Elements and compoundsElements and compounds

Grade 9

Definition of an elementDefinition 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.  

Definition of a compoundDefinition 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.  

• 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.

Why do elements form compoundsWhy 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

Ionic CompoundIonic Compound

• An ionic compound is made up from metals and non metals.

• The metal will be written before the non metal.

• CaF2 MgO NaCl K2S

Naming Ionic compoundsNaming 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

Naming Ionic compoundsNaming Ionic compounds

• CaO • calcium oxide• KCl• Potassium chloride• FeS• Iron sulphide• MgS• Magnesium sulphide

• Al2O3

• Aluminium oxide