Chemistry Paper 1

• Balancing chemical equations


  1. Start balancing atoms that are only in compounds

  2. Can't change small numbers as that would change the compound

  3. Put numbers in front of elements or compounds to multiply them up

  4. Finish balancing elements that are not in compounds
• Mixture


  Any combination of any different types of elements and compounds that aren't chemically bonded together
• Solution


  A mixture of a solute dissolved in a solvent
• Separating mixtures


  1. Filtration for large insoluble particles

  2. Crystallization to leave solute behind after evaporating solvent

  3. Distillation to separate liquids with different boiling points
• Physical changes


  • No new substances are being made
  • Breaking intermolecular forces, not chemical bonds
• States of matter


  • Solid - particles vibrate in fixed positions
  • Liquid - particles can move past each other
  • Gas - particles move randomly and have high energy
• Gases can be compressed, solids and liquids cannot
• To melt or evaporate a substance, energy must be supplied to overcome intermolecular forces
• Atom models


  • Plum pudding model - positive charge with electrons dotted around
  • Nuclear model - positive nucleus with electrons orbiting relatively far away
• Atomic structure


  • Protons - positive charge, mass of 1
  • Neutrons - no charge, mass of 1
  • Electrons - negative charge, very small mass
• Periodic table


  • Atomic number - number of protons
  • Mass number - number of protons and neutrons
  • Isotopes - atoms of the same element with different numbers of neutrons
• Periodic table was developed by grouping elements based on their properties, not just atomic weight
• Electron configuration


  Electrons fill up shells around the nucleus, with a maximum of 2, 8, 8, 2 electrons per shell
• Periodic table sections


  • Metals - to the left of the staircase, donate electrons
  • Non-metals - to the right of the staircase, accept electrons
  • Noble gases - group 0, very unreactive
• Ion formation


  • Metals form positive ions by losing electrons
  • Non-metals form negative ions by gaining electrons
• Ionic bonding


  • Metal atoms donate electrons to non-metal atoms
  • Resulting ions are held together by electrostatic forces
  • Ionic compounds have high melting/boiling points and can conduct electricity when molten or in solution
• Covalent bonding


  • Non-metal atoms share electrons to fill their outer shells
  • Covalent compounds have relatively low melting/boiling points and cannot conduct electricity
• Giant covalent structures


  • Diamond - carbon atoms bonded in a giant crystal structure
  • Graphite - layers of carbon atoms with delocalized electrons between layers
• Nanoparticles are between 100-2500 nm in size, have a high surface area to volume ratio
• Conservation of mass


  Total mass of substances is conserved in a chemical reaction
• Mole


  A specific number of atoms or molecules, used to compare amounts of substances
• Mass is conserved in a chemical reaction
• Atoms that go in must come out, so we must balance equations
• Relative atomic mass (RAM)


  The mass of an atom relative to the mass of a carbon-12 atom
• Relative formula mass (RFM)


  The sum of the relative atomic masses of the atoms in a compound
• CO2 has a relative formula mass of 12 + 2 x 16 = 44
• Reactions can produce a gas product, which can result in a seeming decrease in mass of the reactants
• If you have as many grams of a substance as its relative atomic or formula mass, you have one mole
• Moles


  Calculated as mass (g) divided by relative atomic/formula mass (RAM/RFM)
• In the methane combustion reaction, we need two moles of oxygen per one mole of methane
• Calculating mass of product from mass of reactant

  Mass -> Moles -> Moles -> Mass
• The stoichiometry of a reaction is the ratio of moles of one substance to another
• Concentration of solutions can be given in g/dm³ or mol/dm³
• One mole of HCl dissolved in 1 dm³ of water makes 1 mol/dm³ hydrochloric acid
• Percentage yield is the actual amount of product made compared to the theoretical maximum
• Atom economy


  The percentage of the total mass of reactants that ends up in the desired product
• One mole of any gas takes up 24 dm³ at room temperature and pressure
• Reactivity series of metals

  • Hydrogen
  • Carbon
  • Most reactive metals
  • Least reactive metals
• Displacement reaction


  A more reactive metal displaces a less reactive metal from a compound
• Metals more reactive than hydrogen can displace it from acids