Formula of a Molecule
Chemistry: Cambridge International GCSE Supplement, topic 11.1.1
Formula of a Molecule
A molecular formula shows the number and type of atoms in a molecule, while a displayed formula also shows how the atoms are bonded together.
Molecular formula
- A molecular formula shows the number and type of atoms in a molecule.
- For example:
- Water → H2O (2 hydrogen atoms, 1 oxygen atom)
- Carbon dioxide → CO2 (1 carbon atom, 2 oxygen atoms)
Displayed formula
- A displayed formula shows all the atoms and all the covalent bonds in a molecule.
- Each bond is represented by a single line.
- This is different from a chemical formula which only shows the number and type of atoms.
- Displayed formulae are useful for showing the structure of more complex molecules.
Examples of displayed formulae
- Water (H2O) has 2 hydrogen atoms and 1 oxygen atom.
- The oxygen atom is at the centre, with a single bond to each of the hydrogen atoms.
Examples of displayed formulae 2
- Ethane (C2H6) contains two carbon atom and six hydrogen atoms.
- They are connected by seven single bonds:
- A line between the two carbon atoms
- Six single lines between the carbon and each hydrogen atom
Interpreting a displayed formula
- A displayed formula helps:
- Identify the atoms: Count how many of each type of atom are present
- Identify the bonds: Count the number of bonds to see how the atoms are linked
- For example, using the displayed formula for methane (CH4) shows one carbon atom and four hydrogen atoms, connected by four single bonds.
- This makes it easier to see differences between similar molecules.
Test yourself on Formula of a Molecule
Which statement best describes a molecular formula?