4.31 Physical Properties
All the Group 1 elements are silvery-coloured metals.
They are soft, and can be easily cut with a knife to expose a shiny surface.
They have low melting and boiling temperatures.
They have low densities - Li, Na and K are less dense than water.
4.32 Reactivity
These elements are highly reactive metals.
All elements in Group 1 have one valence electron each.
The reactivity increases on descending the Group from lithium to cesium.
4.33 Reaction with Oxygen
The alkali metals react vigorously with oxygen and form ionic solid oxides of composition M2O.
4M + O2 → 2M2O
This equation applies to any of these metals and water - simply replace M with any element of Group 1.
Lithium and potassium react with oxygen almost the same manner as sodium. The difference is that lithium is less reactive while potassium is more reactive than sodium.
4Li + O2 → 2Li2O
4K + O2 → 2K2O
Reaction of sodium with oxygen
4.33 Reaction with Water
All of these metals react vigorously or even explosively with cold water.
In each case, a solution of the metal hydroxide is produced together with hydrogen gas.
2M + 2H2O → 2MOH + H2
This equation applies to any of these metals and water - simply replace M with any element of Group 1.
Let us look at a reaction between sodium and water.
Lithium and potassium react with water almost the same manner as sodium. The difference is that lithium is less reactive while potassium is more reactive than sodium.
2Li + 2H2O → 2LiOH + H2
2K + 2H2O → 2KOH + H2
Reaction of lithium with water
Reaction of sodium with water
Reaction of potassium with water
