A structural formula shows the actual number of atoms of each element present along with the structural composition of the molecule. There are several different systems for representing a structural formula. The Lewis structure or electron dot structure represents the valence electrons as dots. The nucleus and the core electrons are represented by the element symbol.

Structural formula, whether expanded or condensed do not show the geometry (shape) of the molecule. A structural formula also indicates the type of bonds that are present within a molecule, that is the presence of single, double and triple covalent bonds.

Some of the solved problems based on structural formula is given below:

Question 1: Give the molecular formula and draw the structural formula and condensed structural formula for the alkane with nine carbon atoms.
Solution:
The molecule contains nine carbon atoms, and therefore 2(9) + 2 = 20 hydrogen atoms, its molecular formula is as follows. 

Nonane

Its condensed structural formula is CH3CH2CH2CH2CH2CH2CH2CH2CH3 (or) CH3(CH2)7CH3.

Question 2: Draw the full structural formula and condensed structural formula of butane.
Solution:
List each carbon atom in the molecule ad then add the hydrogen atoms that are bonded to each carbon. 

Butane
Its condensed structural formula is CH3CH2CH2CH3.