Particulate Model of MatterParticulate Model of Matter

22.1 What Matter is Made Up of

• What is matter made up of?

• Ancient Greek philosophers thought that matter was made up of fire, air, earth and water.

• However, scientists today have deduced from experiments that matter is made up of tiny particles that are in constant and random motion.

22.2 Evidence for Moving Particles

• The spreading of smells, such as from cooking or perfumes, is because of the movement of tiny particles in air.

• These particles move about randomly in all directions, and hence the smells spread.

• We say that diffusion has taken place.• Diffusion is a process by which particles of

matter move from a region of higher concentration to a region of lower concentration.

Experiment 1: Diffusion in Gases

Prepare a gas jar of bromine vapour by placing a few drops of liquid bromine in the gas jar. Then invert a gas jar containing air over it. Observe what happens.

After some time, both gas jars become filled uniformly with a reddish-brown colouration.

22.2 Evidence for Moving Particles

22.2 Evidence for Moving Particles

• Diffusion also occurs in liquids.

• However, it takes place more slowly than in gases.

• This shows that particles in a liquid move around more slowly than in gases.

Experiment 2: Diffusion in LiquidsPlace a few crystals of potassium permanganate at the bottom of a beaker of water. Leave the set-up to stand and observe it from time to time.

After a few days, the purple colouration of potassium permanganate will spread throughout the mixture.

22.2 Evidence for Moving Particles

water

potassium permanganate crystals At the

beginningAfter a few days

22.3 Particulate Model of Matter

Property Solids Liquids GasesShape • Have fixed

shapes• Have no fixed

shapes• Take the

shape of their containers

• Have no fixed shape

• Take the shape of their containers

Volume • Have fixed volumes

• Have fixed volumes

• Have no fixed volume

• Fill up the space of their containers

Compressibility • Cannot be compressed

• Cannot be compressed

• Can be compressed

22.3 Particulate Model of Matter

• Scientists use the particulate model of matter to explain that the three states of matter are different because of the differences in the movement (motion) and arrangement of the particles.

• We can use the particulate model to explain why the behaviour of solids, liquids and gases differs form one another.

Particulate model of solids

• The particles in the solid state:o are strongly attracted to each othero are packed very closely togethero are arranged in a fixed, regular pattern; and o can only vibrate about their fixed positions.

Particulate model of solids

• The particles in a solid are unable to move freely. Thus, a solid has a definite shape and volume.

• There is no space between the particles to enable them to get any closer to one another. This is why solids cannot be compressed.

Particulate model of liquids

• The particles in the liquid state:o are attracted to one another;o are packed closely together;o are not arranged in a fixed, regular pattern; and o can move over short distances.

Particulate model of liquids

• The particles in the liquid state are farther away from one another than the particles in a solid.

• However, the particles in a liquid are still held closely together.

• Thus, like solids, liquids have a fixed volume and cannot be compressed.

• Unlike solids, the particles in a liquid are not fixed in regular positions and are able to slide past one another. This is why a liquid has no definite shape.

Particulate model of gases

• The particles in the gaseous state:o are weakly attracted to one anothero are far apart from one another; ando can move freely in any direction.

Particulate model of gases

• The particles in a gas are spaced far apart from one another and so a gas can be compressed easily.

• The particles are also able to move freely to occupy any available space.

• This explains why a gas has no definite shape or volume.

22.4 Changes of States of Matter

• Matter can exist in the solid, liquid or gaseous state, depending on its temperature and atmospheric pressure.

• At a fixed pressure, the temperature of an object will determine its state.

Boiling occurs when ice is heated to a temperature of 0 0C and above.

Boiling occurs when liquid water is heated to a temperature of 100 0C.

Freezing occurs when water is cooled to 0 0C and below.

Condensation occurs when water vapour is cooled to a temperature of 100 0C and below.

Melting

• When a solid is strongly heated, the particles gain energy and vibrate more vigorously in their fixed positions.

• When the particles have enough energy (i.e. reach the melting point), they break free from one another and move about randomly.

• The particles are no longer held in fixed positions, but they are still close to one another.

• This change in arrangement and motion of particles is known as melting.

Solid LiquidGain in energy

Freezing

• When a liquid is cooled, the particles lose energy and they move about more slowly.

• As the temperature falls, the particles lose more and more energy until they are close enough to allow the forces of attraction to make them return to their fixed positions.

• The substance has changed from a liquid to a solid.• This change in arrangement and motion of particles is

called freezing.

Liquid Solid

Loss in energy

Boiling• When a liquid is heated, the particles gain energy

and vibrate and move about more vigorously. • When the particles have enough energy (i.e reach

the boiling point), they break free from one another.

• The particles become randomly arranged, very far apart and moving about at great speeds.

• This change in arrangement and motion of the particles is known as boiling.

Liquid GasGain in energy

Condensation

• When a gas is cooled, the particles lose energy and they move about less vigorously and at lower speeds.

• As the temperature falls, the particles lose more and more energy until they are close enough to be attracted to one another.

• The substance has turned from a gas to a liquid.• This change in arrangement and motion of particles is

known as condensation.

Gas Liquid

Loss in energy

Miscellaneous

• http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/particle_model_intro.shtml

• http://www.chem4kids.com/files/matter_intro.html

• http://www.abpischools.org.uk/resources/solids-liquids-gases/slg2.asp

• http://www.chem.purdue.edu/gchelp/liquids/character.html