AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Compounds are formed from elements by chemical reactions.
Full specification wording
Atoms, elements and compounds: Compounds are formed from elements by chemical reactions.
A compound is a substance made of two or more different elements chemically combined in fixed proportions.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 4 of 10
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A compound is a substance made of two or more different elements chemically combined in fixed proportions. Compounds are formed when elements react together, and the reaction involves the formation of chemical bonds between atoms. For example, sodium reacts with chlorine to form sodium chloride, and hydrogen reacts with oxygen to form water. The properties of a compound are different from those of its constituent elements. Compounds can be represented by chemical formulae, such as NaCl or H₂O. The statement emphasises that chemical reactions are required to form compounds from elements, and that the elements are chemically bonded, not just mixed. This distinguishes compounds from mixtures, where components are not chemically combined and can be separated by physical means.
What earns the marks
- Define a compound as a substance formed from two or more elements chemically combined.
- State that compounds are formed by chemical reactions.
- Recognise that the elements in a compound are in fixed proportions.
- Explain that the properties of a compound differ from those of its constituent elements.
- Write chemical formulae for simple compounds.
Common mistakes and how to put them right
Confusing compounds with mixtures.
Put it right: Compounds are chemically combined and have fixed composition.
Thinking that compounds can be separated by physical means.
Put it right: Use chemical methods.
Believing that the properties of a compound are the same as its elements.
Put it right: Give examples like sodium chloride vs sodium and chlorine.
Exam tips
- When explaining the formation of a compound, mention chemical reaction and chemical bonding.
- Use examples such as water (H₂O) or carbon dioxide (CO₂) to illustrate compounds.
- Distinguish clearly between compounds and mixtures in your answers.
Try the lesson
The start of the Atoms, elements and compounds: Compounds are formed from elements by chemical reactions. lesson, made from checked teaching notes for this specification point.
Have a go first
How are compounds formed from elements?
Listen
A compound is a substance made of two or more different elements chemically combined in fixed proportions. Compounds are formed when elements react together, and the reaction involves the formation of chemical bonds between atoms. For example, sodium reacts with chlorine to form sodium chloride, and hydrogen reacts with oxygen to form water. The properties of a compound are different from those of its constituent elements. Compounds can be represented by chemical formulae, such as NaCl or H₂O. The statement emphasises that chemical reactions are required to form compounds from elements, and that the elements are chemically bonded, not just mixed. This distinguishes compounds from mixtures, where components are not chemically combined and can be separated by physical means. A strong answer earns marks for these points. Define a compound as a substance formed from two or more elements chemically combined. State that compounds are formed by chemical reactions. Recognise that the elements in a compound are in fixed proportions. Explain that the properties of a compound differ from those of its constituent elements. A common slip: Confusing compounds with mixtures: a mixture contains substances not chemically combined. Instead, compounds are chemically combined and have fixed composition. Exam tip: When explaining the formation of a compound, mention chemical reaction and chemical bonding.
See it
Key words
Say what each word means before you turn the card.
Compound
Try answering aloud or in your head before turning the card.
Chemical reactions
Try answering aloud or in your head before turning the card.
Chemical formulae
Try answering aloud or in your head before turning the card.
Mixtures
Try answering aloud or in your head before turning the card.
See every definition
- Compound
- A substance made of two or more different elements chemically combined in fixed proportions.
- Chemical reactions
- The process by which compounds are formed from elements, involving the formation of chemical bonds between atoms.
- Chemical formulae
- A way of representing compounds, such as NaCl or H₂O.
- Mixtures
- Components that are not chemically combined and can be separated by physical means.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Atoms, elements and compounds: Compounds are formed from elements by chemical reactions.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge