IOP Institute of Physics

# Experiments

Solids: Snowflakes and Bubbles

1. Start by an activity to attract their attention. (Show slide 1)

 Activity Discussion Use a spray bottle to spray water onto a cloth that changes shade of colour when it is wet.Then try to spray using the bottle containing the ice.View Apparatus List Ask them what changes they see. Encourage answers about liquids being able to change shape so is squeezed out of the spray.Ask what is different. Encourage statements about solids not changing shape therefore it is not possible for the ice to be sprayed from the bottle.Aim to find out what they know and to establish the difference between liquids and solids.

2. Use slide 2 to reinforce that solids do not change shape when you move them.

 Activity Discussion The natural object is Stannage Edge in Derbyshire, a natural rock formation.The crown links well with crystals shown later in the presentation. There are numerous different sorts of solids.(Be prepared for questions about paper or springs which are flexible and solid. Solids can be forced to change shape.)Solids have a fixed shape.

3. Show a melted candle or piece of chocolate.

 Activity Discussion View Apparatus ListUse slide 3 to reinforce that liquids have no shape.The atoms in the liquid can move around freely. Talk about atoms being very tiny particles. Ask what happens when they keep chocolate in their pocket on a hot day. Use this to lead into a discussion about melting being the change from a solid to a liquid. (Different solids melt at different temperatures. Ice melts at 0oC, iron at 1535oC.)Liquids take the shape of the container. A solid melts to form a liquid.

4. Tell that solids are amazing because they ‘remember’ how they grew.

 Activity Discussion (Show Slide 4) E.g. as water freezes it can form 2 types of solid –snow/frost and ice. Ask them whether they have seen frost on car windscreens on frosty mornings and icicles etcUse Slides 5 and 6 to encourage the children to recount what they have seen and link the solids with water.The same material can exist as both solid and liquid.

5. Show two glasses of water and explain that one is water from the tap and the other from melted ice.

 Activity Discussion View Apparatus ListAsk whether they can tell the difference. (Slide 7) Discuss how the water in each is formed. The melted ice was solid before it melted. The water from the tap was rain so formed from condensed water vapour.Liquids do not have a memory of how they are formed.

6. Explain that during the session they will learn about two ways solids grow. (Slide 8).

Discussion

 Activity Discussion This is useful because scientists can grow solids atom by atom in special ways to do special tasks.

7. Type 1, Snow flakes (Show PowerPoint slide 9)

 Activity Discussion The atoms add on exactly where they hit. (Slide 10) Talk about the formation of clouds - that water vapour rises and forms clouds. When it is cold the water vapour freezes. Snowflakes grow as water molecules add onto others.Liquids can be changed to a solid by cooling and this is freezing or solidifying.

8. Computer simulation (Slide 11, 12)

9. Type 2, ice

 Activity Discussion (Slide 15) Emphasise that ice is hard.(Slide 16) Explain that this is because of the way the ice was formed from water. Ask whether they have ever jumped on a frozen puddle. Ask what the flakes of ice are like: hard, see-through, sharp edges., flat sides. Ask them if they have ever felt under the ice from a puddle and noticed how very smooth it is. Compare with the pictures of crystals. (Slide 16).Solids formed in this way have very smooth sides and are very hard.

10. (Show PowerPoint slide 17)

 Activity Discussion Explain that the crystals have atoms in layers- that just as they have learned that atoms are very small- the layers are very thin. About 10,000 layers are needed to get the thickness of a piece of paper. They are impressed by the large numbers. Explain that in the large piece of quartz crystal shown there will be 100 million layers!The layers of atoms are very, very thin.

11. (Slides 18 and 19) Growing solids atom by atom artificially.

 Activity Discussion The temperature has to be just correct to get the best structure. A beam of atoms is sprayed onto a surface and they move around to find the closest position. Discuss crystal growing kits (available from toy shops). Ask if they have ever grown crystals - they would have warmed the powder in the water and then leaved it to cool. Explain that just at the temperature where a liquid changes to a solid, the atoms can move around to find the best place so that they are all very close together.Show the BBC clip to show that some VERY big crystals can grow – if you leave them long enough!Different solids melt at different temperatures.

