From Atoms to Materials

Gold and silver 1. Gold and silver can be easily extracted from their ores using physical methods. Therefore, they were among the earliest metals discovered. 2. Gold and silver are not widely used because of their softness and low abundance. Iron 1. Iron is moderately abundant in the Earth’s crust. 2. It is quite easy to extract iron from its ores. Therefore, iron was discovered and used much earlier than aluminium. Aluminium 1. Aluminium is the most abundant metal in the Earth’s crust. 2. However, aluminium was used very late in human history. Extraction of aluminium needs electricity, which became widely available only about 200 years ago. Bronze is a mixture of copper and tin. We shall learn more about bronze later in this section. The most abundant metal in the Earth’s crust is aluminium, followed by iron and calcium. For more information about the abundance of metals, refer to p. 24. Let’s Think Discoveries of copper and iron Iron is more abundant than copper in the Earth’s crust. Why was iron discovered and used later than copper? From the timeline, we see that copper, bronze and iron were the major metallic materials used by humans one after another in history. Why were they used in that order? In fact, the order that metals were discovered and used by humans depends on two factors: 1. abundance of the metals in the Earth’s crust 2. ease of extraction of the metals from their ores Let’s study these two factors in the cases below. 73 13 From Atoms to Materials © 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