AQA - chemistry paper 1

• Substances are made of atoms, the different types of atoms are represented in the periodic table by a symbol
• Compound


  A substance that contains two or more different types of atoms chemically bonded together
• If there's no number after a symbol, there's an invisible 1
• Balancing chemical equations


  1. Start with atoms that are only in compounds

  2. Balance atoms that are in excess

  3. Finish balancing atoms that are elements
• Mixture


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


  • Air
  • Salt water
• Separating mixtures


  1. Filtration for large insoluble particles

  2. Crystallization for solute left after solvent evaporation

  3. Distillation for liquids with different boiling points
• States of matter


  • Solid - particles vibrate around fixed positions
  • Liquid - particles free to move past each other
  • Gas - particles far apart and move randomly
• Melting and evaporation are physical changes, not chemical reactions
• State symbols


  s for solid, l for liquid, g for gas, aq for aqueous (dissolved)
• Atomic models


  • Thompson's plum pudding model
  • Rutherford's discovery of the nucleus and mostly empty space
  • Bohr's discovery of electron shells
• Protons, neutrons, electrons


  • Protons and neutrons have a relative mass of 1, electrons have a very small mass
  • Protons and electrons have equal and opposite charges
• Periodic table


  • Bottom number is atomic number (protons)
  • Top number is mass number (protons + neutrons)
  • Isotopes have 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 in each shell
• Periodic table sections


  • Metals - left of staircase
  • Non-metals - right of staircase
  • Transition metals
• Group


  Column in periodic table, indicates number of electrons in outer shell
• Group properties


  • Group 1 - alkali metals, reactive
  • Group 7 - halogens, less reactive down group
  • Group 0 - noble gases, very unreactive
• Ions


  Atoms that have gained or lost electrons, have a charge
• Ionic bonding


  • Metal atoms donate electrons, non-metal atoms accept electrons
  • Ionic compounds have high melting/boiling points and can conduct electricity when molten or dissolved
• Covalent bonding


  • Non-metal atoms share electrons to gain full outer shells
  • Forms molecules with relatively low melting/boiling points
• Covalent molecules


  • Cl2, N2, CH4, H2O, CO2
• Giant covalent structures


  • Atoms form continuous networks of covalent bonds, like diamond and graphite
• Nanoparticles are between 100-2500 nm in size, smaller than dust particles
• 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
• Balancing a chemical equation

  Determine the number of moles of each reactant and product
• In the methane combustion reaction, we need 2 moles of oxygen per 1 mole of methane
• Stoichiometry


  The ratio of moles of one substance to another in a reaction
• Concentration of a solution can be expressed in moles per decimeter cubed (mol/dm^3)
• If 1 mol of HCl is dissolved in 1 dm^3 of water, the resulting solution has a concentration of 1 mol/dm^3
• 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