Elements, Compounds and Mixtures

• what is an element?

  an element is a pure substance which cannot be split into simpler substances by any chemical process.
• There are 103 elements
• An element may consist of individual atoms of the same kind, e.g. copper Cu2, or molecules composed of atoms of the same kind, e.g. oxygen O2
• Metals

  Lithium Li

  Sodium Na

  Potassium K

  Uranium U

  Lead Pb

  Tin Sn

  Aluminium Al

  Beryllium Be

  Magnesium Mg

  Calcium Ca

  Barium Ba
• Compounds are...

  a substance containing two or more different types of element bonded together chemically in fixed proportions and in such a way that their properties are changed.
• magnesium (element) + oxygen (element) = magnesium oxide (compound)
• compounds may be represented by chemical formulae.
• Mixtures...

  a mixture consists of two or more substances combined together physically.
• Mixtures can be classified as:

  1. solution
  2. suspension
  3. colloid
• Heterogeneous mixtures...

  a heterogeneous mixture is a non-uniform mixture. e.g. suspensions and colloids.
• Homogeneous mixture is...

  a uniform mixture; it has the same composition and properties throughout the mixture. e.g. solutions
• solution

  this is formed when the solute is completely dissolved in the solvent e.g. sugar and water.
• solute

  is the substance to be dissolved
• solvent

  is the substance doing the dissolving.
• water is an excellent solvent
• suspension is...

  a heterogeneous mixture that contains solid particles that do not dissolve. e.g. sand and water
• colloids...

  colloid is a a homogeneous mixture. e.g. milk and water
• pure substance

  a pure substance consist of only one type of material
• Pure substances have fixed melting and boiling points
• Impurities lower the melting point and raise the boiling point of a pure substance
• How do you find out if a substance is pure?

  Its melting or boiling point is determined