paper 2

• isotopes have the same number of protons and a different number of neutrons
• RAM is the mean mass of the atoms of an element relative to 1/12 of the mass of a Carbon-12 atom
• Ionic bonds:

  • strong electrostatic forces of attraction between oppositely charged ions
  • has a regular lattice structure
  • happen between a metal and a non-metal
  • high melting and boiling points because of the strong ionic bonds and large amounts of energy that must be transferred to break the bonds
  • Often soluble in water- dissolve to form aqueous solutions
• Covalent bonds:

  • strong
  • form between non-metals
  • often produce molecules
  • simple and giant
• simple molecular:

  • a few atoms joined by strong covalent bonds
  • made of non-metal compounds or elements
  • low melting and boiling points
  • do not conduct as electrons are not free to move
  • most are insoluble
• giant molecular:

  • joined by strong covalent bonds in a regular lattice structure
  • high melting and boiling points
  • insoluble

  Diamond:

  • each atom is bonded to four others, which makes it very strong and means it cannot conduct electricity

  Graphite:

  • each atom is bonded to three others
  • weak intermolecular forces between layers
  • Strong covalent bonds between atoms in a layer
• Graphene:

  • same structure as a single layer of graphite
  • each atom is bonded to three others in a regular lattice structure
  • outer electrons are delocalised meaning it can conduct electricity

  Fullerenes:

  Buckyballs:

  • can conduct because they have delocalised electrons
  • Are soft when solid because they have weak intermolecular forces

  Nanotubes:

  • can conduct because they have delocalised electrons
  • are very strong because the structure has many strong covalent bonds
• metals vs non-metals:

  • metals: shiny, good conductors, high density, high melting point, malleable
  • non-metals: dull, poor conductors, low density, low melting point, brittle
• metallic bonds:

  • giant lattice of positively charged metal ions
  • sea of delocalised electrons
• empirical formula:

  1. write down mass of each element
  2. write down atomic mass of each element
  3. mass/ Ar
  4. Divide by smallest number
  5. Write as a ratio
• Conservation of mass:

  • Closed system: nothing can enter or leave
  • precipitation reaction: two soluble reactants form an insoluble product
  • Non-enclosed system: substances can enter or leave
  • mass of a reactive metal increases if heated in air because oxygen atoms combine with metal atoms for form a metal oxide
  • mass of a reactive non-metal decreases if heated in air because products which are gas escape from the container
  • mass of metal carbonate decrease if heated because CO2 gas is produced and escapes from container
• Concentration of solutions:

  • a solution is a mixture of a solute in a solvent
  • solute is the substance that dissolves
  • Solvent is the substance that the solute dissolves in
  • 1 dm^3 = 1000 cm^3
  • concentration = mass of solute/ volume of solution
  • concentration is measured in g dm^3
• Moles:

  • mole: the amount of a substance in a given volume
  • Avogadro's constant: 6.02 x 10^23
  • moles= mass / relative atomic mass
• Gas tests:

  hydrogen: lit splint squeaky pop

  oxygen: relights glowing splint

  carbon dioxide: turns limewater cloudy

  chlorine: bleaches damp blue litmus paper
• Group 1: Alkali metals

  • good conductors of heat and electricity
  • shiny when freshly cut
  • are soft (can cut through with a knife)
  • have relatively low melting points, but are all solid
  • react with water to produce an alkaline metal hydroxide
  • reactivity increases down the group
• Lithium:

  • fizzes steadily
  • is less dense than water- floats
  • stored in oil to keep water and air away

  Sodium:

  • melts into a ball from heat released in the reaction and fizzes rapidly
  • is less dense than water- floats
  • stored in oil to keep water and air away

  Potassium:

  • gives off sparks and hydrogen produced burns with a lilac flame
  • is less dense than water- floats
  • stored in oil to keep water and air away
• Group 7- Halogens:

  • melting and boiling points increase down the group
  • intermolecular forces between molecules are stronger down the group (more heat energy needed to overcome forces)

  Chlorine:

  • gas at room temp
  • yellow-green

  Bromine:

  • liquid at room temp
  • red-brown

  Iodine:

  • solid at room temp
  • dark grey (purple vapour when warmed)
• Reactions of halogens:

  • halogens react with metals to produce compounds called metal halides
  • they gain electrons and are reduced
• displacement reactions can be demonstrated by adding a halogen solution to a metal halide solution then seeing if the mixture darkens.

  • chlorine in "chlorine water" displaces bromine from aqueous sodium bromide solution
• Group 0- Noble gases:

  • chemically inert- have full outer shells of electrons so cannot lose or gain electrons
  • Helium --> balloons (non-flammable, less dense than air)
  • Argon, krypton, xenon --> filament lamps (gets hot enough to glow)
  • argon --> shield gas (keeps air away from metal because it is more dense than air)
• Rates of reaction:

  • Concentration/pressure: increases the amount of particles in the same volume, increasing rate of reaction
  • SA:V ratio: when increased, there are more particles of reactant available, increasing frequency of successful collisions
  • Temperature: increases rate of reaction because particles gain energy so frequency of collisions increases

  Activation energy: minimum energy needed by reactant particles for a reaction to happen
• Investigating rates:

  1. prepare 3 sets of marble chips on folded paper, one for each size of chips. Adjust numbers until they all have same mass
  2. add measured volume of dilute acid to conical flask.
  3. plug flask with cotton wool
  4. place flask and one set of chips on balance and record reading
  5. remove cotton wool and add chips to acid
  6. start stop clock and replace cotton wool
  7. Record mass every 30s for a few minutes
  8. repeat with other sets of chips
• Temperature changes:

  • exothermic= heat energy give out, mixture/ surroundings increase in temperature
  • endothermic= heat energy taken in, mixture/ surroundings decrease in temperature
  • breaking bonds is endothermic - energy is needed
  • making bonds is exothermic - energy is released
• Changes in heat energy:

  • neutralisation: exothermic, endothermic
  • displacement: exothermic
  • precipitation: exothermic, endothermic
  • dissolving: exothermic, endothermic
• hydrocarbons are compounds that contain carbon and hydrogen only, that are made up of covalent bonds
• crude oil is a complex mixture of hydrocarbons containing molecules in which carbon atoms are in chains or rings. It is an important source of useful substances and a finite resource
• Crude oil can be separated by fractional distillation because its different hydrocarbons have different boiling points.

  1. oil is heated to evaporate it
  2. vapours rise in a fractionating column with a temperature gradient (hot at the bottom, cool at the top)
  3. each fraction condenses where it becomes cool enough, and is piped out of the column

  • gases fraction doesn't condense and leaves at the top
  • bitumen fraction doesn't evaporate and leaves at the bottom
• • gases, used in domestic heating and cooking
  • petrol, used as fuel for cars
  • kerosene, used as fuel for aircraft
  • diesel oil, used as fuel for some cars and trains
  • fuel oil, used as fuel for large ships and in some power stations
  • bitumen, used to surface roads and roofs
• • alkanes are a homologous serious of hydrocarbons
  • they have only single bonds, are flammable and form carbon dioxide and water during complete combustion