New
New
Chemical formulae
I can use chemical symbols to write down chemical formulae for elements and compounds.
Lesson 7 of 9
New
New
- Year 8
Chemical formulae
I can use chemical symbols to write down chemical formulae for elements and compounds.
Lesson details
Key learning points
- The symbols for each element (each type of atom) a substance contains, appear in its chemical formula.
- Numbers (subscripts) next to chemical symbols in a formula show the numbers of each type of atom in a compound.
- Each compound contains a different combination of elements.
- Some compounds contain the same elements as other compounds, but in a different ratio.
Keywords
Chemical symbol - One or two letters used to represent a chemical element. The first letter is always a capital letter, e.g. Br represents bromine.
Chemical formula - A representation of either the number of atoms or ratio of atoms of each element in a substance, e.g. H₂O is water = 2 x hydrogen + 1 x oxygen
Common misconception
Writing subscript values as superscript values.
Subscript values show the number of the atoms, while superscript in maths is used to square a value and so does not apply to chemical formulae.
Use many examples to show that superscript values are not correct, i.e. the element cannot be squared. Also model many examples of formulae, breaking down each element and how many atoms of each are present.
Teacher tip
Equipment
Licence
This content is © Oak National Academy Limited (2026), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Lesson video
Loading...
Prior knowledge starter quiz
6 Questions
Q1.Which element does the chemical symbol 'O' represent?
Which element does the chemical symbol 'O' represent?
Q2.In the chemical formula CO₂, what element does 'C' represent?
In the chemical formula CO₂, what element does 'C' represent?
Q3.Which of the following is a molecule?
Which of the following is a molecule?
Na
Mg
Q4.Match the chemical formula to the correct substance.
Match the chemical formula to the correct substance.
Q5.Each is represented by its own chemical symbol, for example 'K', 'Fe' or 'C'.
Each is represented by its own chemical symbol, for example 'K', 'Fe' or 'C'.
Q6.Match each term with its correct definition.
Match each term with its correct definition.
Assessment exit quiz
6 Questions
Q1.What does the chemical formula H₂O represent?
What does the chemical formula H₂O represent?
One hydrogen atom and two oxygen atoms.
Two hydrogen molecules and one oxygen molecule.
Two oxygen atoms and one hydrogen atom.
Q2.In the formula CO₂, what does the subscript '2' indicate?
In the formula CO₂, what does the subscript '2' indicate?
There are two carbon atoms.
The compound is twice as heavy as oxygen.
The compound is twice as reactive.
Q3.It is important to write subscript values correctly, both in terms of the value, but also in their physical size and placement to accurately represent the correct number of each type of ...
It is important to write subscript values correctly, both in terms of the value, but also in their physical size and placement to accurately represent the correct number of each type of ...
Q4.What is the difference between H₂O and H₂O₂?
What is the difference between H₂O and H₂O₂?
H₂O₂ has more hydrogen atoms.
H₂O has more oxygen atoms.
H₂O has more hydrogen atoms.
There's no difference. They have the same number of oxygen and hydrogen atoms.
Q5.Which statement best defines a chemical formula?
Which statement best defines a chemical formula?
A description of a chemical reaction.
A graphical representation of a molecule.
A method to determine the pH of a substance.
Q6.Match the following chemical substances up to the key terms.
Match the following chemical substances up to the key terms.
