Chapter 9 develops a systematic understanding of the periodic trends in physical and chemical properties of the elements, using Period 3 as the primary case study. The chapter demonstrates how atomic structure and bonding type together determine the observable behaviour of elements and their compounds.

The chapter opens with the physical properties of the Period 3 elements, examining periodic variations in atomic radius, ionic radius, melting point and electrical conductivity. These trends are rationalised in terms of the underlying structure and bonding of each element. The chemical properties of Period 3 are then treated in depth, covering the reactions of the elements with oxygen, chlorine and water, the acid-base behaviour of the resulting oxides and hydroxides, and the reactions of the chlorides with water. Throughout, the variations in oxidation state, bond type and reactivity are explained in terms of electronegativity and valence electron configuration. The chapter closes by extending these principles beyond Period 3, equipping candidates to predict the properties of unfamiliar elements from their position in the periodic table.