Alkali metals react with water and emit hydrogen gas and form relevant metal hydroxides. These metal hydroxides dissolve very well in water and form strong bases
M = Li or Na or K or Rb or Cs
Reactivity of metals increase when going down the group. That means sodium reacts so fast with water than lithium does. Like that, potassium reacts faster than sodium.
Also remember that, reaction of water with sodium or potassium is very dangerous because fires can be occurred. Therefore you should be careful when experiments are conducted.
Lithium's density is lower than water. Therefore lithium floats on the surface of water, gently fizzing and giving off hydrogen gas. Lithium gradually reacts with water and disappears, forming a colorless solution of lithium hydroxide (LiOH). The reaction generates heat too slowly.
As lithium, sodium also floats on the surface, but enough heat is generated to melt the sodium metal (melting point of sodium is lower than lithium and the reaction produces heat faster) and it melts almost at once to form a small silvery ball that dashes around the surface. A white trail of sodium hydroxide is seen in the water under the sodium, but this soon dissolves to give a colorless solution of sodium hydroxide (NaOH) which is common chemical in laboratories and industries.
Fires can be occurred sometimes during the reaction.
Potassium behaves similar to sodium except that the reaction is faster than sodium and enough heat is given in a very short time. As the product potassium hydroxide (KOH) is given. potassium hydroxide also has so many uses like sodium hydroxide.
Rubidium is denser than water and so sinks. Rubidium reacts violently with water. Due to release of heat immediately, everything can be thrown away from container by injuring if people are gathered close to the experiment. Rubidium hydroxide (RbOH) solution and hydrogen gas are formed as results.
Caesium and water reaction give explosions. Caesium hydroxide (CsOH) and hydrogen gas are formed
These reactions of group 1 metals and water are exothermic reactions. Heat is released when reactions are occurred. Following table you can see the enthalpy change of alkali metals and water reactions.
This question is not limited to alkali metals and water reaction. When going down the group, metallic radius of alkali metals increases. When metallic radius increases, it reduces the attraction between nucleus and electron of last shell. Because, attraction is weak, eliminatting that last shell electron is easy. Therefore, when going down the group, alkali metals (group 1 metals) reacts fast wwith water to give products.
Questions asked by students
Alkali metals like sodium, potassium release large heat in a short time during the reaction (Reaction occurs so fast). Due to that heat temperature rises and it will cause to begin fires.
You know, alkaline earth metals (group 2 elements) are not reactive like alkali metals. Therfore, their reactivity with water is less compared to alkali metals. From alkaline earth metals, calcium, strontium and barium reacts with water. Magnesium and beryllium do not react with water. But, all alkali metals react with water to form strong base solution.
A strong basic solution and hydrogen gas is formed. Basic characteristic of the solution increases when going down the group. That means, NaOH is more basic than LiOH. All group 1 metals's hydroxides are strong bases. When group 1 elements react with water, due to formation of strong base, pH value will be high.
You can see alkali metals react with water very fast. When going down the group, reaction rate increases and explosions can be happened due to release of large heat in a short time.
Lithium, sodium, potassium, rubidium, caesium and francium belongs to alkali metals. We see, reaction rate of group 1 metals with water increases when going down the group. Therefore, all group 1 metals should react with water. But, due to rareness of francium, experiments may be not done to test its reactivity with water.
Group IA metals react with water to produce metal hydroxides and hydrogen gas. Group IA metal is oxidized.