Structural Formula

A structural formula is a chemical formula that gives you a more complete picture of a compound than its molecular formula can. While a molecular formula, such as H₂O, shows the types of atoms in a substance and the number of each kind of atom, a structural formula also gives information about how the atoms are connected together. Some complex types of structural formulas can even give you a picture of how the atoms of the molecule are arranged in space. Structural formulas are most often used to represent molecular rather than ionic compounds.

There are several different ways to represent compounds in structural formulas, depending on how much detail needs to be shown about the molecule under consideration. Illustration by Hans & Cassidy. Courtesy of Gale Group.
We will look at complete structural formulas, condensed formulas, line formulas, and three-dimensional formulas.

After you become familiar with the rules for writing complete structural formulas, you find yourself taking shortcuts and using condensed structural formulas. You still need to show the complete molecule, but the inactive parts can be more sketchily shown. Thus the two formulas above look like this when written in condensed form: