Post on 14-Jan-2015
description
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