1. Elements and compounds Grade 9

2. Definition of an element An element is a substance that cannot be made into anything simpler by means of a chemical reaction. The atoms of an element all have the same numbers of protons. There are over a hundred different elements and they are arranged in the periodic table.

3. Definition of a compound Compounds contain more than one element. The elements in a compound are not just mixed together: they are joined by strong forces called chemical bonds. You will not find any compounds in the periodic table. Compounds do not have the same properties as the elements they contain. A compound is a substance that can be made into something simpler by means of a chemical reaction.

4. Sodium metal is very reactive Chlorine is a poisonous gas. They combine to form sodium chloride which has different properties. It is non poisonous and non reactive.

5. Why do elements form compounds Atoms tend to have the maximum number of electrons in their outer levels. They achieve this by bonding with other atoms. Electron will move from Na to Cl

7. Ionic Compound An ionic compound is made up from metals and non metals. The metal will be written before the non metal. CaF 2 MgO NaCl K 2 S

8. Naming Ionic compounds The name of the metal will not change The name of the non metal will change into the “ root of the word + ide ” Oxygen will change into oxide Sulphur will change into sulphide Chlorine will change into chloride

9. Naming Ionic compounds CaO calcium oxide KCl Potassium chloride FeS Iron sulphide MgS Magnesium sulphide Al 2 O 3 Aluminium oxide