One or two letters used to represent a chemical element. The first letter is always a capital letter, e.g. Br represents bromine.

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

Chemical formulae

Science

Atoms and elements

Properties of elements

Metallic elements

Molecular elements

Common elements

Compounds and their formation

Naming compounds

A particle model of chemical reactions

In the Understanding Chemical Reactions unit, pupils will build on their knowledge of atoms, elements, and compounds to learn about how atoms rearrange to form new substances during chemical reactions.

In the Solid, Liquid and Gas States and Changes of State unit, pupils learned to categorise substances and understand particle behaviour during changes of state.

This unit explores the basic atomic model, the differences between atoms, elements, and compounds, and the varying physical and chemical properties of elements. It covers chemical symbols, formulae, SI units, and IUPAC nomenclature, emphasising their use in describing elements and compounds.

Atoms, elements and compounds

Two hydrogen molecules and one oxygen molecule.

What does the chemical formula H₂O represent?

The compound is twice as heavy as oxygen.

In the formula CO₂, what does the subscript '2' indicate?

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 ...

There's no difference. They have the same number of oxygen and hydrogen atoms.

What is the difference between H₂O and H₂O₂?

A graphical representation of a molecule.

A symbolic way to represent the elements in a chemical substance.

A method to determine the pH of a substance.

Which statement best defines a chemical formula?

Match the following chemical substances up to the key terms.

Which element does the chemical symbol 'O' represent?

In the chemical formula CO₂, what element does 'C' represent?

Match the chemical formula to the correct substance.

Each {{}} is represented by its own chemical symbol, for example 'K', 'Fe' or 'C'.

A substance that cannot be broken down into simpler substances.

Anything that has mass and takes up space.

A substance composed of only one chemical substance.

Two or more atoms bonded together (usually non-metals).

Two or more different types of atoms bonded together.

Match each term with its correct definition.

Exit Quiz

What does the chemical formula H₂O represent?