Compounds and Mixtures

Compounds and Mixtures

1. Elements and Compounds

   • An element contains only one type of atom.
   • A compound contains different types of atoms joined together.
   • The formula of a substance tells us the number of each type of atom present in the substance.
   • The properties of a compound are different from those of the elements which it contains.
   • A compound is a pure substance which is made of the same particles.
   • A sample of a compound will always have the same elements present in the same fixed proportions.

2. Compounds and Mixtures

   • Compounds will react chemically to make new substances.
   • You can tell that a compound has reacted by observing what happens to it.
   • A mixture is formed when two or more substances are added together.
   • Air is a mixture of gases that can be separated into pure substances.
   • Air consists of nitrogen, oxygen, argon (and other noble gases), carbon dioxide and water vapour.
   • Each of the gases found in air has important uses.
   • Air can be liquefied and then individual gases can be separated by fractional distillation.
   • Sea water and mineral water are other examples of mixtures.

3. Elements and Mixtures

   • Elements and compounds melt and boil at a certain temperature.
   • Mixtures do not melt or boil at one particular temperature.
   • The melting point and boiling point of a mixture change as the composition of the mixture changes.