Lithium is the first element in group 1 of the Periodic Table. The observations for the reaction of lithium and water are:

  1. fizzing (hydrogen gas is released)
  2. lithium floats and moves around on the water
  3. lithium disappears

Sodium is the second alkali metal in the group. The reaction of sodium and water is more vigorous than lithium’s:

  1. fizzing (hydrogen gas is released)
  2. sodium floats and moves around on the water
  3. sodium melts into a silver-coloured ball
  4. sodium disappears

Potassium is the second alkali metal in the group. The reaction of potassium and water is more vigorous than sodium’s:

  1. fizzing (hydrogen gas is released)
  2. potassium floats and moves around on the water
  3. catches fire with a LILAC flame
  4. potassium disappears

When the group 1 metals react with air they oxidise, showing a similar trend in reactivity as we go down the group of the Periodic Table.

Therefore, as we go down group 1 (increasing atomic number), the elements become more reactive: Li<Na<K<Rb<Cs<Fr