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WJEC GCSE Additional Science Teacher’s Notes PRACTICAL Making molecular models (page 106) A unit cell is the smallest repeating unit in the structure of a giant structure. sodium chloride unit cell diamond unit cell graphite unit cell _ Carbon nanotubes (pages 106–107)______________ Questions 24. What are carbon nanotubes Carbon nanotubes are another allotrope of carbon produced when graphite layers form and then roll up into tubes rather than being deposited in layers. 25. Why are materials made from carbon nanotubes a good choice for components on a bike Carbon nanotubes are incredibly strong, but very lightweight. This makes them ideal for use on high performance bicycle components. 26. Why do carbon nanotubes conduct electricity How could they be made into electrical connections inside electronic devices Carbon nanotubes are good conductors of electricity due to the free electrons that can move up and down the tubes. The tubes could be manufactured to behave like electrical wire connections between electronic components on printed circuit boards – with very high conductivities yet 10 000 times thinner than a human hair! Discussion point Carbon nanotubes are definitely a material for the future – can you think of any good applications for a very lightweight, incredibly strong, electrically conducting material Lots of military applications, portable computing, mobile phones, aerospace engineering, etc. _Smart materials (pages 108–109)________________ Questions 27. What is a ‘smart material’ Smart materials have properties which change reversibly with a change in their surroundings. 28. Explain the difference between: a a thermochromic pigment and a photochromic pigment A thermochromic pigment changes colour with changing temperature, whereas a photochromic pigment changes colour with changing light intensity. 34
WJEC GCSE Additional Science Teacher’s Notes b a shape-memory polymer and a shape-memory alloy Shape memory materials return to their original shape once deformed when heated. Shapememory polymers are made of ‘plastic’ materials whereas shape-memory alloys are metals. 29. How can hydrogels be made to absorb more or less water By changing their temperature or pH. 30. Explain why smart materials are used to manufacture: a photochromic flexi glasses Photochromic flexi glasses – can be bent out of shape yet returned to their original shape and get darker as the intensity of the sunlight increases. b sport gum-shields Sport gum-shields – can be heated to allow them to be fitted snuggly to the teeth, and then cooled to retain the shape. If the gum-shield needs to be re-fitted it can simply be heated up, returned to its original shape and then re-fitted to the teeth. c battery power indicators Battery power indicators – a thermochromic pigment can be mixed with a conducting substrate and ‘painted’ onto the side of a battery. When fingers complete the circuit a small current flows through the conducting substrate which heats up the thermochromic paint causing it to change colour – more current, more heat, different colours. d novelty T-shirts T-shirts that change colour due to changes in body or surrounding temperature or changes in the ambient light intensity. 35
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