Structural Formula

Complete structural formulas show all the atoms in a molecule, the types of bonds connecting them, and how they are connected with each other. For a simple molecule like water, H₂O, the molecular formula, becomes H-O-H, the structural formula. This structural formula shows that in a water molecule, the oxygen atom is the central atom, and it is connected by single covalent bonds to the hydrogen atoms. Carbon dioxide, CO₂, can be represented structurally as O=C=O. This structural formula tells you that in this case the carbon atom is the central one, and the oxygen atoms are joined by double covalent bonds to the carbon atom.

For small molecules like these, the amount of new information in a structural formula is not great, but structures become more important when we study larger molecules. Let's look at the molecular formula C₂H 6O. With some knowledge of valences for the three kinds of atoms involved, we can arrange these atoms in a complete structural formula as shown below.

This is the formula of ethanol, which is well-known for its intoxicant and antiseptic properties, and is also being used in reformulated gasoline. It is a liquid with a boiling point of 172°F (78°C). However, we can also produce another structural formula that satisfies all the bonding requirements for the atoms involved but shows a completely different molecule.

This molecule is methyl ether. It is a gas at room temperature and has very different chemical properties from ethanol.