12. On an Overhead projector, show discs being packed as close as possible together.

 Activity Discussion View Apparatus ListExplain that when they are packed closely they form a solid – crystal. (Slide 19).When the discs all touch each near disc- there is only one possible pattern.

13. Class group activity

 Activity Discussion View Apparatus ListHand out about 12 discs per group. Ask them to place them together so that they are as close as possible. Do this on the OHP at the same time. Give them three narrow strips of paper and ask them to place them over the lines they can see. Use Slides 21, 22, 23, 24 to reinforce this. They may suggest other structures but this is the closest packed and known as ‘close packed hexagonal’. Ask if they know the word hexagonal- some may link this with a hexagon. Talk about the six sides and point out that each disc touches six others.Atoms in a solid (crystal) are in a pattern which repeats many, many times.

14. Bubble rafts - (Show PowerPoint Slide 25)

 Activity Discussion View Apparatus ListExplain that we can find out more using bubbles. Go through the instructions with them using Slide 26. Explain that they will need to be very sensible if this is to work because if they do not do it very carefully they will not get the effect. The children will see that the pattern formed by the bubbles is similar to that formed in the previous exercise. They should slide the bubbles around carefully with their fingers to form a large raft. Safety: If they ask can they do it at home, warn them to ask an adult to make the hole in the yogurt pot as it is difficult to push the pin through.The atoms move so that they are packed closely in the pattern. Such solids are hard.

15. Show PowerPoint slide 27 and ask what they can see.

 Activity Discussion Use Slide 28 to emphasise that the bubbles slide around to reach the best place. If a bubble bursts others will move so there is no gap.Use Slides 29 and 30 to show the rows clearly. In the discussion compare with other natural structures. Ask where they have seen similar patterns and show the picture of the honeycomb - if available, take in a piece of honeycomb to show them.(Slide 30).The close packed pattern formed by the atoms occurs many times in nature.

16. Discuss the bubbles. They are not like the soapy water, nor the air. The layers of bubbles could be built up to form a structure that is very different to either the water or the air.

 Activity Discussion Show PowerPoint Slide 32 then the picture of the foam dance. They will mention bubble baths - task if they have been in a jacuzzi in the swimming baths- ask what would happen if bubble bath liquid were to be put into a jacuzzi. This emphasises that the structure of the water is different to that of air or water.

17. Show PowerPoint slide 33. Reinforce that soap films are very thin.

 Activity Discussion A thin film of water is very different from water in a bucket or glass.We have a very thin sandwich‘air- water –air’.The bubbles behave like layers of atoms – which can build a crystal. Talk about foam from soapy water. Bring out in the discussion that the bubbles will build something that cannot be made from just water or just air.The bubbles behave like atoms building a solid.

18. Sandwich crystals can be made with the very special machine. (Slide 35)

 Activity Discussion These have different sorts of atoms in layers. These can do very special jobs.Explain that computer ‘chips’ are made from these very special crystals. ‘Chips’ are used in lots of different items that they use. Ask if they can spot some of them on Slide 35?iPods, games consoles, play stations, mobile phones etc all need these special crystals. They make it possible for very complicated electrical circuits to be made that take up very little space.Artificial crystals are used to make computer ‘chips’ which have numerous everyday uses.

19. Re-cap session

 Activity Discussion Show PowerPoint Slide 37Revise

20. Finish off saying scientists do amazing things. (Slide 38)

 Activity Discussion Maybe leave them with some saturated salt solution and tell them that if the water evaporates veryslowly they will get bigger crystals. Explain that early computers took up a large room which was filled with racks of equipment These computers could do about the same as a ‘calculator’. Then asked whether iPods made by the same technology be any use – as they would take up several rooms!Scientists find out things and make new amazing things possible.Explain that scientists find answers to questions. They should keep asking questions.