What is the difference between expanded and condensed structural formulas?
Expanded structural formula shows all of the bonds in the compound.
Condensed structural formula omits most or all of the bonds.
Expanded structural formula shows all of the bonds connecting all of the atoms in the compound.
Condensed structural formula shows all atoms, but omits some or all of the vertical and horizontal bonds. It makes it easier to write the formula in a line.
Here are the different ways condensed structural formula can be represented:
Here's a video that shows how to draw structural formula for organic compounds - Expanded, Condensed and Skeletal form: