Let’s look at how group 1 metals react with water, oxygen and chlorine.
Group 1 metals react rapidly with water to form a metal hydroxide and hydrogen gas. For example, sodium will react with water to form sodium hydroxide and hydrogen gas:
Sodium + Water → Sodium hydroxide + Hydrogen
When this reaction occurs, you will observe effervescence (bubbling) as hydrogen gas is released. Sodium is an alkali, and when it reacts with water, it creates a solution with a pH greater than 7. This can be confirmed by adding a universal indicator and observing a blue or purple colour.
Alkali metals get more reactive as you go down the group, and the reactions will release more energy. So, water will react more rapidly with lithium than sodium.
Group 1 metals react with oxygen in the air to form metal oxides. This reaction occurs naturally when the metal is cut, and a layer of metal oxide forms on its surface. For example, the reaction between lithium and oxygen produces lithium oxide:
Lithium + Oxygen → Lithium oxide
4Li(s) + O2(g) → 2Li2O(s)
Group 1 metals react more rapidly with oxygen as you go down the group.
Group 1 metals react rapidly when heated in chlorine gas to form metal chloride salts. For example, sodium reacts with chlorine to form sodium chloride (NaCl), commonly known as table salt:
Sodium + Chlorine → Sodium chloride
2Na(s) + Cl2(g) → 2NaCl(s)
Group 1 metals react more rapidly with chlorine as you go down the group.