Alkali metals are more
reactive in their reactions with water when going down the group. Group 1
elements react with water to form an alkaline metal hydroxide solution and
hydrogen gas, H2.
- Lithium melts and moves slowly at random on the surface of water with plenty of fizz. A colorless solution that turns red litmus paper blue is formed.
2Li (s) + 2H2O
(l) → 2LiOH (aq) + H2 (g)
- Sodium melts and moves rapidly at random on the surface of water with a hissing sound. A colorless solution that turns red litmus paper blue is formed.
2Na (s) + 2H2O
(l) → 2LiOH (aq) + H2 (g)
- Potassium melts moves very fast at random on the surface of water and ignites with a lilac flame, with ‘pop’ and hissing sounds. A colorless solution that turns red litmus paper blue is formed.
2K (s) + 2H2O
(l) → 2KOH (aq) + H2 (g)
The arrangement of the Group
1 elements in ascending order of their reactivity is lithium, sodium and
potassium.