From Atoms to Materials

Snapshot Explaining alloys’ properties Alloys have properties different from their corresponding pure metals. This can be explained in terms of atoms. Snapshot Carats (or K) % gold by mass 24 K 100% 18 K 75% 12 K 50% Carat gold of different colours, e.g. pinkish, greenish and yellowish. They are often used in making jewellery. Carat gold ‘Carat’ is a measure of the purity of gold by mass: Depending on their compositions, gold alloys may have different colours. Pure metal Atoms are packed regularly. Layers of metal atoms can slide over each other more easily. Alloy Atoms of different sizes distort the regular packing of atoms. Layers of metal atoms slide less easily. This causes changes in physical properties. layers slide over each other push layer slips easily no change – the different atom jams up the structure push push layers cannot easily slide over each other push push layer slips easily no change – the different atom jams up the structure push 78 © United Prime Educational Publishing (HK) Limited 2024 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publisher. Sample