This clip explains the reasons for the increased reactivity of elements down group 1 in the periodic table in terms of electrons. Footage of the elements reacting with water is seen. The same principle is applied to group 7. A summary is given at the end.
Ask students to investigate changes to reactivity related to moving down a group or across a period and explain in their own words why this changes. Link this to observations of reaction of metals with oxygen, water and dilute acid, and the creation of reactivity series.