Structural Formula
A formula that shows how atoms are arranged and bonded within a molecule — not just how many atoms are present. Structural formulae are most commonly used in organic chemistry.
Example: Ethanol can be written as C₂H₅OH as a structural formula, showing that the OH group is separate from the rest of the molecule.
Ionic Formula
The formula of an ionic compound written to show the charges on each ion. Used to understand how ions combine to form neutral compounds.
Example: The ionic formula of sodium chloride is Na⁺Cl⁻. Calcium chloride is Ca²⁺(Cl⁻)₂, showing that two chloride ions balance one calcium ion.