Group 1 elements react with moist air. They are stored in oil to stop air and water vapour coming into contact with them. Moist air reacts with potassium to form potassium oxide. This creates a layer over the surface of the metal.
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)
potassium + water → potassium hydroxide + hydrogen
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
The table shows the main observations when lithium, sodium and potassium are added to water.
These observations may be used to find a pattern in the reactivity of the group 1 elements.
These observations show that the reactivity of these metals increases going down the group.
|Group 1 element||Observations|
|Lithium, Li||Fizzes steadily, and slowly becomes smaller until it has all reacted|
|Sodium, Na||Melts to form a ball, fizzes rapidly, and quickly becomes smaller until it disappears|
|Potassium, K||Quickly melts to form a ball, burns violently with sparks and a lilac flame, and reacts rapidly, often with a small explosion|
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 react almost instantly with an explosion.
Sodium + chlorine → sodium chloride
2Na(s) + Cl2(g) → 2NaCl(s)
The reactions get more vigorous going down the group.