chapter 131 intermolecular forces: liquids, and solids chapter 13

Chapter 13 1

Intermolecular Forces: Intermolecular Forces: Liquids, and SolidsLiquids, and Solids

Chapter 13Chapter 13

Chapter 13 2

A Molecular Comparison of Liquids A Molecular Comparison of Liquids and Solidsand Solids

Chapter 13 3

Intermolecular ForcesIntermolecular Forces

Chapter 13 4

Intermolecular ForcesIntermolecular Forces

Ion-Dipole ForcesIon-Dipole Forces- Interaction between an ion (Na+) and a dipole (water).- Strongest of all intermolecular forces

Chapter 13 5

Intermolecular ForcesIntermolecular Forces

Chapter 13 6

Intermolecular ForcesIntermolecular Forces

Dipole-Dipole ForcesDipole-Dipole Forces- Interaction between an dipole on one molecule and a

dipole on an adjacent molecule.- Dipole-dipole forces exist between neutral polar

molecules.- Weaker than ion-dipole forces

Chapter 13 7

Intermolecular ForcesIntermolecular Forces

Chapter 13 8

Intermolecular ForcesIntermolecular Forces

London Dispersion ForcesLondon Dispersion ForcesInduced Dipole – Induced DipoleInduced Dipole – Induced Dipole

- Weakest of all intermolecular forces.- It is possible for two adjacent nonpolar molecules to

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

electrons of the adjacent molecule (or atom).- This attraction causes the electron clouds become

distorted.- In that instant a polar molecule (dipole) is formed

(called an instantaneous dipole).

Chapter 13 9

Intermolecular ForcesIntermolecular Forces

London Dispersion ForcesLondon Dispersion Forces

Chapter 13 10

Intermolecular ForcesIntermolecular ForcesHydrogen BondingHydrogen Bonding- A special case of dipole-dipole forces.- This intermolecular force is very strong. - Strongest of the three Van der Waal’s forces

(Hydrogen bonding, Dipole-dipole, London forces,)- H-bonding requires H bonded to an electronegative

element (most important for compounds of F, O, and N).

Chapter 13 11

Intermolecular ForcesIntermolecular ForcesHydrogen BondingHydrogen Bonding

Chapter 13 12

Some Properties of LiquidsSome Properties of Liquids

ViscosityViscosity- Viscosity is the resistance of a liquid to flow.- A liquid flows by sliding molecules over each other.- The stronger the intermolecular forces, the higher the

viscosity.

Chapter 13 13

Some Properties of LiquidsSome Properties of Liquids

Surface TensionSurface Tension- The surface of a liquid behaves as a membrane or

barrier.- This is due to the unequal attractive forces on

molecules as the surface.- Surface molecules are only attracted inwards towards

the bulk molecules.

Chapter 13 14

Some Properties of LiquidsSome Properties of Liquids

Surface TensionSurface Tension- Cohesive forces bind molecules to each other.- Adhesive forces bind molecules to a surface.

Chapter 13 15

Some Properties of LiquidsSome Properties of Liquids

Surface TensionSurface Tension- Meniscus is the shape of the liquid surface. – If adhesive forces are greater than cohesive forces, the

liquid surface is attracted to its container more than the bulk molecules. Therefore, the meniscus is U-shaped (e.g. water in glass).

– If cohesive forces are greater than adhesive forces, the meniscus is curved downwards.

Chapter 13 16

Some Properties of LiquidsSome Properties of Liquids

Surface TensionSurface TensionCapillary Action - When a narrow glass tube is placed in

water, the meniscus pulls the water up the tube.

Chapter 13 17

Properties of LiquidsProperties of LiquidsVaporizationVaporization• Also called evaporation– A process in which a substance is transfromed from a liquid

to a gas.

• Standard molar enthalpy of vaporization (Hovap)

– The energy required to convert one mole of a liquid at its boiling point to a gas.

• The resulting gas will exert a pressure on a system.

Chapter 13 18

Properties of LiquidsProperties of LiquidsVapor PressureVapor Pressure• This is the pressure exerted by a substance in the gas

phase.• As a liquid’s temperature increases, its vapor

pressure increases.

