11

Chapter 12: Liquids, Solids and Interparticle Forces

22

What is a liquid? A solid?

Properties of liquids and solids: depend on Interparticle (Intermolecular) forces- vaporization/condensation/freezing- equilibrium vapor pressure/volatility- surface tension- boiling point/freezing point

We are going to learn about Interparticle or Intermolecular forces first!

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TYPES OF INTERPARTICLE FORCES - SEE HANDOUT

All forces of attraction between atoms, ions, molecules are “Interparticle” forces

Includes ionic bonding, covalent bonding, metallic bonding, and ion-dipole attraction

Important Subcategory is Intermolecular Forces Also called Van Der Waal’s forcesWeak to moderate forces of attractionNot a type of bondingIncludes three main ones: London Dispersion Forces, Dipole-dipole Attraction and Hydrogen Bonding Attraction

44

Intermolecular Forces

1. London dispersion forces (LDF)- Small to moderate strength- Depend on size of electron cloud (and so also molar mass) of atom or molecule- Noble gases, diatomic elements, and many other nonpolar compounds

55

Nonpolar molecules such as H2 can develop instantaneous dipoles and induced dipoles. The attractions between such dipoles, even through they are transitory, create London dispersion forces. (See figures 12.17 & 18)

66

Noble Gas

Molar Mass, (g/mol)

Boiling Point, (K)

He 4.00 4.2

Ne 20.18 27

Ar 39.95 87

Kr 83.80 120

Xe 131.29 165

Table 12.4: Dispersion Force and Molar Mass

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Relationship between Dispersion Force and Molecular Size

-300

-250

-200

-150

-100

-50

0

50

100

150

200

250

1 2 3 4 5 6

Period

Boi

ling

Poi

nt, °

C

BP, Noble Gas

BP, Halogens

BP, XH4

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Intermolecular Forces

2. Dipole-dipole attraction- Moderate strength- Molecules that have polar covalent bonds- Polar molecules + and - attraction

Table of Properties of HydrohalogensH-F H-Cl H-Br H-I

EN 1.4 1.1 0.8 0.4# e-s 10 18 36 54BP 291 188 206 238

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There are many dipole-dipole interactions possible between randomly arranged ClF molecules. In each interaction, the positive end of one molecule is attracted to the negative end of a neighboring ClF molecule.

1010

MolarMass (g/mol)

Boiling Point, °C

Dipole Size, D

CH3CH2CH3 44 -42 0

CH3-O-CH3 46 -24 1.3

CH3 - CH=O 44 20.2 2.7

CH3-CN 41 81.6 3.9

Polarity and Dipole-to-Dipole Attraction

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Intermolecular Forces

3. Hydrogen-bonding (enhanced dipole-dipole)- Strong force, but much less than real bonding- Memory helper: E.T. FON Home: only F-H, O-H and N-H have this type of force- Due to small radius and high EN- See in boiling point data

1212

Depiction of hydrogen bonding among water molecules. The dotted lines are the hydrogen bonds.

1313

Figures 12.22 & 24: Intermolecular H-Bonding

1414

Hydrogen Bonding and Water:Water - 80% hydrogen-bonded - very tight

arrangement (also high viscosity high density and high specific heat)

Ice - crystal is very open, less dense than liquid

(4. Dipole - induced dipole between diff types of molecules, O2 in H2O)

1515

Diagrams of hydrogen bonding involving selected simple molecules. The solid lines represent covalent bonds; the dotted lines represent hydrogen bonds.

1616

If there were no hydrogen bonding between water molecules, the boiling point of water would be approximately - 80C.

1717

Relationship between H-bonding and Intermolecular Attraction

-200

-150

-100

-50

0

50

100

150

1 2 3 4 5

Period

Bo

ilin

Po

int,

°C

BP, HX

BP, H2X

BP, H3X

BP, XH4

CH4

NH3

HF

H2O

SiH4

GeH4

SnH4

H2S H2Se

H2Te

Notice that molecules with F-H, O-H and N-H have HIGH BPs because of Hydrogen-bonding forces of attraction.

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Properties and H-Bonding

NameNameForm-Form-

ulaula

Molar Molar MassMass StructureStructure

BP,BP,

°C°CMP,MP,

°C°C

Sol’b Sol’b in in

WaterWater

EthaneEthane CC22HH66 30.030.0 -88-88 -172-172 immisimmiscc

MethanMethanolol

CHCH33OOHH

32.032.0 64.764.7 -97.8-97.8misc-misc-

bleble

H C

H

H

C H

H

H

H C

H

H

O H

Table on page 411 in Tro.

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Chemistry at a Glance:Intermolecular Forces

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PRACTICE IDENTIFYING THE TYPE OF IM FORCE:

CH4(g) C6H6(l)

Br2(l) HBr(l)

IBr(s) CH3OH(l)

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There are six changes of state possible for substances: learn all 6

2222

Distinguishing Properties of Solids, Liquids, and Gases

2323

BP, FP, Phase Changes, and Ho

phase

Boiling point: temperature at which the vapor pressure of a liquid is equal to the external pressure above the liquid, usually atmospheric pressure of 1 atm

Freezing point: temperature at which a liquid changes into a solid at 1 atm

2424

BP, FP, Phase Changes, and DHo

phase

Phase changes: changes of stateLearn all sixAccompanied by heat flow called

Enthalpy of phase change or Hophase

Heat of vaporization: liquid to vapor; energy (J) to vaporize 1 mol at constant T & P

Heat of fusion: solid to liquid; energy (J) to melt 1 mol at constant T & P

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BP, FP, Phase Changes, and Ho

phase

Sensible heat transfer: temperature is changed but not phase

q = m * cp * Tm is mass, cp is specific heat and T is Tf – Ti

See example (13.1***)Latent heat transfer using Ho

phase: phase changes but not temperature

q = m * Hophase

m is mass or moles depending on unitsSee example (13.2***)

2626

BP, FP, Phase Changes, and Ho

phase

Specific heat: energy required to raise temperature of 1.00 gram of substance by 1.00oC

cp for water is 4.184 J/g.oC

2727

In the evaporation of a liquid in a closed container (a), the liquid level drops for a time (b) and then becomes constant (ceases to drop). At that point a state of equilibrium has been reached in which the rate of evaporation equals the rate of condensation (c).

2828

Equilibrium Vapor Pressure

In closed system: at any given temperature, rate of vaporization = rate of condensation

At dynamic equilibrium: means number of molecules in gas phase and number of molecules in liquid phase stay the same, but processes still happening

Vapor pressure taken at equilibrium = the partial pressureVapor pressure changes with change in temperature

(listen to weather)Plot as vapor pressure curves: pressure vs. temperature

(see Fig 13.6)Boiling point anywhere along curve: see bubbles rise to

surfaceNormal boiling point is when vapor pressure is 1.00 atm or

760. Torr

2929

Vapor Pressure of Water at Various Temperatures.

3030

Boiling Point of Water at Various Locations That Differ in Elevation

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Just read about surface tension and capillary action

Just read section (****13.10 and skip section 13.11