Compounds

Compounds are pure substances that are composed of two or more elements chemically combined. The compound may have different properties to the elements that it is made from.

Water is a compound made when the colourless gas hydrogen reacts with oxygen, which is also a colourless gas. Water is a colourless liquid at room temperature.

Common table salt, is called sodium chloride. It is produced when sodium, a silvery metal reacts with chlorine, a yellow-green poisonous gas. Sodium chloride is a white crystalline solid.

Many of the substances that we use daily are compounds, some examples are shown below:

Compound	Properties	Uses
Sugar (sucrose)	Sweet white crystals	To sweeten food and drink
Marble (calcium carbonate)	White solid 'rock' material	Building material
Sulfuric acid (hydrogen sulfate)	Colourless oily liquid	Car batteries Used to make fertilisers

Activity:

Burn a piece of magnesium in the Bunsen flame.

Warning: Do not look directly at the piece of magnesium when it is burning. Look at it out of the corner of your eye.

The compound formed is magnesium oxide. It is made from the reaction between magnesium, which is a shiny metal and oxygen which, is a colourless gas. Describe the compound magnesium oxide. How is it different from the elements that it is made from?