state

States of MatterState (distance between particles) at a certain

T and P depends on two opposing qualities:

IMAFs(intermolecular attractive forces

between particles)

KE(kinetic energy of the particles

vs.

Attractions

Intra–(strong)

Ionic(metal–

nonmetal)

Covalent(nonmetals)

polar non-polar

Inter–(weak)

“Bonds” “IMAFs”

?

At that instant, the He atom is polar (instantaneous dipole).

(excess of e–’s on one side, and shortage on the other)

Electrons in the 1s orbital of He repel each other, BUT…

they occasionally wind up on the same side of the atom.

London Dispersion Forces

d- d+

London Dispersion Forces

instantaneous dipole

induced dipole

causes

LDFs:attractions between instantaneous dipoles and induced dipoles caused by motion of e–’s.

d- d+

d- d+

London Dispersion Forces• present in all molecules,

(polar & nonpolar)

• The tendency of an electron cloud to distort to become temporarily polar in this way is called ___________.polarizabilityd- d+ d- d+

Factors Affecting London Forces

• LDFs increase with increased MW b/c…

larger e– clouds, are more polarizable.

(use this phrase to answer FR question)

MW (molecular weight)

Factors Affecting London Forces

• long, skinny molecules have stronger IMAFs due to……increased surface area to form more attractions.

(SAcylinder > SAsphere)

Shape

Attractions

Intra–(strong)

Ionic(metal–

nonmetal)

Covalent(nonmetals)

polar non-polar

Inter–(weak)

“Bonds” “IMAFs”

?London

dispersion forces

(nonpolar & all)

Dipole-Dipole Interactions

• Polar molecules with permanent dipoles are attracted to each other.

(dipole) (dipole)

Dipole-Dipole Interactions

The more polar the molecule,the higher the boiling/melting point.

(due to greater dipole-dipole IMAFs that require more energy to overcome)

?

DEN

polar bonds

assym. shape

Which Have a Greater Effect:Dipole-Dipole Interactions or Dispersion Forces?

•dipole–dipole interactions (permanent dipoles) are typically stronger than LDFs (temporary dipoles as instantaneous–induced).

•But much larger molecules could have LDFs that are stronger than dipole-dipole interactions.

(larger e– clouds, are more polarizable)

Attractions

Intra–(strong)

Ionic(metal–

nonmetal)

Covalent(nonmetals)

polar non-polar

Inter–(weak)

London dispersion

forces(all, nonpolar)

dipole–dipole(polar)

“Bonds” “IMAFs”

?

nonpolar

polar

Boiling Points

How Do We Explain This?

•unusually high bp•unusually strong IMAFs

• H-bonds are caused by an electron deficient H atoms (bonded to N, O, or F) attracted tosmall, very electronegative N, O, or F atoms on a nearby molecule.

Hydrogen Bonding

Attractions

Intra–(strong)

Ionic(metal–

nonmetal)

Covalent(nonmetals)

polar non-polar

Inter–(weak)

London dispersion

forces(all, nonpolar)

dipole–dipole(polar)

H–bondsH with N, O, F?

“Bonds” “IMAFs”

Ion-Dipole Interactions• ionic solutes dissolve in polar solvents

OH

H

OH

H

Na+ Cl–

Attractions

Intra–(strong)

Ionic(metal–

nonmetal)

Covalent(nonmetals)

polar non-polar

Inter–(weak)

London dispersion

forces(all, nonpolar)

dipole–dipole(polar)

H–bondsH with N, O, F

ion–dipole(aq ions)

“Bonds” “IMAFs”

Intermolecular Attractive Forces

Stronger

Weaker

H-bonds(if H with N, O, or F)

dipole-dipole int.’s(polar molecules)

London dispersion forces(nonpolar, instant–induced dipoles)

• London dispersion forces (LDFs) only• bp increases as length of chain b/c…

…larger e– cloud, more polarizable

Organic Functional Groups

Alkanes

polar & H-bond

polar

Organic Functional GroupsWhat IMAFs?

Organic Functional GroupsWhat IMAFs?

polar

polar

polar

polar

& H-bond

& H-bond

H-bond

3–pentanone(ketone)

propanal (aldehyde)

ethylamine(amine)

ethanoic acid (carboxylic acid)

trimethylamine(amine)

dipole-dipole

dipole-dipole

dipole-dipole

H-bondbutane(alkane)

LDFs

ethanol(alcohol)

H-bond

IMAFs in Protein Structure & DNA

aminoacid

H bonds

IMAFs in Protein Structure & DNA1

23

4H

bonds

IMAFs in Protein Structure & DNA

H-bonds H-bonds

HWp. 476

Intermolecular Forces Affect Many Physical Properties

The strength of the attractions between particles can greatly affect the physical properties of a substance or solution.

