Group 1 - chemical reactions with water

Atoms of group 1 elements all have one electron in their outer shell. This means that the alkali metals all have similar chemical properties.

When a group 1 element takes part in a reaction, its atoms each lose one electron. This forms positively charged ions. The ions have a stable arrangement of electrons, with a complete outer shell.

Reactions with water

The alkali metals react with water to produce a metal hydroxide and hydrogen. For example, sodium reacts with water:

sodium + water → sodium hydroxide + hydrogen

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Sodium hydroxide is an alkali. It is a base that dissolves in water to form an alkaline solution. This solution:

Question

Write the word equation and balanced symbol equation for the reaction of potassium with water.

potassium + water → potassium hydroxide + hydrogen

2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

Reactions compared

The reaction of potassium with water gives a lilac flame
The reaction of potassium with water gives a lilac flame

The table shows observations when lithium, sodium and potassium are added to water. Notice that the reactivity of these metals increases going down the group. This pattern is seen with all reactions of group 1 elements. For example, the reaction of caesium with chlorine is more vigorous than the reaction of potassium with chlorine.

ElementObservation when added to water
Lithium, LiFizzes steadily; slowly becomes smaller until it disappears
Sodium, NaFizzes rapidly; melts to form a ball; quickly becomes smaller until it disappears
Potassium, KBurns violently with sparks and a lilac flame; quickly melts to form a ball; disappears rapidly, often with a small explosion
Question

Rubidium is placed below potassium in group 1. Predict what is seen when rubidium is added to water.

Rubidium should melt very quickly. It should burn very violently, and disappear almost instantly with an explosion.