How do structural formulae differ from molecular formulae?

Structural formulae show the arrangement of atoms in a molecule, while molecular formulae only show the types and numbers of atoms.

Structural formulae and molecular formulae are both ways of representing the composition of a molecule. However, they provide different levels of information. A molecular formula simply tells you which atoms are present in a molecule and in what quantities. For example, the molecular formula of ethanol is C2H6O, which tells us that an ethanol molecule contains two carbon atoms, six hydrogen atoms, and one oxygen atom.

On the other hand, a structural formula provides more detailed information. It shows how the atoms in a molecule are connected to each other. For instance, the structural formula of ethanol shows that one of the carbon atoms is connected to the oxygen atom, which is in turn connected to a hydrogen atom, while the other carbon atom is connected to three hydrogen atoms. This level of detail can be very important in chemistry, as the structure of a molecule can greatly influence its properties and behaviour.

In addition, structural formulae can also show the three-dimensional shape of a molecule, which can be crucial for understanding how a molecule interacts with other molecules. For example, the structural formula of a molecule like water (H2O) shows that the two hydrogen atoms are not directly opposite each other, but are instead arranged in a V shape. This shape is a key factor in many of water's unique properties, such as its ability to form hydrogen bonds.

In summary, while both molecular and structural formulae provide valuable information about a molecule, structural formulae offer a more detailed and comprehensive view of a molecule's composition and structure.