Types of Formulas
Chemistry: IB Diploma Higher Level, topic 3.6.5
Types of Formulas
There are multiple ways of representing an organic molecule by using different types of chemical formulas.
Molecular and empirical
- Molecular formula represents the number of each atom within a molecule.
- Empirical formula represents the simplest whole-number ratio of atoms in a molecule.
- The table above shows some examples to demonstrate the relationship between molecular and empirical formulas.
Structural
- Structural formulas show the location of bonds within a molecule.
- This full structural formula shows a 2-D representation of the molecule identifying all bonds and their order.
- The full structural formula does not necessarily show the true geometry of the molecule.
Condensed
- Condensed structural formulas allow chemists to condense the structure onto a single line.
- Bonds are removed from the structure when possible and the bond order can be established by considering the number of substituents around each atom.
- Repeating horizontal units can be summarised in brackets with a subscript.
Skeletal
- The skeletal structure omits carbon and hydrogen atoms from the structure and only shows the carbon skeleton with functional groups.
3-D representations (stereochemical)
- Stereochemical formulas try to demonstrate the geometry around carbon atoms in an organic molecule.
- Stereochemical formulas order the atoms and groups into 3-D spaces relative to each other around a central carbon.
- Typically, a solid wedge represents a bond pointing forwards, and bonds pointing backward in space are notated with a broken wedge.
- Bonds in the plane of the paper are notated by single lines.
3-D representations
Test yourself on Types of Formulas
Which of these statements is correct?