1. 5.1Substances in the Earth’s crust The Earth’s crust consists of many different substances.

2. 5.2What is a compound? A compound is a substance containing two or more elements chemically joined together.

3. 5.3Making and breaking the compound water When hydrogen combines with oxygen to form the compound water, a lot of energy is given out.  Hydrogen + oxygen water Electrical energy can be used to break down water into hydrogen and oxygen.  Water hydrogen + oxygen  Electrical energy video 5.3

4. 5.4What is a mixture? A mixture contains two or more elements or compounds not chemically joined together.

5. 5.5Comparing properties of carbon/oxygen mixture and carbon dioxide

6. Molecule ( 分子 ) Some atoms can join together to form a group called a molecule. Molecule of an element Molecule of a compound

7. 5.5Comparing properties of carbon/oxygen mixture and carbon dioxide When carbon and oxygen are mixed together without heating, the carbon atoms and oxygen molecules are still present in the mixture. When carbon is heated in oxygen, carbon atoms and oxygen atoms join together to form carbon dioxide molecules. The carbon dioxide molecules are different from the carbon atoms and oxygen molecules. Properties of carbon dioxide are different from those of carbon and oxygen. ani 5.5

8. 5.6Comparing properties of iron/sulphur mixture and iron(II) sulphide Iron and sulphur still retain their original properties in the mixture. However, when they combine to form a compound, the compound shows new properties.

9. Comparing properties of hydrogen/oxygen mixture and water Appearance Hydrogen : colourless gas Oxygen : colourless gas Water : colourless liquid

10. Comparing properties of hydrogen/oxygen mixture and water(chemical properties) Inserting a burning splint Hydrogen : a ‘pop’ sound Oxygen : burn more violently Water : extinguish the fire

11. 5.7Useful web links Materials on mixtures  http://library.thinkquest.org/3659/atommole http://library.thinkquest.org/3659/atommole Comparison of mixtures and compounds  http://www.chem.vt.edu/RVGS/ACT/notes/Mixtures_and_Compounds.html http://www.chem.vt.edu/RVGS/ACT/notes/Mixtures_and_Compounds.html