When a group 1 element takes part in a reaction, its atoms each lose one electron. This forms positively charged ions. The ions have a stable arrangement of electrons, with a complete outer shell.
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)
Write the word equation and balanced symbol equation for the reaction of potassium with water.
potassium + water → potassium hydroxide + hydrogen
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
The table shows observations when lithium, sodium and potassium are added to water. Notice that the reactivity of these metals increases going down the group. This pattern is seen with all reactions of group 1 elements. For example, the reaction of caesium with chlorine is more vigorous than the reaction of potassium with chlorine.
|Element||Observation when added to water|
|Lithium, Li||Fizzes steadily; slowly becomes smaller until it disappears|
|Sodium, Na||Fizzes rapidly; melts to form a ball; quickly becomes smaller until it disappears|
|Potassium, K||Burns violently with sparks and a lilac flame; quickly melts to form a ball; disappears 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 disappear almost instantly with an explosion.