Comparing materials by their properties
Chemistry · Key Stage 2 · The School
A property is something you can test for
A property is something you can test for. How hard is it? Can you see through it? Does it carry heat? Does it carry electricity? Does it dissolve? Does a magnet pull it? Each one is a question. You get the answer from an experiment, not from an opinion. That is what makes it a property. Words like nice or strong-looking are only descriptions.
An old school science test sets out a spoon test. A blob of margarine sticks a bead to each handle. Each spoon stands in hot water with its handle out. An adult must pour the hot water. Only the material should change, so a fair version keeps the spoon size, the bead, the blob and the water the same. Change two things and you cannot say which change caused the result. The test gives these results. On the metal spoon, the margarine melted and the bead slipped off at 4 minutes 20 seconds. On the wooden spoon, the bead had not moved after 15 minutes. Now work out the gap. Take 4 minutes 20 seconds away from 15 minutes. That leaves 10 minutes 40 seconds. So the wooden spoon took at least 10 minutes 40 seconds longer. Heat passed along the metal spoon much more quickly. Metal carries heat well and wood does not, so wood is the better choice for stirring hot food.
Properties explain choices
Saucepans are metal with plastic handles. Metal carries heat well and plastic does not. Windows are glass because it is see-through and waterproof. Wires are copper inside plastic. Copper carries electricity and plastic does not. In every case the property came first. The choice followed from it.
Thermal and electrical conductors are usually the same materials
Metals usually carry both heat and electricity. That is not a coincidence. In both cases the same loosely-held electrons are free to carry energy through the metal. Non-metals mostly do neither. Graphite is the famous exception. It carries electricity when most non-metals do not. That is why it is used for pencil leads and for electrodes.