From Atoms to Materials

proton electron Fig. 13.11 A simplified diagram of a hydrogen atom (not drawn to scale). It contains 1 proton and 1 electron. 20 protons in nucleus 18 electrons calcium atom calcium ion loses 2 electrons 20 protons in nucleus 20 electrons Language tip cation noun (pronunciation: cat - ion ) ion 離子 positive ion 正離子 cation 陽離子 Extension Ions We learnt that an atom is electrically neutral, as it contains the same number of protons (positively charged) and electrons (negatively charged). E What will happen if the protons and the electrons are not equal in number? When this happens, there must be a net positive charge or a net negative charge, and the atom becomes an ion . Positive ions When an atom loses electron(s), there are fewer electrons in the atom than protons. The ion formed will carry a net positive charge . It is called a positive ion or a cation . For example, a calcium atom has 20 protons and 20 electrons. Under certain conditions, it can lose two electrons to form a calcium ion. A calcium ion is a positive ion (a cation); it carries two positive charges. Fig. 13.12 A calcium atom (left) loses two electrons to form a calcium ion (right). 25 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