C3.1

• Chemical symbol


  Used to write the formulae of elements and simple covalent and ionic compounds
• Writing formulae for simple ionic compounds

  Balance the charges of the ions involved
• Writing formulae for simple covalent compounds

  Imagine what the ion would be, e.g. H2O balances - because the ions would be 2H+ and O2- (and ++ cancels out with -)
• Balanced chemical equation


  Count up how many atoms of each element you have on both sides of the equation, use large numbers e.g. 3H2O to balance the equation so that there is the same amount of each element on each side
• Use the names and symbols of common elements from a supplied periodic table to write formulae and balanced chemical equations where appropriate
• Ion


  Atoms of elements that have either lost or gained one or more electrons
• Atoms form ions in order to have a stable arrangement of electrons - i.e. one similar to that of a noble gas, with 8 electrons in its outer shell
• Group 1 ions


  Have a 1+ charge to gain the arrangement of a group 8 / group 0 (noble gas)
• In a compound, the charges of ions have to balance out, e.g. HCl exists because of the formation of an H+ ion and a Cl- ion, also H2SO4 exists because of the formation of 2H+ ions and a SO42- ion
• Common ions


  • Group 1: form 1+ ions
  • Group 2: form 2+ ions
  • Group 3: form 3+ ions
  • Group 5: form 3- ions
  • Group 6: form 2- ions
  • Group 7: form 1- ions
  • Ions from common acids: NO3- (nitric acid), Cl- (hydrochloric acid), SO42- (sulfuric acid)
• Constructing balanced ionic equations (HT only)

  1. Write out the full chemical equation

  2. Split (aq) substances up into ions e.g. HCl(aq) becomes H+(aq) + Cl-(aq) and write out as another equation

  3. Cancel out 'spectator ions' - unchanged ions on either side of the chemical equation

  4. You are now left with the ionic equation
• State symbols


  (s) solid, (l) liquid, (g) gas, (aq) aqueous
• Mole


  Amount of substance, the number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant: 6.02 x 10^23 per mole
• Relative formula mass


  The mass of one mole of a substance in grams is numerically equal to its relative formula mass
• One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance
• Converting between moles and grams

  Use the triangle: Moles = Mass / Relative formula mass
• Law of conservation of mass


  No atoms are lost or made during a chemical reaction so the mass of the products = mass of the reactants
• Chemical reactions can be represented by symbol equations, which are balanced in terms of the numbers of atoms of each element involved on both sides of the equation
• Mole


  One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance
• The Mr of nitrogen gas (N2) is 28 (2 x 14), so one mole is 28g
• Converting between moles and grams

  1. Mass / Mr = Moles

  2. Mass = Moles x Mr
• If a reaction appears to involve a change in mass - check to see if this is due to a reactant or a product as a gas and its mass has not been taken into account
• When a metal reacts with oxygen - mass of metal oxide product > mass of metal started with
• Stoichiometry


  The balancing numbers in front of compounds/elements in reaction equations
• Calculating stoichiometry from masses of reactants and products

  1. Convert masses in grams to amounts in moles (moles = mass/Mr)

  2. Convert the numbers of moles to simple whole number ratios
• Limiting reactant


  The reactant that is used up / not in excess, which limits the amount of products
• If a limiting reactant is used, the amount of reactant in excess that actually reacts is limited to the exact amount that reacts with the amount of limiting reactant you have
• Calculating masses of reactants or products using a balanced equation

  1. Find moles of the substance you're given the mass of: moles = mass / molar mass

  2. Use balancing numbers to find the moles of desired reactant or product

  3. Mass = moles x molar mass (of the reactant/product)