Slides - Unit 1

Unit 1

States of Matter

1.1
Everything is Made of Particles

Learning objectives:
■ State that everything is made of particles.
■ Differentiate the atom, molecule and ion.
■ Explain what Brownian motion is.
■ Gives examples of Brownian motion.

Particles:

1. Everything in the universe is made of matter and energy.
2. Matter is defined as anything has mass and occupies space.
3. The particle theory states that all matter is made up of tiny and

discrete particles.
4. The particles can be single atom, molecules or ions.

Particles - Atoms:

1. An atom is the smallest particle of an element that is involved in
a chemical reaction.

2. Atoms have unique names and symbols.

Particles - Molecules:

1. A molecule consists of two or more of the same or different
types of atoms which are chemically bonded together.

2. The atoms in a molecule can be of the same elements or of
different elements.

3. Examples:
i. chlorine gas - Cl2 (molecular element)
ii. water - H2O (molecular compound)
iii. sulfur dioxide - SO2 (molecular compound)

Particles - Ions:

1. An ion is formed when an atom gains or loses one or more
electrons.

2. When an atom gains one or more electrons, it forms a negative
ion (anion).

3. When an atom loses (or releases) one or more electrons, it forms
a positive ion (cation).

1.2
Solids, Liquids and Gases

Learning objectives:

■ Name the three states of matter, and give their physical
properties.

■ Define the terms melt, boil, evaporate, condense,
sublimation.

■ Sketch and label a heating curve and cooling curve.

1.3
The Particles in Solids, Liquids and Gases

Learning objectives:
■ Describe how a substance changes state when heating
using the idea of particles and their movement.
■ Explain the terms melting point, boiling point and
freezing point.

Solids, Liquids and Gases

1. There are three states of matter:

Solid Liquid Gas

2. Matter has different properties in these three states.

Particle separation Solid Liquid Gas
Still close together Far apart
Arrangement of Very close together
particles Irregular pattern Randomly
Regular pattern
Movement of (lattice) Move around, and Free to move at high
particles
Vibrate and rotate slide past each other speeds
Attractive forces about fixed position
between particles Relatively strong Very weak
Very strong (or non-existent)
Compressibility
Cannot be Cannot be Can be compressed
Kinetic energy of compressed compressed
particles
Low Medium High

Change in the States of Matter:

Sublimation: Evaporation:
The change in state directly from solid to The change in state from a liquid to a gas
gas or gas to solid without the liquid below the boiling point of the liquid.
state being formed.

Water:

1. Water can be a solid (ice), a liquid (water), and a gas (water
vapour or steam).

2. Its state can be changed by heating or cooling.
Example: Heating of ice

Explanation for Heating of a Solid (e.g. ice):

Solid → Liquid
i. In a solid, the particles are held in a fixed pattern or lattice. They

don’t move away, but they do vibrate to and fro.

Solid → Liquid

ii. As the particles take in heat energy, the vibrations get larger
and stronger. So the solid expands a little.

Solid → Liquid

iii. With more heat supplied, the particles gain enough energy to
overcome strong attractive force between particles. They
move out of their fixed pattern and can slide over each other.
The solid melts to a liquid.

Liquid → Gas

i. The particles continue to take in heat energy. So they move
around more. They collide into each other more often, and
bounce further apart. So the liquid expands a little.

Liquid → Gas

ii. Some particles gain enough energy to overcome the attractive
forces between them, and escape. This is evaporation.

Liquid → Gas

iii. At a certain point (boiling point), all the remaining particles
gain enough energy to escape. The liquid boils to a gas.

How Much Heat is Needed?

1. The amount of heat needed to melt or boil a substance is different
for every substance.

2. This is because the particles in each substance are holding by
different attractive forces.

3. The stronger the attractive forces between particles, the more
heat energy is needed to overcome them. So the higher the
melting and boiling points will be.

Reversing the Changes:

Those changes of state can be reversed by cooling.
Example: Gas → Liquid → Solid
i. As a gas cools, its particles lose energy and move more slowly.

ii. When they collide, they do not have enough energy to bounce
away. So they stay close, and form a liquid.

iii. On further cooling, the liquid turns to a solid.

Heating curve:

The heating curve shows what happens when we apply steady
heat to a block of ice:

Temperature (oC)

100

water
boiling

0
ice

melting

Time (minutes)

■ A to B: ice warming up
F

■ B to C: ice melting to water

Temperature (oC) 100 DE ■ C to D: water warming up (and
0 some evaporating)

A water ■ D to E: water boiling to water
boiling vapour (or steam)

BC ■ E to F: water vapour getting
hotter
ice
melting

Time (minutes)

■ A to B: Input of energy increase the temperature of ice.

■ B to C: The energy is being used to overcome part of the attractive force between the
particles in the ice. Ice is melting to water. The energy does not go in to raise the
temperature.

■ C to D: The energy increases the temperaure of the water.

■ D to E: The energy is being used to overcome the attractive force between the
particles in the water. Water is boiling to water vapour (or steam). The energy does not
go in to raise the temperature.

■ E to F: The energy increases the temperature of the water vapour.

F

Temperature (oC) 100 D E

water Time (minutes)
boiling

BC

0
ice

melting

A

The temperature stays steady at 0 oC (the
melting point) until all the ice has melted.

