Write the chemical formula of the following.

(a) Magnesium chloride

(b) Calcium oxide

(c) Copper nitrate

(d) Aluminium chloride

(e) Calcium carbonate

(a) Magnesium chloride

Step 1 — Write each symbol with its valency

$\text{Mg}^{2+} \phantom{\nearrow} \text{Cl}^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{2}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{Cl}} \Rightarrow \underset{\phantom{1}{1}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{Cl}} \\[0.5em]$

Step 3 — Write the interchanged number, ignore equal numbers & hence the formula

Therefore, we get

Formula of Magnesium chloride : $\bold{MgCl_2}$

(b) Calcium oxide

Step 1 — Write each symbol with its valency

$\text{Ca}^{2+} \phantom{\nearrow} \text{O}^{2-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{O}} \Rightarrow \underset{\phantom{1}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{O}} \\[0.5em]$

Step 3 — Write the interchanged number, ignore equal numbers & hence the formula

Therefore, we get

Formula of Calcium oxide : $\bold{CaO}$

(c) Copper nitrate

Step 1 — Write each symbol with its valency

$\text{Cu}^{2+} \phantom{\nearrow} \text{NO}_3^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{2}}{\text{Cu}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{NO}$3} \Rightarrow \underset{\phantom{1}{1}}{\text{Cu}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{NO}3} \\[0.5em]

Step 3 — Write the interchanged number, ignore equal numbers & hence the formula

Therefore, we get

Formula of copper nitrate : $\bold{Cu(NO$3)2}

(d) Aluminium chloride

Step 1 — Write each symbol with its valency

$\text{Al}^{3+} \phantom{\nearrow} \text{Cl}^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{3}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{Cl}} \Rightarrow \underset{\phantom{1}{1}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \underset{3}{\text{Cl}} \\[0.5em]$

Step 3 — Write the interchanged number, ignore equal numbers & hence the formula

Therefore, we get

Formula of Aluminium chloride : $\bold{AlCl_3}$

(e) Calcium carbonate –

Step 1 — Write each symbol with its valency

$\text{Ca}^{2+} \phantom{\nearrow} \text{CO}_3^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{CO}$3} \Rightarrow \underset{\phantom{1}{1}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{CO}3} \\[0.5em]

Step 3 — Write the interchanged number, ignore equal numbers & hence the formula

Therefore, we get

Formula of copper nitrate : $\bold{Ca(CO$3)2}