Group 1 metals, such as potassium, sodium and lithium, react with water to produce a metal hydroxide and hydrogen. For example:

          lithium   +   water   →   lithium hydroxide   +   hydrogen

          2Li (s)   +   2H₂O (l)   →   2LiOH (aq)   +   H₂ (g)

The observations for this reaction of lithium and water are:

  1. Fizzing
  2. Lithium floats and moves around on the water
  3. Lithium disappears

The reactions of sodium or potassium and water are somewhat similar, giving those observations and producing a metal hydroxide and water.

This similarity in reactions provides evidence that the 3 metals are in the same family of elements (group of the Periodic Table).