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 <ul><li>describe the properties of groups of materials in terms of density, strength, hardness, flexibility, electrical conductivity, thermal conductivity, melting point and boiling point </li></ul><ul><li>distinguish between the main classes of materials (metals, glass, ceramics, plastics and fibres in terms of their properties </li></ul><ul><li>classify a number of common everyday objects and recognise that there are many ways of classifying the same groups of objects </li></ul>
<ul><li>use data on the properties of different materials to make evaluative judgements about their uses </li></ul><ul><li>communicate your findings on classification and justify your reasons </li></ul><ul><li>show an appreciation of Man’s responsibility to have care and concern for the environment </li></ul><ul><li>value individual effort and working in a team as part of scientific inquiry </li></ul>
5.1 Different Ways of Classifying Matter <ul><li>A set is a group of objects with similar properties </li></ul><ul><li>Classification is the grouping of objects into sets according to one or more common properties </li></ul>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 Materials Matter that is used for making objects Chosen 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
Density <ul><li>different materials different densities </li></ul><ul><li>density of a material = characteristic physical property of that material </li></ul>Strength Strength = ability to support a heavy load without breaking <ul><li>Pure metals can be made stronger by forming alloys </li></ul>Combining metals with other metals or non-metals e.g. steel (combination of iron & carbon) is a strong metal <ul><li>Examples of strong materials : fibre glass and concrete </li></ul>A B Which block do you think is more likely to be plastic, and which is more likely to be gold?
Hardness Hardness = ability to withstand scratches and wear <ul><li>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. </li></ul><ul><li>Examples of hard materials : titanium and diamond </li></ul>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
Flexibility The material that bends the greatest distance with the same weight = greatest flexibility Flexibility = ability to bend without breaking Electrical Conductivity <ul><li>Electrical conductivity = measure of how readily an electric current flows through the material </li></ul>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 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 Melting point = Temperature at which substance changes from solid to liquid <ul><li>Melting point = characteristic physical property </li></ul>Melting point of ice is 0°C = ice changes into water at 0°C Melting points of metals are usually very high. Boiling Point Boiling point = Temperature at which substance changes from liquid to gas <ul><li>Boiling point = characteristic physical property </li></ul>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? NO YES Can be spun into thread and woven into cloths? YES fibre NO Brittle? YES Opaque? NO NO YES Can 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 YES
<ul><li>There is actually a specialised field of study called materials science or materials engineering ! </li></ul><ul><li>Scientists and engineers study the structures of materials and their properties and then use their knowledge to create new materials with the desired characteristics. </li></ul>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