With reference to valencies, describe and explain the differences in reaction as you go down group 1 of the periodic table for the reaction: metal + water -> Metal hydroxide + hydrogen.

As you descend the group, the reactions become more vigorous, more exothermic and have a higher rate of reaction. Lithium will just gently fizz and produce a gas, sodium will melt into a ball shape and fizz more vigorously, and potassium sets alight with a lilac flame.

The explanation for this is because as you go down the group, the number of electron shells is increased, and the single electron on the outer shell is further away. The electron configurations are : Lithium [2,1] Sodium [2,8,1] potassium [2,8,8,1] and so on. The effect that this has is that the forces of attraction between the nucleus (with an overall positive charge) and the outermost electron (with a negative charge) decreases as you descend the group, which means that as you descend the group, the activation energy of the reaction decreases. As the activation energy decreases, the reactivity of the substance increases, so therefore the reactivity of the metals increase steadily. As you descend the group it is easier in a sense for the hydroxide ion (from the water) to take that outer electron, hence the reaction occurs more quickly and more vigorously.