Chapter 11: Liquids, Solids, and

Intermolecular Forces

Mrs. Brayfield

11.1: Intermolecular Forces

Intermolecular forces are attractive forces that exist

between all molecules and atoms

The state of matter (solid, liquid, or gas) depends on the

magnitude of these forces

11.2: Molecular Comparison of States

A change in state can be achieved by increasing/decreasing

temperature and/or pressure

*Note: solids can be either have well ordered (crystalline) or no order

(amorphous)

Phase Density Shape Volume Intermolecular

Forces

Gas Low Indefinite Indefinite Low

Liquid High Indefinite Definite Moderate

Solid High Definite Definite High

11.3: Intermolecular Forces

Intermolecular forces

originate from the

interactions between

charges, partial charges,

and temporary charges

Remember Coulomb’s Law:

There are 3 types of

intermolecular attractions

(London) Dispersion Forces

This force is present in ALL molecules and atoms

It is the result of fluctuations in the electron distribution within

molecules or atoms

In any one frame the electrons are not symmetrical

around the atom which results in a temporary dipole

(London) Dispersion Forces

An instantaneous dipole on any one atom will induce an

instantaneous dipole on neighboring atoms, which will

then attract each other

The magnitude of the force depends on how easily the

electrons can move

As the molar mass increases the force also increases

This is because of more electrons around a greater volume (easier to

polarize)

See page 392 for more info.

Dipole-Dipole Forces

These forces exist in all polar molecules

There is a permanent dipole from neighboring molecules that

interact with each other

To determine if a molecule has these forces, just

determine if the molecule is polar!

The polarity of molecules also determines miscibility (the

ability to mix – “like dissolves like”)

Dipole-Dipole Forces Example

Which of the following molecules have dipole-dipole

forces?

CI4

CH3Cl

HCl

Answer: CH3Cl and HCl

Hydrogen Bonding

Is not actually bonding (no transfer or sharing of

electrons)

Polar molecules that contain a very electronegative atom

(F, O, or N) exhibit this force

This is a “super” dipole force

The boiling point increases with molar mass

Hydrogen Bonding Example

Which has the higher boiling point, HF or HCl? Why?

HF because it can form hydrogen bonds which is much

stronger than the dipole forces that HCl forms. The stronger

the intermolecular force, the higher the boiling point.

Summary of Intermolecular Forces

No ion-dipole interactions (see original table)

Homework Problems: #1, 2, 4, 6, 8, 10

11.4: Intermolecular Forces in Action

Surface tension – the energy required to increase the

surface area by a unit amount (liquids only)

Molecules interact with their neighbors so the stronger

the intermolecular attractions the higher the surface

tension:

This is what gives water droplets their circular shape

Viscosity

Viscosity – the resistance of a liquid to flow

It is greater in molecules with stronger intermolecular

attractions because if the molecules are strongly attracted

to one another then they do not flow around each other

as freely

The viscosity of maple syrup is larger than that of water

Viscosity is also temperature dependent (as temperature

increases viscosity decreases)

Capillary action

Capillary action – the ability of a liquid to flow against

gravity up a narrow tube

This results from both the attraction between molecules

(cohesive forces) and the attraction between the

molecules and the surface of the tube (adhesive forces)

The adhesive forces causes the liquid to spread out over the

interior surface of the tube while the cohesive forces cause the

liquid to stay together

When adhesive > cohesive water

When adhesive < cohesive mercury

Homework Problems #12, 15

11.5: Vaporization and Vapor Pressure

Vaporization – the process by which thermal energy

can overcome intermolecular forces and produce a phase

change from a liquid to a gas

Remember that molecules are in constant motion (see picture

on page 401)

Vaporization

Every liquid is vaporizing and condensing at the same

time, but not always at the same rate (which results in

liquids evaporating from a container)

The rate can be affected by 3 things:

The rate will increase with a temperature increase

The rate will increase with increasing surface area

The rate increases with decreasing strength of intermolecular

forces

Liquids that evaporate easily are volatile and those that

do not are called nonvolatile

The Heat of Vaporization

The heat of vaporization (ΔHvap) is the amount of heat

required to vaporize one mole of a liquid to a gas

For example:

The heat of vaporization is positive because the process

requires energy

Heat of Vaporization Example

Calculate the amount of heat (in kJ) required to vaporize

2.58kg of water at its boiling point

Vapor Pressure

Vapor pressure – the pressure of a gas that is in

dynamic equilibrium with its liquid

Weak intermolecular forces results in a volatile substance

which results in a high vapor pressure

High intermolecular forces results in a nonvolatile substance

which results in a low vapor pressure

Vapor Pressure

When the system (in dynamic equilibrium) is disturbed

the system responds to minimize the disturbance and

return to a state of equilibrium

The boiling point of a liquid is the temperature at which

its vapor pressure equals the external pressure

Boiling point DOES change with pressure

Think of the boiling point of water here verses in Colorado

Homework Problems: #18, 19, 22, 24

11.6: Sublimation and Fusion

Sublimation – the phase transition from solid to gas

The opposite is called deposition

This is why foods get freezer burned in the freezer – the

water from the food sublimated and is redeposited on

the surface of the food

The melting point is when the molecules have enough

thermal energy to over the intermolecular forces to turn

from a solid to a liquid (otherwise known as melting or

fusion)

The Heat of Fusion

The heat of fusion (ΔHfus) is the amount of heat

required to melt 1 mole of a solid

For example:

The heat of fusion is positive because the process requires

energy

Heat of Fusion Example

An 8.5g ice cube is placed into 255g of water. Calculate the

temperature change in the water upon the complete melting

of the ice. Assume that all of the energy required to melt the

ice comes from the water.

Homework Problems: #30, 32, 34

11.7: Heating Curve for Water

11.8: Phase Diagrams

A phase diagram is a map of the phase of a substance as a

function of pressure (y-axis) and temperature (x-axis)

Homework Problems: #35, 36, 40

11.9: Water

The high boiling point of water can be explained by its

molecular geometry

Which is _________

Water also has a high specific heat capacity which allows

coastal cities to have small temperature fluctuations

For example San Francisco's temp. fluctuation is ~10°F

Water is also funky because it expands when it freezes

Which is the opposite to most liquids

This is why most living things do not survive freezing

Homework Problems: #41, 42, 44

Bent

11.10 – 11.12

You are not responsible for knowing any material in

sections 10 – 12

Review problems: #66, 71

http://www.youtube.com/watch?v=BqQJPCdmIp8