Chapter

5: Classification of

Matter

fibre

Observe the things around you, are you able to identify the different types of matter?

wood

plastic

Lesson Outline

• describe the properties of groups of materials in terms of density, strength, hardness, flexibility, electrical

conductivity, thermal conductivity, melting point and boiling point

• distinguish between the main classes of materials (metals, glass, ceramics, plastics and fibres in terms of their properties

• classify a number of common everyday objects and recognise that there are many ways of classifying the same groups of objects

• use data on the properties of different materials to make evaluative judgements about their uses

• communicate your findings on classification and justify your reasons

• show an appreciation of Man’s responsibility to have care and concern for the environment

• value individual effort and working in a team as part of scientific inquiry

5.1 Different Ways of Classifying Matter

• A set is a group of objects with similar properties

•Classification is the grouping of objects into sets according to one or more common properties

Classifying materials helps us to choose the right materials to make certain products

How are the above objects classified?

5.2 Physical Properties of Materials

MaterialsMatter that is used for making objectsChosen to make objects based on their physical properties

Physical property

Any aspect of an object that can be measured without changing its identity

Includes density, strength, hardness, flexibility, electrical conductivity, thermal conductivity, melting and boiling point

Why are different materials used to make cups?

glass

paper ceramic

• different materials different densities

• density of a material = characteristic physical property of that material

Strength = ability to support a heavy load without breaking• Pure metals can be made stronger by forming alloys Combining metals with

other metals or non-metals

e.g. steel (combination of iron & carbon) is a strong metal

• Examples of strong materials : fibre glass and concrete

A

B

Which block do you think is more likely to be plastic, and which is more likely to be gold?

Hardness = ability to withstand scratches and wear

• Can be determined by a simple scratch test. A material can scratch all materials that are softer than itself but not materials harder than itself.

• Examples of hard materials : titanium and diamond

It is very hard and can only be cut by other diamonds.

Ha! I knew it! You are softer than me!

Alright...

My friends say that I am very strong,

Really? Lets take a test to see who is stronger!

plastic plate

The material that bends the greatest distance with the same weight = greatest flexibility

Flexibility = ability to bend without breaking

• Electrical conductivity = measure of how readily an electric current flows through the material

Electrical conductors Electrical insulators

Allow electric current to flow through them easily (e.g. metal & carbon)

Do not allow a large electric current to flow through them easily (e.g. non-metals)

Thermal conductivity = measure of how readily heat flows through the material

Thermal conductors Thermal insulators

Allow heat to flow through them easily (e.g. metal)

Do not allow heat to flow through them easily (e.g. non-metals & gases)

Example : Almost every part of the kettle is made of stainless steel except for the handle (plastic) because we want heat to be transmitted through the metal quickly to boil water, and the handle to be cool so that we can hold the kettle.

Can you think of other examples?

metal

plastic

Melting point = Temperature at which substance changes from solid to liquid• Melting point = characteristic physical property

Melting point of ice is 0°C = ice changes into water at 0°C

Melting points of metals are usually very high.

Boiling point = Temperature at which substance changes from liquid to gas• Boiling point = characteristic physical property

Boiling point of water is 100°C = water changes into steam at 100°C

Fractional distillation is used to separate the components with different boiling points in a mixture

5.3 Distinguishing Between the Main Classes of Materials

To reduce the amount of materials disposed we need to first understand the properties of different materials.

Scientists have classified materials into five main classes:

metal

plastic

glass

ceramic

fibre

Material

Good conductor of heat?

Good conductor of electricity?

YES NO

YES

Can be spun into thread and woven into cloths?

YESfibre

NO

Brittle?YES

Opaque?

NO

NO YESCan be moulded into different shapes after melting?YES

plastic

glass High melting point?

ceramic

YES

Shiny surfaces?

YES

High melting and boiling points?

Malleable and ductile?

YES

metal

YES

• There is actually a specialised field of study called materials science or materials engineering!

Scientists and engineers study the structures of materials and their properties and then use their knowledge to create new materials with the desired characteristics.

Did You Know???

5.4 Choosing the Right Materials

Why are different materials chosen for different parts of the bulb?

Bulb

Function: give off light

Material: glass

Properties: transparent, electrical insulator

Filament

Function: produce light when heated

Material: tungsten

Properties: electrical conductor, high melting point, ductile, malleable

Connecting and supporting wires

Function: provide support to filament

Material: Tungsten

Properties: Electrical conductor, high melting point, ductile, malleable

Exhaust tube

Function: provide support to filament and connecting wires

Material: Ceramic

Properties: electrical insulator, high melting point, heat insulator, strong

Base

Function: connect bulb to power source

Material: metal

Properties: Electrical conductor, malleable