From Atoms to Materials

2. When we examine the physical properties of substances, no new substance is formed . 3. When we examine the chemical properties of substances, new substances are formed . 13.2 Atoms and elements A. What is inside an atom? (p. 10) 1. An atom consists of protons, electrons and neutrons. 2. The centre of an atom is a small, dense region called the nucleus. Protons and neutrons are packed tightly together in the nucleus. 3. Electrons occupy space outside the nucleus. B. How are atoms and elements related? (p. 14) 4. Atoms of the same element have the same number of protons. 5. An atom has the same number of protons (+1 charge) and electrons (−1 charge). Therefore, an atom is electrically neutral. C. How to represent elements and atoms? (p. 16) 6. Each element is represented by a chemical symbol. 7. Atomic number is the number of protons in an atom. 8. Mass number is the sum of the numbers of protons and neutrons in an atom. D. How to classify elements? (p. 21) 9. Elements can be classified into metals, non-metals and semi-metals, according to their physical properties. 10. Semi-metals show properties in between those of metals and non- metals. E. Ions (p. 25) 11. When an atom loses electron(s), it carries a net positive charge and forms a positive ion (a cation). 12. When an atom gains electron(s), it carries a net negative charge and forms a negative ion (an anion). atom (electrically neutral) positive ion negative ion loses electron(s) gains electron(s) Chapter Review 13 From Atoms to Materials 107 © 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