Solids, liquids and gases

Transcription

1 Solids, liquids and gases Everything is made up of tiny particles called atoms. Normally, atoms join together to form groups called molecules. Molecules are always moving, even in things that look like they are completely still. Whether something is a solid, a liquid or a gas depends on how much its molecules are moving around. Solids The molecules in solids are packed very tightly together in fixed positions. This makes it difficult for the solid to change shape. Examples: Wood, paper, plastic, metal, glass. Liquids The molecules in liquids are close together, but they are able to slide past one another and change places. This means that liquids can easily change shape. Examples: Rain, lemon juice, milk, blood. IMAGES SCHOLASTIC LTD 2009; WORDS KAREN HART Gases The molecules in gases are spaced widely apart meaning that they can fit into different shapes and be squashed very easily. Examples: Water vapour, oxygen, helium. PHOTOCOPIABLE 1

2 Changes of state A substance changes from one state of matter to another, depending on changes in temperature and pressure. When a substance changes state, heat is either created or lost as the energy of its particles is increased or decreased. Different substances change state at different temperatures. Melting and boiling When a solid is heated, its temperature rises and its particles gain energy. They keep on gaining more energy until they reach their melting point. Once they have reached their melting point, they have enough energy to break away from their neighbours and the solid melts. If a liquid keeps heating up, it will get hotter and hotter until it reaches its boiling point. Now the particles can break free of each other completely and the liquid turns into a gas. This is called evaporation. ICE CUBES FATMAN73/ CONDENSATION HYDROMET/ TEA SCOL22/ Freezing When a liquid cools down enough, it freezes and becomes a solid. This is because its particles lose energy and are pulled towards their neighbours. Most liquids shrink and take up less space when they freeze and turn into a solid, but water does not behave in this way when it freezes, it gets bigger! Condensation When a gas cools down enough, it condenses meaning that it becomes a liquid. This is because, as it cools down, its particles lose energy and can no longer stay as far away from each other. If you breathe onto a cool piece of glass, condensation will appear. The water vapour in your breath condenses when it hits the cool glass and becomes water. PHOTOCOPIABLE 2

3 Materials quiz Cut out the cards below and use them to play your own materials quiz. Describe the material on your card to your team mates (without mentioning it by name) and see if they can guess what you are talking about. Ice Sugar Sand Oxygen Wood Chocolate Rain Leather Air Salt Glass Blood Sawdust Ink WORDS KAREN HART Stone Water vapour PHOTOCOPIABLE 3

4 Materials quiz (cont...) Rubber Syrup Jelly Milk Brick Helium Feather Paper Lemonade Paint Coal Plastic Vinegar Petrol WORDS KAREN HART PHOTOCOPIABLE 4

5 Some common materials Metals All metals (except mercury) are solid at room temperature (20 C) and they are all good conductors of electricity and heat that is, they let electricity and heat pass through them. They are also shiny when they are cut, and some, like iron, are magnetic. Alloys An alloy is a mixture of two or more metals, or a metal and another substance. Alloys are made because they combine the useful bits (like strength and lightness) of the different metals that make them up. Water Water is the most common of all liquids and is found in lots of substances the human body is made up of about 70 per cent water. Water is good at changing its state and then changing back again. It can be a liquid (water), a solid (ice) or a gas (water vapour). Hydrogen Hydrogen is the lightest gas in the whole universe. The Sun and the stars are partly made of hydrogen gas, but on Earth, hydrogen does not occur naturally. Carbon Carbon is a solid and is found in all living things. It can be found mainly in the form of hard, colourless diamond and crumbly black graphite (used to make pencil lead). WORDS KAREN HART Air Air is made up of a number of different gases, approximately 21 per cent oxygen and 78 per cent nitrogen, as well as little bits of other gases. The actual formula is not known because it changes, but it also contains some carbon dioxide and argon. PHOTOCOPIABLE 5

6 The picnic disaster Here are some suggestions for materials that you might like to include in your role play. See if you can think up some good ones of your own to include as well. Do you think a change in temperature is often the cause of a material changing state? Ice cream Melts easily, even in a cool box. Perhaps Dad fetches some ice creams from an ice-cream van, but they melt before he gets back and just the cones are left. Butter Also starts to melt at high temperatures. Would this stay firm and fresh in the sunshine? Water Maybe Dad boiled some water for a cup of tea on a camping stove. What would happen to the water if he forgot about it and left it boiling for too long? Newspaper Did the family bring a mini barbecue? What might happen if Mum carelessly put his newspaper down on top of the hot grill? Bread What would happen if one of the children left a loaf on top of the barbecue, not realising that it was lit? What would it turn into? Ice cubes If Mum brought along a big bag of ice cubes and left it out in the Sun, what would the family find when they went to the bag later on? ILLUSTRATION SIMON WALMESLEY; WORDS KAREN HART PHOTOCOPIABLE 6