Question

Give the general characteristics of alkali metals and alkaline earth metals with reference to (a) action of water and (b) reactivity.

Answer 1

(a) Alkali metals

• The group $IA$ metals are known as alkali metals. They are called so as they form hydroxide on reaction with $H_{2}O$.
• This series include $Li,Na,K,Rb,Cs,$ and $Fr$.
• They react with $H_{2}O$ and form metal hydroxides. The reaction can be generalized as:

$2M+2H_{2}O\to 2MOH+H_2 (alkali metals)$

• They are very reactive as they have one electron in their valence shell, and they readily loose it, this is the reason why they don’t occur in free state.
• $Na$ is very reactive and it is stored in kerosene.

(b) Alkaline earth metals:

• The group $IIA$ metals are known as alkaline earth metals. They include $Be,Mg,Ca,Sr,Ba,$ and $Ra$.
• They react with water to form hydroxides and give hydrogen gas as products. The reaction can be generalized as:

$M+2H_{2}O\to M{\left(OH\right)}_2+H_2 (alkaline earth metals)$

• They are less reactive than alkali metals as they have only $2$ electrons in the valence shell. They occur in combined form. The size increases down the group, so the reactivity also increases as it can lose the $2$ electrons more easily.