Question

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

1. Bonding
2. Action of air
3. Action of water
4. Action of acid

Answer 1

(a) Alkali metals:

(i) Bonding- The alkali metal salts are ionic in nature. For example, $\mathrm{NaCl}(\mathrm{sodium}\mathrm{chloride}),\mathrm{KCl}(\mathrm{potassium}\mathrm{chloride})$.

(ii) Action of air- They react rapidly with water and oxygen in the air and form metal oxide.

$$\begin{gathered} 4\mathrm{Li}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{Li}}_2\mathrm{O}\left(\mathrm{s}\right) \\ \mathrm{alkali}\mathrm{metal}\mathrm{oxygen}\mathrm{metal}\mathrm{oxide} \end{gathered}$$

(iii) Action of water- Alkali metals react with water to produce metal hydroxide and hydrogen gas.

$$\begin{gathered} 2\mathrm{M}\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\mathit{}\mathit{}\mathit{}\to 2\mathrm{MOH}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{alkali}\mathrm{metal}\mathrm{water}\mathrm{metal}\mathrm{hydroxide}\mathrm{hydrogen} \end{gathered}$$

(iv) Action of the acid- On reaction with dilute $\mathrm{HCl}$ and dilute. ${\mathrm{H}}_2{\mathrm{SO}}_4$, they produce metal salt and hydrogen gas.

$$\begin{gathered} 2\mathrm{M}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{l}\right)\to 2\mathrm{MCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{alkali}\mathrm{metal}\mathrm{hydrochloric}\mathrm{acid}\mathrm{metal}\mathrm{chloride}\mathrm{hydrogen} \end{gathered}$$

(b) Alkaline earth metals:

(I) Bonding- The alkaline earth metal salts except beryllium are ionic compounds. For example, ${\mathrm{MgBr}}_2(\mathrm{magnesium}\mathrm{bromide})$, ${\mathrm{CaCl}}_2(\mathrm{calcium}\mathrm{chloride})$

(ii) Action of air- They are less reactive than alkali metals towards the air.

$2\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{MgO}\left(\mathrm{s}\right)$

(iii) Action of water- They also react with water to produce metal hydroxide and hydrogen gas.

$$\begin{gathered} \mathrm{M}\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{M}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{alkaline}\mathrm{metal}\mathrm{water}\mathrm{metal}\mathrm{hydroxide}\mathrm{hydrogen} \end{gathered}$$

(iv) Action of acid- They react with dilute. $\mathrm{HCl}$ or dilute .${\mathrm{H}}_2{\mathrm{SO}}_4$ to give metal salt and hydrogen gas.

$$\begin{gathered} \mathrm{M}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{l}\right)\to {\mathrm{MCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{alkaline}\mathrm{melal}\mathrm{hydrochloric}\mathrm{acid}\mathrm{metal}\mathrm{chloride}\mathrm{hydrogen} \end{gathered}$$