Cohesive• to each other

Adhesive• to surface

Cohesive/Adhesive Forces

cohesive

adhesive

glass

Capillary Action

• due to co/adhesive forces

results from thenet inward force experienced by the molecules on the surface of a liquid.

Surface Tension

• resistance of a liquid to flow

• increases with IMAF’s and decreases with higher temp.

Viscosity

HW p. 479 #29

Phase ChangesHW p. 479

#34

• Heat of Fusion (Hfus): energy to change (s) to (l) at melting point.

Energy and Phase Changes

Energy and Phase Changes

• Heat of Vaporization (Hvap): energy to change (l) to (g) at boiling point.

DEMO: butane

What happens to added KE?

Temp. does not change during phase change.

Energy and Phase Changes

Added energy

separates particles

(overcome IMAFs)

HWp. 480

#3547a

liquid molecules escape to vapor

Vapor Pressuremore volatile

=more vapor

pressure above liquid

gas molecules condense to liquid

(dynamic equilibrium)

=_____ IMAFSweak

Vapor Pressure• As T ↑, the fraction of molecules that have

enough energy to escape increases.

As more molecules escape the liquid, the pressure they exert increases.

Dynamic Equilibrium:vaporize/condense at same rate

Vapor Pressure

Vapor Pressure

•boiling point:T at which

vapor pressure=

atmospheric pressure

•normal b.p.:T at which

v.p. = 1 atm

HW p. 480 #47b, 48

DEMO: boil H2O

Solutions• homogeneous mixtures of

pure substances.• solute is dispersed uniformly

throughout the solvent.

+

Why does stuff dissolve?

IMAFs betweensolute–solvent

must be stronger

IMAFs between solute–solute

solvent–solventsolvated

(dissolved)

For Ionic Solutes…

Ions are soluble in water because ion-dipole attractions are strong enough to overcome the crystal lattice energy of the ionic solid salt.

Energy Changes in Solution

separation of solute(absorb = endothermic)

separation of solvent(absorb = endothermic)

attractions between solute and solvent(release = exothermic)

H

Demo

+

+ +

+

+–

–

–

enthalpy(heat)

∆H(final – initial)

Why Do Endothermic

Processes Occur?

Usually favorable processes tend to lower energy. ∆E = – (exo or release)

But in some processes, heat is absorbed, not released.

+

+

+

–

How?

EntropyEntropy (S):

∆S = (final – initial)

∆S = (more – less)

∆S = +

• increasing the entropy (dispersal) by mixing lowers the energy of a system (even if ∆H = +).

(less disorder) (more disorder)

∆H + (heat absorbed)

25oC 25oC 10oC∆E + (raised)

∆S + (gains disorder)

∆E – (lowered)

(disorder or randomness)dispersal of matter & energy

Types of Solutions

• SaturatedSolvent holds

maximum solute possible at that temperature.

Dissolved solute is in dynamic equilibrium with solid solute particles.

• UnsaturatedLess than the

maximum dissolved at that temperature.

Types of Solutions

• SupersaturatedMore solute than is normally possible

at that temperature.unstable; crystallization is stimulated

by a “seed crystal” or scratching.

Types of Solutions

Factors Affecting Solubility

• “like dissolves like”: (similar IMAFs)

Polar substances dissolve in polar solvents.

H2O CH3Cl CH3CH2OH NH3

Nonpolar dissolve in nonpolar solvents.

C6H14 CCl4 I2

similar IMAFs are more soluble.

Which is more soluble in water (H2O) and which is more soluble in hexane (C6H14)

HW p. 566 #12,14,18

Gases in Solution

• In general, the solubility of gases in water increases with increasing size. …WHY?

• Larger molecules have larger e– clouds stronger dispersion forces.

Gases in Solution• The solubility of gas in liquid is

directly proportional to pressure.

Gases are more soluble:

Low THigh P

1) Highest solubility at 20oC? 30oC?

solubility of solids inc. with temp.Solubility

Curves

HW p. 566 #20,23,25

2) How many grams KClO3 at 70oC ?

3) Is 50 g of KCl at 50oC sat, unsat, or supersat?

30 g of NaCl at 30oC?

The greater the IMAFs,…

the _______ the bp and mp.

the _______ the cohesion/adhesion.

the _______ the surface tension.

the _______ the viscosity.

the _______ the vapor pressure (volatility)

Intermolecular Forces Affect Many Physical Properties

greater

greater

greater

greater

lower

Which has a higher boiling point? Explain.

