Intermolecular Attractions & the Properties of Liquids & Solids

CHAPTER 12 Chemistry: The Molecular Nature of Matter, 6th edition

By Jesperson, Brady, & Hyslop

REVIEW

2Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

Strength of Intermolecular Forces

CHAPTER 12 Concept Review

London Dispersion Forces

Dipole-Dipole Forces

Hydrogen Bonds (a type of Dipole-Dipole Force)

Ion-Dipole or Ion-Induced Dipole Forces

Weakest

Strongest

3Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

Strength of Intermolecular Forces

CHAPTER 12 Concept Review

London Dispersion Forces: minimized surface area

London Dispersion Forces: maximized surface area

Dipole-Dipole Forces: small overall dipole moment

Dipole-Dipole Forces: large overall dipole moment

Hydrogen Bonds: with 1 H-bond per molecule

Hydrogen Bonds: with multiple H-bonds per molecule

Ion-Dipole or Ion-Induced Dipole Forces

Weakest

Strongest

4Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

Strength of Intermolecular Forces

CHAPTER 12 Concept Review

Property of s, l, g Increases Decreases Example

Boiling Point

Melting Point

Compressibility

Diffusion

Retention of V & Shape

Surface Tension

Wetting

Viscosity

Property of s, l, g Increases Decreases Example

Boiling Point increasing total intermolecular forces

decreasing total intermolecular forces

Water has a high boiling point because it has H-bonding, dipole, and dispersion forces. It is close to heptane (C7H16), a heavier molecule that only experiences dispersion forces .

Melting Point increasing total intermolecular forces

decreasing total intermolecular forces

The melting point of ionic solids is extremely high compared to water which experiences all other intermolecular forces, but not ion-dipole forces. (NaCl is 1074 K and water is 273 K)

Compressibilityincreasing distance between collisions with other particles

decreasing distance between collisions with other particles

Gases are very compressible because the particles have higher kinetic energies, and great distances between particles.

Diffusionwith increasing kinetic energy & increased distance between collisions

with deceasing kinetic energy & decreased distance between collisions

Diffusion is much slower in a solid or in a liquid and much faster in a gas.

Retention of V & Shape

Increasing intermolecular forces and decreasing T & P

Decreasing intermolecular forces, and increasing kinetic energy of particles or T & P

Gases will fill the volume and shape of the container that holds them, while solids will retain their own shape and volume regardless of the container.

Surface Tension with increasing intermolecular forces

with decreasing intermolecular forces

The molecules on the surface have less neighbors (and therefore less stabilizing intermolecular forces) and so have a higher potential energy, which the material will try to reduce with its shape (sphere): water beading.

Wettingwhen there are fewer intermolecular attractions to overcome in order to interact with the surface

When the intermolecular forces in the liquid are stronger then the intermolecular forces with the surface

Water beads on a greasy surface rather then wetting because the dipole forces and hydrogen bonds are so much stronger then the dispersion forces that water experiences with the surface. If the surface is clean it can experience dipole forces and hydrogen bonds with the oxygen in SiO2.

Viscosityincreasing intermolecular forces and decreasing temperature

decreasing intermolecular forces and decreasing temperature

Not just a property of liquids, also gases and solids. Amorphous solids change shape over time because of their viscosity.

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Phase Changes = changes of physical state with temperature ( α to KE)

SOLID LIQUIDGAS

fusion

freezing

evaporation

condensation

deposition

sublimation

endothermic

exothermic

System absorbs energy from surrounds in the form of heato Requires the addition of heat

System releases energy into surrounds in the form of heat or lighto Requires heat to be decreased

TEM

PERA

TURE

HEAT ADDED

HEATING CURVE

solid

liquid

gas

s <--> l

l <--> g

fusionΔHfus

evaporationor vaporization

ΔHvap

endothermic

endothermic

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Equilibrium & Phase Diagrams

T1 = 78°CP1 = 330 atm

To increaseT2 = 100°CThe system must respond by increasing P2 = 760 to restore equilibrium:o T is highero Volume of liquid is

lower o P of vapor higher

Le Chatelier’s PrincipleLiquid + Heat Vapor

If you increase either the liquid or the heat the reaction is

driven to the right to re-establish equilibrium.

If you increase vapor the reaction will be driven to the

left to re-establish equilibrium.

Liquid + Heat Vapor

Liquid + Heat Vapor

Liquid + Heat VaporLiquid + Heat Vapor

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3-D Simple Cubic Lattice

Portion of lattice—open view

Unit Cell

Space filling model

Other Cubic Lattices

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Face Centered Cubic

Body Centered Cubic

Site Counts as Shared by X unit cells

Body 1 1

Face 1/2 2

Edge 1/4 4

Corner 1/8 8

Counting Atoms in Unit Cells

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Interpreting Diffraction DataBragg Equation• nλ=2d sinθ

– n = integer (1, 2, …)– = wavelength of

X rays– d = interplane spacing

in crystal– = angle of incidence

and angle of reflectance of X rays to various crystal planes

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Example: Using Diffraction DataX-ray diffraction measurements reveal that copper crystallizes with a face-centered cubic lattice in which the unit cell length is 362 pm. What is the radius of a copper atom expressed in picometers?

This is basically a geometry problem.

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Ex. Using Diffraction Data (cont.)

diagonal = 4 rCu = 512 pm

rCu = 128 pm

Pythagorean theorem: a2 + b2 = c2

Where a = b = 362 pm sides and c = diagonal

2a2 = c2 and aac 22 2