Question

Derive the chemical formula of magnesium carbonate.

Answer 1

Molecular formula: molecular formula of a compound is the symbolic representation of the one molecule of a compound which shows the number of atom of each element that is present in it.

For example,${\mathrm{H}}_2\mathrm{O}$(water) molecule represents that water is made up of 2 atoms of hydrogen element and one atom of oxygen.

Steps for writing molecular formula:

• First write symbols of elements present in that compound. Elements with positive valency (metals) are placed on the right-hand side followed by the elements with the negative valency(non-metals).
• Now write the valency of each element below it.
• Now interchange the valency by the criss-cross method.
• The interchange valency is placed as a subscript of each element.
• If the compound is formed of polyatomic ions( ${\mathrm{SO}}_4^{2-}$)then the number of ions present in that compound is represented by enclosing the formula of the ion in a bracket and writing its number outside the bracket.

Molecular formula of Magnesium carbonate

• First, write symbols and valency of magnesium and carbonate ions.

$\underset{2}{\mathrm{Mg}}\underset{2}{{\mathrm{CO}}_3^{2-}}$

• Now interchange the valency by the criss-cross method.

$\underset{2\nearrow }{\mathrm{Mg}}\underset{\nwarrow 2}{{\mathrm{CO}}_3^{2-}}$

• Write interchange valency at the base of each ion.

$\underset{2}{\mathrm{Mg}}\underset{2}{{\mathrm{CO}}_3^{2-}}$

Thus the formula becomes${\mathrm{MgCO}}_3$.