Chemical Properties of Lithium and Sodium

Both lithium and sodium are extremely reactive metals. Sodium is more reactive than lithium.

Action of air

Both lithium and sodium remain unaffected by dry air but get readily tarnished in moist air forming a film of oxide. These oxides react with moisture of the air give the corresponding hydroxide and finally carbonate.

This is the reason that sodium and potassium are stored under kerosene.

With oxygen

Lithium tarnishes slowly in moist air while dry air has no effect. When heated in air or oxygen at about 200°C, it burns with a brilliant white light forming lithium monoxide.

When heated in air or oxygen, sodium burns with a golden yellow flame forming a mixture of oxide and peroxide.

Action of water

Both, lithium and sodium decompose cold water vigorously liberating hydrogen. Sodium reacts with water more vigorously than lithium.

The hydroxides of lithium and sodium are strong alkalies. They are highly soluble in water and their aqueous solutions contain hydroxyl ions:

Sodium hydroxide is a stronger base than lithium hydroxide.

Action with Non-metals

Both lithium and sodium combine directly with hydrogen, sulphur, halogens and other non-metals on heating.

With hydrogen

These hydrides are ionic hydrides.

With chlorine

These halides are ionic crystalline halides. Lithium halides are less ionic than sodium halides.

With sulphur

With phosphorous

With nitrogen

It may be noted that lithium reacts with N₂ to form lithium nitride but sodium does not form sodium nitride.

With ammonia

Sodium and potassium give the corresponding amide when heated in ammonia gas.

These amides act as reducing agents and reduce many oxides.

Reducing action

Lithium and Sodium act as strong reducing agents. So, they reduce some metallic chlorides and oxides into metals. This property is applied in the preparation of some metals. For example, beryllium, uranium etc., can be obtained by the reduction of the corresponding halides using sodium.

Action with acids

Sodium reacts vigorously with acids evolving hydrogen.

Action with mercury

With mercury, sodium form amalgams of varying composition e.g., NaHg, Na₂Hg, Na₃Hg etc.

Solubility in liquid ammonia

Sodium dissolves in liquid ammonia to give conducting blue-colored solution due to the presence of ammoniated electrons in solutions.

The blue color of the solution is due to ammoniated electrons, which absorb energy corresponding to red region of visible light, for their excitation to higher energy levels. The transmitted light thus imparts blue color to the solution.

The solution is made conducting in nature by both ammoniated cation and ammoniated electron.