Chapter 13 19

Properties of LiquidsProperties of LiquidsVapor PressureVapor PressureVolatile – A substance which has a low boiling point

Or

A substance which has a high vapor pressure at a low temperature

Chapter 13 20

Properties of LiquidsProperties of LiquidsVapor Pressure and Boiling PointVapor Pressure and Boiling Point- Liquids boil when the external pressure equals the

vapor pressure.- Two ways to get a liquid to boil: increase temperature

or decrease pressure.- Normal boiling point is the boiling point at 760 mmHg

(1 atm).

Chapter 13 21

Properties of LiquidsProperties of LiquidsVapor Pressure and Boiling PointVapor Pressure and Boiling Point- Vapor pressure, temperature and enthalpy of

vaporization can be related to each other using:Clausius-Clapeyron equation:

211

2 11ln

TTR

H

P

Povap

P = pressureT = temperatureR = gas lawHo

vap = enthalpy of vaporization

Chapter 13 22

Properties of LiquidsProperties of LiquidsVapor Pressure and Boiling PointVapor Pressure and Boiling Point

The Clausius-Clapeyron equation makes more sense when it is rearranged into the slope intercept form.

CRT

HP

ovap

ln

Chapter 13 23

Properties of LiquidsProperties of LiquidsVapor Pressure and Boiling PointVapor Pressure and Boiling Point

Chapter 13 24

Structures of SolidsStructures of SolidsUnit CellsUnit Cells- Crystalline solid: well-ordered, definite arrangements

of molecules, atoms or ions. - Crystals have an ordered, repeated structure.- The smallest repeating unit in a crystal is a unit cell.- Three-dimensional stacking of unit cells is the crystal

lattice.

Chapter 13 25

Structures of SolidsStructures of SolidsUnit CellsUnit Cells

Chapter 13 26

Structures of SolidsStructures of SolidsUnit CellsUnit Cells

Chapter 13 27

Structures of SolidsStructures of SolidsCell OccupancyCell Occupancy

Chapter 13 28

Structures of SolidsStructures of SolidsCell OccupancyCell Occupancy

Chapter 13 29

Structures of SolidsStructures of SolidsCell OccupancyCell Occupancy

Site Occupancy

Corner 1/8

Edge 1/4

Face 1/2

Center 1

Chapter 13 30

Structures of SolidsStructures of SolidsCell OccupancyCell Occupancy

Zinc (grey) 4 Center 4 atoms

Sulfur (yellow) 8 corners

6 faces

1 atom

3 atoms

Zn4S4 ZnS

Chapter 13 31

Structures of SolidsStructures of SolidsClose Packing of SpheresClose Packing of Spheres- A crystal is built up by placing close packed layers of

spheres on top of each other.- There is only one place for the second layer of

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

called hexagonal close packing (hcp).

- Third layer is in a different position relative to the first (ABCABC arrangement). This is called cubic close packing (ccp).

Chapter 13 32

Structures of SolidsStructures of SolidsClose Packing of SpheresClose Packing of Spheres

Chapter 13 33

Structures of SolidsStructures of SolidsClose Packing of SpheresClose Packing of Spheres- Each sphere is surrounded by 12 other spheres (6 in

one plane, 3 above and 3 below).- Coordination number: the number of spheres directly

surrounding a central sphere.

Chapter 13 34

Structures of SolidsStructures of SolidsOther Kinds of Solid MaterialsOther Kinds of Solid Materials

Molecular SolidsThese are crystalline substances in which the “building blocks” are composed of molecules in place of ions.

Example: Table Sugar

Chapter 13 35

Structures of SolidsStructures of SolidsOther Kinds of Solid MaterialsOther Kinds of Solid Materials

Network SolidsThese are crystalline substances in which the “building blocks” are atoms and all the atoms are connected by covalent bonds.

Example: Diamond

Chapter 13 36

Phase DiagramsPhase Diagrams- Phase diagram: plot of pressure vs. temperature

summarizing all equilibria between phases.

Chapter 13 37

Phase DiagramsPhase Diagrams

Chapter 13 38

Phase DiagramsPhase DiagramsTriple point - Temperature and pressure at which all

three phases are in equilibrium.

Critical point – Point above which the liquid and gas phases are indistinguishable.

Critical temperature - The minimum temperature for liquefaction of a gas using pressure

Critical pressure - Pressure required for liquefaction

Chapter 13 39

2, 16, 18, 24, 30, 32, 40, 44

HomeworkHomework