Formulae
Chemistry: IB Diploma Higher Level, topic 3.6.7
Formulae
There are multiple kinds of formula that we use to represent molecules. They all give different information about a molecule.
Empirical formulae
- An empirical formula is the simplest whole number ratio of atoms in a molecule.
- E.g. CH3 is the empirical formula of ethane.
- E.g. CH is the empirical formula of benzene.
Molecular formulae
- The molecular formula of a compound gives the number of each type of atom in a molecule.
- E.g. C2H6 is the molecular formula of ethane.
Structural formulae
- The structural formula is a written one-line formula showing which groups are connected to which.
- E.g. CH3CH3 is the structural formula of ethane.
- E.g. CH3CH2CH2CH3 is the structural formula of butane.
Displayed formulae
- A displayed formula is a diagram which shows every bond in a molecule.
Skeletal formulae
- A skeletal formula is a simplified displayed formula.
- Hydrogen atoms are not shown and carbon atoms are at the corners of any lines.
- A skeletal formula shows the 'skeleton' of the molecule, hence the name.
Test yourself on Formulae
What type of formula is shown in this diagram?
What is the empirical formula of benzene?
Which of the following are accurate descriptions of formulae?