4. Derive the molecular formulae of the following compounds stepwise and give their atomicity.

v. sodium nitrate

Derive the molecular formulae of sodium nitrate stepwise and give their atomicity:

1. Write the symbols of the elements or the ions forming the compound.
$\mathrm{Na}{\mathrm{NO}}_3$
2. Write the valency of each as a superscript to the top right. Ignore the + and - signs of ions.
${\mathrm{Na}}^1{{\mathrm{NO}}_3}^1$
3. Interchange the valencies and bring them down diagonally.

4. Write the interchanged valencies as subscripts. Place polyatomic ions in parentheses if the subscript is greater than 1.
${\left(\mathrm{Na}\right)}_1{\left({\mathrm{NO}}_3\right)}_1$

5. Ignore the number 1. Reduce the numbers to the lowest ratio. Write the chemical formula.
${\mathrm{NaNO}}_3$

• Atomicity: Atomicity is the total number of atoms in a molecule. Molecules may be monoatomic, diatomic, triatomic, or polyatomic depending on the number of atoms. Thus, the atomicity of ${\mathrm{NaNO}}_3$ is 5.