A demonstration of the relative speeds of surface corrosion of alkali metals and their reaction with water. The alkali metals are all soft metals that can be cut with a knife. They all react quickly with oxygen in air, and with water. The rate of reaction increases as you go down the group in the periodic table.
Ask students to explain the reactivity of alkali metals in terms of their atomic structure. They should also explain why the metals become more reactive as you move down through the group. This could then be related to the construction of the electrochemical series.