Atoms, elements and compounds

• Chemical symbols

  • Represent one atom of an element
  • Have one or two letters
  • eg Hydrogen-H or Magnesium-Mg
• Atom 


  The smallest part of an element that can exist
• Element

  A substance made of one type of atom only
• Chemical formulae of elements

  • The formulae for most elements is just their chemical symbol
  • Eg iodine-I2
• Molecule 


  A collection of two or more atoms held together by chemical bonds
• Compounds

  • Two or more elements that are chemically combined
  • they are presented in fixed proportions
  • Eg MgO- magnesium oxide
• Compound

  A substance formed by chemical union of two or more elements
• Word equations

  • Shows the name of the substances involved in a reaction
  • Reactants are on the left of the arrow
  • products are on the right of the arrow
• Balanced chemical equations

  • A balanced equation has the same number of atoms of each element on both sides of the arrow