intermolecular forces. kinetic molecular theory describes the behavior of subatomic particles...

Intermolecular ForcesIntermolecular Forces

Kinetic Molecular TheoryKinetic Molecular Theory

Describes the behavior of subatomic particles• Liquids, solids, and gases are composed of

small particles that have mass. • Particles are in constant, random, rapid motion.• Particles have collisions. • Particles have an avg. KE directly related to

temperature.• The state of a substance at room temperature

depends on the strength of the attractions between its particles.

Definition of IMFDefinition of IMF

Attractive forces between molecules.

Much weaker than chemical bonds within molecules.

Definition of IMFDefinition of IMF

Intramolecular forces:

Covalent Bonding

Much stronger than chemical bonds between atoms.

Examples : nonpolar, polar sharing

Definition of IMFDefinition of IMF

Intermolecular ForcesAttractive forces between molecules.

Much weaker than chemical bonds within molecules.

Intermolecular ForcesIntermolecular Forces

Attractive forces between molecules or particles (ions, metal atoms, etc…)

Examples:

dispersion, (London /Vander Waals); dipole-dipole, dipole-ion, hydrogen “bonding”, metallic bonding, ion-ion

Intermolecular ForcesIntermolecular Forces

Relative Strength:

Examples:

dispersion, (London /Vander Waals); dipole-dipole, dipole-ion, hydrogen “bonding”, metallic bonding, ion-ion

Weakest

Strongest

Types of IMFTypes of IMF

Types of IMFTypes of IMF

London Dispersion Forces

View animation online.

Types of IMFTypes of IMF

Dipole-Dipole Forces

+ -

View animation online.

Types of IMFTypes of IMF

Hydrogen Bonding

Determining IMFDetermining IMF

NCl3• polar = dispersion, dipole-dipole

CH4

• nonpolar = dispersionHF

• H-F bond = dispersion, dipole-dipole, hydrogen bonding

Physical PropertiesPhysical Properties

Liquids & SolidsLiquids & SolidsLiquids & SolidsLiquids & Solids

Liquids vs. SolidsLiquids vs. Solids

LIQUIDS

Stronger than in gases

Y

high

N

slower than in gases

SOLIDS

Very strong

N

high

N

extremely slow

IMF Strength

Fluid

Density

Compressible

Diffusion

Liquid PropertiesLiquid Properties

Surface Tension• attractive force between particles in a

liquid that minimizes surface area

Liquid PropertiesLiquid Properties

Capillary Action• attractive force between the surface of

a liquid and the surface of a solid

water mercury

Types of SolidsTypes of Solids

Crystalline - repeating geometric pattern• covalent network• metallic• ionic• covalent molecular

Amorphous - no geometric pattern

decreasingm.p.

Types of SolidsTypes of Solids

Ionic(NaCl)

Metallic

Types of SolidsTypes of Solids

CovalentMolecular

(H2O)

CovalentNetwork

(SiO2 - quartz)

Amorphous(SiO2 - glass)

Liquids & SolidsLiquids & SolidsLiquids & SolidsLiquids & Solids

Changes of StateChanges of State

Phase ChangesPhase Changes

Phase ChangesPhase Changes

EvaporationEvaporation• molecules at the surface gain enough

energy to overcome IMF

VolatilityVolatility• measure of evaporation rate• depends on temp & IMF

Phase ChangesPhase Changes

Kinetic Energy

# o

f P

art

icle

s

p. 477

Boltzmann Distribution

temp

volatility

IMF

volatility

Phase ChangesPhase Changes

EquilibriumEquilibrium• trapped molecules reach a balance

between evaporation & condensation

Phase ChangesPhase Changes

Vapor PressureVapor Pressure• pressure of vapor above

a liquid at equilibrium

IMF v.p.temp v.p.

• depends on temp & IMF• directly related to volatility

p.478

temp

v.p

.

Phase ChangesPhase Changes

Boiling Point• temp at which v.p. of liquid

equals external pressure

IMF b.p.Patm b.p.

• depends on Patm & IMF

• Normal B.P. - b.p. at 1 atm

Which has a higher m.p.?• polar or nonpolar?• covalent or ionic?

Phase ChangesPhase Changes

Melting Point• equal to freezing point

polar

ionic

IMF m.p.

Phase ChangesPhase Changes

Sublimation

• solid gas

• v.p. of solid equals external pressure

EX: dry ice, mothballs, solid air fresheners

Heating CurvesHeating Curves

Melting - PE

Solid - KE

Liquid - KE

Boiling - PE

Gas - KE

Heating CurvesHeating Curves

Temperature Change• change in KE (molecular motion) • depends on heat capacity

Heat Capacity• energy required to raise the temp of 1

gram of a substance by 1°C• “Volcano” clip - water has a very high

heat capacity

Heating CurvesHeating Curves

Phase Change• change in PE (molecular arrangement)• temp remains constant

Heat of Fusion (Hfus)

• energy required to melt 1 gram of a substance at its m.p.

Heating CurvesHeating Curves

Heat of Vaporization (Hvap)

• energy required to boil 1 gram of a substance at its b.p.

• usually larger than Hfus…why?

EX: sweating, steam burns, the drinking bird

Phase DiagramsPhase Diagrams

Show the phases of a substance at different temps and pressures.