GCSE-ready- Home
- Lessons
- GCSE & IGCSE Chemistry
- Elements, compounds and mixtures
Elements, compounds and mixtures
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
Every substance is an element, a compound or a mixture. Melting and boiling points show whether it is pure.
Three kinds of substance
Element: made of only one type of atom (for example iron, oxygen).
Compound: two or more elements chemically combined in fixed proportions (for example water, H2O). It can only be separated by a chemical reaction.
Mixture: two or more substances not chemically combined (for example air, sea water). It can be separated by physical methods.
Compound: two or more elements chemically combined in fixed proportions (for example water, H2O). It can only be separated by a chemical reaction.
Mixture: two or more substances not chemically combined (for example air, sea water). It can be separated by physical methods.
Pure substances
A pure substance has a fixed melting point and boiling point.
Pure water melts at 0 °C and boils at 100 °C.
A mixture (impure substance) melts and boils over a range of temperatures. Impurities usually lower the melting point and raise the boiling point.
Pure water melts at 0 °C and boils at 100 °C.
A mixture (impure substance) melts and boils over a range of temperatures. Impurities usually lower the melting point and raise the boiling point.
Using the test
To check if a solid is pure, measure its melting point. A sharp melting point that matches the data book value means it is pure.
A white solid melts between 112 °C and 118 °C. Is it pure?
- A pure substance melts at one fixed temperature.
- This solid melts over a range of 6 °C.
Answer: No, it is a mixture (impure).
Elements contain one type of atom. Compounds are elements chemically combined in fixed proportions. Mixtures are not chemically combined and can be separated physically. Pure substances have fixed melting and boiling points.
Check you have got it
Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.