chemistry paper 1

• what is an element?

  a substance with only one type of atom
• what is a compound?

  a substance with two or more different atoms that are chemically bonded
• what is a mixture?


  different substances that are not chemically bonded
• what are the different methods to separate mixtures?

  - filtration which removes insoluble particles

  - evaporation

  - chromatography which separates substances

  - distillation or fractional distillation which condenses evaporated solvent
• what is the history of the atomic model?

  - ancient greeks thought that matter was invisible particles

  - jj thomson created the plum pudding model, which showed an atom to be a ball of positive charge with negative electrons around it

  - ernest rutherford found the nucleas was small and positively charged because of the gold leaf experiment

  - niels bohr discovered that electrons exist in shells

  - james chadwick discovered that the nuclease must contain neutrons with the protons
• what are the relative charges of the subatomic particles?


  proton is +1, neutron is 0 and electron is -1
• what are the relative masses of the subatomic particles?


  proton is 1, neutron is 1, electron is negligible
• what do the different numbers of an atom represent on the periodic table?

  the bigger number is the relative atomic mass (protons and neutrons) and the smaller number is the atomic number (protons which is equal to electrons)
• what is an isotope?

  the same element with the same number of protons and electrons but different number of neutrons
• how did mendeleev organise the periodic table?

  he ordered them by atomic weight and grouped elements based on their properties. he left gaps for elements that were later discovered.
• how is a positive ion formed?

  when an atom loses an electron
• how is a negative ion formed?

  when an atom gains an electron
• describe the properties of the alkali metals

  - form positive ions

  - more reactive as you go down the group

  - outer electron is further away from the nucleas

  - electrostatic attraction weakens

  - donates electron easier
• describe the properties of the halogens

  - form negative ions

  - less reactive and boiling point increases as you go down the group
• describe the properties of the noble gases

  - unreactive due to their full outer shell

  - low boiling points
• what are transition metals able to do?

  transfer different amount of electrons, e.g ironII and ironIII
• what happens in metallic bonding?

  a lattice of ions is formed and it is surrounded by delocalised electrons. the electrons are free to move through the lattice and can carry electrical charge, hence why metals are good conductors
• what happens in ionic bonding?

  metals donate to non-metals to form ions, so the metal ends up with an empty outer shell while the non-metal ends up with a full outer shell. their charges add up to 0
• ionic structures

  - arranged in a lattice of positive and negative ions to form a crystal

  - high melting and boiling points due to the strong ionic bonds and electrostatic forces

  - can conduct electricity when dissolved/molten since the ions are free to move and carry charge

  - positive ions are cations

  - negative ions are anions
• what happens in covalent bonding?

  a pair of electrons are shared between non-metals for a full outer shell
• why do simple covalent structures have low boiling points

  the weak intermolecular forces
• what happens in giant covalent bonding?

  repeating units of atoms make giant molecules, like diamond or silica. they have very high melting points due to having to break the strong covalent bonds
• what are the properties of graphite?

  - delocalised electrons form weak bonds

  - able to conduct electricity due to electrons moving freely

  - layers slide over each other
• how do you calculate concentration?

  moles/volume, units are mol/dm^3
• how do you concert cm into dm?

  divide by 1000
• what is percentage yield?

  the mass of products made in reality compared to the theoretical yield
• what is atom economy?

  how much desired product is made compared to the total reactant mass
• how do you calculate atom economy?

  mr of desired products/total mr of reactants x 100
• how do you calculate percentage yield?

  total mass of products/total mass of reactants x 100
• what is a displacement reaction?

  when a more reactive metal displaces a less reactive metal in a compound
• what is displacement used for?

  obtaining metals from their ores by displacing with a more reactive and less valuable metal or with carbon
• what happens in neutralisation?

  acid + alkali -> salt = water
• plan out a practical for titration

  - measure 50cm^3 of alkali with a glass pipette and put it into a conical flask with an indicator

  - put acid into a burette to the 0cm^3 mark. open the tap and let it drip into the conical flask

  - once the solution in the flask turns pink, stop and swirl. if it stays pink, the solution has been neutralised
• what is electrolysis of molten compounds?

  passing an electrical current through a substance for oxidation and reduction at electrodes
• what happens at the cathode?

  positive ions are attracted and they are reduced
• what happens at the anode?

  negative ions are attracted and they are oxidised
• why does the graphite anode need to be replaced frequently?


  the oxygen produced by the graphite reacts with the anode to produce carbon dioxide
• what happens during electrolysis of solutions?

  a more reactive cation stays in the solution while the less reactive is reduced at the cathode
• what happens if an anion is not a halide?

  oxygen will be produced
• how can you tell is a reaction is exo/endothermic?

  exothermic will get hot, while endothermic gets cold