Stoichiometry

• Valency

  The amount of electrons an atom has to gain or lose in order to achieve a full outer shell
• Valency

  • Groups 1-3 (metals) will LOSE electrons
  • Groups 5-7 (non-metals) will GAIN electrons
  • Group 4 can do either
• Ion

  An atom that has lost or gained electrons, resulting in a charge
• Determining chemical formula

  1. Know the valencies of the atoms

  2. Swap the numbers around

  3. Cancel out if valencies are equal
• Word equation

  Chemical equation written in words
• Symbol equation

  Chemical equation represented by symbols, must be balanced
• Balancing chemical equations

  1. Ensure same number of each type of atom on both sides

  2. Cannot change original chemical formula

  3. Add numbers in front of reactants/products
• State symbols

  Represent the physical state of reactants/products
• Mole

  6.02 x 10^23 atoms, molecules or ions of a substance
• Mole equations

  • Moles = Mass / Relative formula mass
  • Volume = Moles x 24 dm3/mol
  • Concentration = Moles / Volume
• Relative formula mass (Mr)


  Sum of all the different relative atomic masses (Ar)
• Calculating mass from moles

  1. Write balanced equation

  2. Calculate moles of reactant

  3. Calculate moles of product

  4. Calculate mass of product
• Calculating volume from moles

  1. Calculate moles of gas

  2. Use mole equation 2 to find volume
• Calculating volume from mass

  1. Calculate moles of gas

  2. Use mole equation 2 to find volume
• Calculating volume of reactant from volume of product

  1. Use balanced equation to find mole ratio

  2. Calculate moles of reactant

  3. Use mole equation 2 to find volume of reactant
• Calculating percentage yield

  Actual yield / Theoretical yield x 100
• Calculating percentage purity

  Mass of pure substance / Total mass x 100
• Empirical formula

  Simplest whole number ratio of atoms in a compound
• Molecular formula


  Actual number and type of atoms in a compound