F

Temperature (oC) 100 DE
0
water The temperature stays steady
A boiling at 100 oC (the boiling point)
until all the water has turned
BC
to water vapour.
ice
melting

Time (minutes)

Temperature (oC) 100 Summary: ■ A to B: solid
0 ■ B to C: solid and liquid
F ■ C to D: liquid (and gas)
A ■ D to E: liquid and gas
DE ■ E to F: gas

water
boiling

BC

ice
melting

Time (minutes)

Temperature (oC) F

DE

boiling

BC

melting

Time (minutes)

A
The temperature stays steady at the melting point:

■ Heat energy absorbed by the particles is used to overcome part of the attractive
forces between particles.

Temperature (oC) F

DE

boiling

BC

melting

Time (minutes)

A
The temperature stays steady at the boiling point:

■ Heat energy absorbed by the particles is used to overcome the attractive forces
between particles.

Cooling curve:

1. Sketch the cooling curve of water. Explain it.
2. Mark in the condensation and freezing points on your sketch.

Cooling curve:

Temperature (oC) ■ A to B: water vapour
cooling down
A Gas
■ B to C: water vapour
Condensation point C condensing to water
100 B
Liquid ■ C to D: water cooling
Freezing point 0 E down
D
Solid ■ D to E: water freezes to
form ice
F
■ E to F: ice getting cooler

1.4
A Closer Look at Gases

Learning objectives:

■ Explain why a gas exerts a pressure.
■ Explain why the pressure increases when gas is

heating or compress.
■ Explain what diffusion is and how it happens.
■ Describe an experiment to show that a gas will diffuse

faster than another gas that has heavier particles.
■ Discuss how and why the temperature affects the rate

at which a gas diffuses.

Kinetic Particle Theory:

The kinetic particle theory of matter is based on these important
assumptions:
i. Matter is made up of tiny and discrete particles.
ii. The particles are in constant motion (vibrating or moving) and

colliding with each other.
iii. The gas particles move randomly.

A. Brownian Motion:

1. Brownian motion provides evidence for the kinetic particle theory.

2. In 1827, Robert Brown was studying pollen grains in water,
under a microscope, when he observed some pollen grains
continually jigging around.

water molecule

3. The pollen grains moved around
because they were continually
bombarded by the much
smaller water particles, which
were far too small to be seen
with microscope.

4. Brownian motion is the random movement of visible particles
(e.g. pollen grains) in a suspension caused by unequal random
bombardment of much smaller, invisible particles (e.g. water
particles).

Other Examples of Brownian Motion:

i. Dust particles
Dust particles in still air dance around at a sunlit room.

Dust particles (visible)
being bombarded by the
tiny moving air particles

(invisible).

ii. Smoke particles
The zigzag motion of fine smoke particles in air.

Smoke particles
(visible) being
bombarded by the tiny
moving air particles

(invisible).

B. Diffusion:

1. Diffusion is the random movement of particles from a region of
higher concentration to a region of lower concentration.

2. It occurs when the particles of a substance move through the
space between the particles of another substance.

Evidence for Diffusion:

Evidence 1

When a crystal of purple potassium manganate(Vll) is added into water, the purple
colour spreads through the water.

Explanation:
The potassium manganate(VII) particles leave the crystal. They collide with moving
water particles, and bounce away again.
In this way, they mix and spread through the water. So the purple colour spreads
everywhere.

a crystal of potassium manganate(VII)

Evidence 2

The smell of cooking can travel from the
kitchen all through the house.

Explanation:
A ‘smell’ is due to gas particles from the food.
They collide with the gas particles in air, and
bounce away again.
In this way, they mix and spread through the
air. You can smell them when they reach your
nose.

3. The path a particle takes depends on its collisions.

4. It is much faster in gases than in liquids, because particles move
much faster in gases. So the particles collide with more force,
and have more space to bounce further away.

5. As the temperature rises, particles take in more energy and
move faster. So diffusion is faster too.

Comparing the Rates of Diffusion for Gases:

Gases do not diffuse at the same rate even at the same temperature.
Example:

(release ammonia (release hydrogen chloride
molecules – gas) molecules – gas)

i. Particles of ammonia gas and hydrogen chloride gas diffuse
from the opposite ends of the long glass tube.

(*the particles are molecules.)

ii. When they meet, they combine to form a white cloud of
ammonium chloride.

iii. The white cloud of ammonium chloride forms closer to the
right-hand end. This indicates that the ammonia molecules
have travelled faster. That’s because the ammonia molecules
have a lower relative molecular mass.

(*the relative molecular mass are: ammonia 17; hydrogen chloride 36.5.)

The lower its relative molecular mass,
the faster a gas will diffuse.

C. Gas Pressure:

Recall Year 8 lesson:

i. Gases are made up of tiny and discrete particles.

ii. The particles move randomly and collide with each other, and
with the wall of container.

iii. The colliding particles exert a force on the wall, and push it
outwards.

iv. The force exerted by the gas particles on the surface of wall
known as gas pressure.

Gas Pressure:

1. All gases exert a pressure.

2. The pressure depends on the temperature of the gas and the
volume it takes up.