After you have studied this lesson you should be able to:

• give the definition for molecular formulas and describe the information they convey
• tell what information a structural formula provides
• tell what is meant by a Lewis structure
• describe what is meant by a lone pair

A molecular formula gives the types and the count of atoms for each element in a compound. An example of a molecular formula is ethane, C₂H₆. Here the formula indicates carbon and hydrogen are combined in ethane. The subscripts tell us that there are 2 carbon atoms and 6 hydrogen atoms in a formula unit.

The structural formula shows the atoms in a formula unit and the bonds between atoms as lines. Single bonds are one line, Double bonds are two lines. Triple bonds are three lines. The Lewis dot structure shows the number of valence electrons and types of bonds in the molecule.

Lewis dot structure

Ball and stick model