From Atoms to Materials

hydrogen atom helium atom hydrogen atom helium atom Fig. 13.8 Atoms of different elements have different numbers of protons. Note that: •  The atoms of the same element have the same number of protons. Using the number of protons, we can arrange the elements in order, as in Table 13.2. •  In every atom, the number of protons is equal to the number of electrons. As each proton has a positive electric charge (+1), and each electron has a negative electric charge (−1), the atom has no overall charge. We say the atom is electrically neutral*. 1 proton, 0 neutrons 2 neutrons, 2 protons 1 electron 2 electrons electrically neutral 電中性 chemical symbol 化學符號 The atoms of different elements have different sizes, as they have different numbers of subatomic particles. • Atoms of the same element have the same number of protons. • An atom has the same number of protons (+1 charge) and electrons (−1 charge). Therefore, an atom is electrically neutral. How to represent elements and atoms? Representing elements Scientists around the world use a set of chemical symbols* to represent elements. The chemical symbols of some elements are shown in Table 13.3 on the next page. C People around the world can understand these signs, regardless of what languages they speak. 16 © 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