CF4 vs. CH3OCH3

CF4 has London dispersion forces and

CH3OCH3 has dipole-dipole interactions.

Stronger intermolecular attractive forces in

CH3OCH3 require more energy to overcome.

Intermolecular Forces Affect Many Physical Properties

Attractions

Intra–(strong)

Ionic(metal–

nonmetal)

Covalent(nonmetals)

polar non-polar

Inter–(weak)

London dispersion

forces(all, nonpolar)

dipole–dipole(polar)

H–bondsH with N, O, F

ion–dipole(aq ions)

“Bonds” “IMAFs”

mp’s & bp’smp’s (of solids)

4 Types of SolidsIonic [metal–nonmetal]

• ions (transferred e–’s)

Covalent [nonmetals]• sharing of e–’s

Covalent Network [C(d)]• shares e–’s throughout

Metallic [metals]• metal atoms bonded

by a sea of e–’s

Diamond

Quartz

Ionic Solids

• Strong Ionic Bonds in a crystal lattice of +/– ions bonded by electrostatic attraction.

hard and brittlehigh melting pointsconduct in solution(aq) or molten(l)

(Coulombic)

(ordered)

E = q1q2

d

stronger attraction

more q

less d

more energy

to break

Covalent (Molecular) Solids

• Weak IMAF’s (LDF’s, dipole-dipole, H-bonds)softerlower melting points

C(graphite)

Covalent-Network Solids

• Strong Covalent Bonds throughout.C(diamond) WC2 (carbide) SiO2 (quartz)

Very hardVery high melting points

C(graphite) C(diamond)

Metallic Solids• Metals are not

covalently bonded, but attractions are too strong to be IMAFs.

• Metallic Bondsdelocalized valence “sea” of electrons.Excellent conductorsMalleable and Ductile (“smooshable”)soft to very hardlow to very high m.p.’s

Alloys

Alloys:Homogeneous metallic mixtures (solutions) by mixing melted metals in the liquid phase.

Brass Steel

67%Cu, 33%Zn80%Fe, 0.4%C, 18%Cr, 1%Ni

Attractions:Held together mainly by metallic bonding due to a delocalized sea of electrons.

AlloysBrass Steel

• at. radius = similar• density = in between• malleability = similar

Substitutional:• at. radius = different

(smaller fits between larger)

• density = greater(more mass in same volume)

• malleability = less

Interstitial:

Fe Fe Fe Fe

Fe Fe Fe

Fe Fe Fe Fe

C

Attractions in Solids, Liquids, & Solutions

Molecular

Covalent-Network

Ionic

Metallic Metallic Bonds“sea” of electrons

SoftLow mp & bpPoor conductor

Very hardVery high mpPoor conductor

Hard and brittleHigh mpConducts as (aq) or (l)

Soft to very hard Low to very high mp

Great Conductor, Malleable, Ductile

Ar I2 CO2 H2O C2H5OH

C11H22O11C(diamond)

SiO2

WC2

NaClCuSO4

All metals& alloys: Cu, Fe, K, Al,…

Covalent Bonds (network)C(diamond) , SiO2 (quartz) ,WC2 (tungsten carbide) , etc…Ionic Bondscrystal lattice of charged ions

Intermolecular Attractions (IMAFs)London dispersion forcesDipole-dipole interactionsHydrogen bonds

Type Forces Between Particles Properties

d-

d+

- +

Solutions Solute-Solvent Attractionssimilar IMAFs or ion–dipole

(l) + (l),(s) + (l) = (aq)

q1q2

d

(nonpolar)(polar)

(H with N, O, F)

Molecular (IMAFs)

Hydrogen bonds(if H with N , O , or F)

Dipole-dipole interactions(polar molecules)

London dispersion forces(all molecules & nonpolar)instant/induced dipoles)

Ionic Bonds(attractions between +/– ions)

Attraction or Bond Stronger with:

greater ∆ENN < O < F

greater ∆ENgreater dipole moment

larger e– cloud,more polarizable

greater q, less d(Coulombic attraction)

Molecular (IMAFs)

The Stronger the Attractions, the…

higher mp of solid.

harder solid.

higher bp of liquid.

higher viscosity of liquid.

lower vapor pressure of liquid (more volatile).

more soluble in solutions (similar attractions).

Attractions Affect Physical Properties

Reasoning with Concepts

1) Identify attractions(Bonds? IMAFs?)

2)Compare strength

3)Connect to energy (abs./rel.)and/or physical property

+ –