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• in an element all the atoms are the same
• compounds contain two or more elements chemically combined in fixed proportions
• compounds usually have different properties from the elements they were made of
• mixtures are different elements and or compounds not chemically bonded together
• to separate a mixture you could us

  • filtration
  • distillation
  • crystallisation
  • chromotography
• a molecule has any elements chemically combined
• a chemical formula tells us the elements in a molecule and the numbers of atoms of each element
• physcial seperation techniques can only be used to separate mixtures
• filtration is used to separate an insoluble solid from a liquid
• insoluable means that the solid will not dissolve in the liquid
• to filter something we use a filter funnel and filter paper on top of a conical flask, we pour the mixture into the filter paper and the liquid passes through the tiny pores in the filter paper called the filtrate the solid material is trapped so in the end the liquid is separated from the solid
• crystallisation is used to separate a soluble solid from a liquid
• we can make crystallisation happen faster by gently heating our solution to evaporate the water however sometimes certain chemicals break down when we heat them so it is better to allow the water to evaporate on its own
• simple distillation consists of two stages

  • evaporate the liquid by heating which turns it into water vapour
  • we condense the vapour back to a liquid by cooling
• to do fractional distillation we place our solution with the liquid and dissolved solid into the flask which is connected to a continuous glass tube which is surrounded by a condenser where cold water from a tap continuously runs from it so the internal glass tube is cold, we also have a thermometer as part of the apparatus
• during simple distillation we start by heating our solution as we heat it the liquid starts to evaporate turning into a vapour which rises up the glass tube which passes through the thermometer where the reading increases, next the vapour passes into the condenser which causes the vapour to turn back into a liquid as it goes through collecting in a beaker so in the end we are left with crystals of our solid in the flask and the liquid in the beaker
• simple distillation can be used to create drinking water from sea water however it needs a great deal of energy so other techniques are used instead
• in fractional distillation we separate a mixture of different liquids however they must have different boiling points
• the apparatus for fractional distillation is similar to simple but with a fractionating column
• fractional distillation works by gently heating the mixture so the liquid with the lower boiling point evaporates more easily as two different vapours make their way into the fractioning column where they condense and drip back to the flask where they evaporate again, this repeated evaporation increases the amount of the lower boiling point chemical in the fractioning column, the mixtures pass the thermometer and condense back to a liquid. When the thermometer stops rising that means it is the lower of the two boiling points so the first mixture goes into the beaker.
• When the temperature starts to rise again a mixture of vapours is passing into the condenser mainly containing the chemical with the higher boiling point and when the thermometer reaches a constant temperature we are now collecting a relatively pure sample of the second chemical
• if the two liquids have very similar boiling points then it is much harder to separate them and we might need to carry out several rounds of fractional distillation

  the equipment used to smaller rounds is not useful for separating a very large volume of liquid such as crude oil
• all separation techniques are physical processes so they do not involve chemical reactions and no new substances are made
• paper chromatography allows us to separate our substances based of their different solubilities
• we take a piece of chromatography paper and we draw a pencil line near the bottom of the paper next we put a dot of our first colour on the pencil line and next to it our second colour, we place the bottom of the paper into a solvent the solvent makes it way up the paper which dissolves the ink in the dots so the ink is carried up the paper dissolved in the solvent
• the paper is the stationary phase as it does not move

  the solvent is the mobile phase as it does move
• If there is only a single spot of ink it means that it is a single pure colour if there is different numbers of dots that means the colour was a mixture
• a pure compound will produce a single spot in all solvents, while a mixture will produce a range of spots
• paper chromatography works because different substances have different solubilities, a more soluble substance is more attracted to the mobile phase than a less soluble substance
• if we drew the starting line in pen then the ink could dissolve in the solvent and move up the paper
• the ancient Greeks believed that everything was made up of atoms and they were tiny spheres which cannot be divided

  in 1897 scientists discovered that atoms contain tiny negative particles called electrons which meant that atoms must have an internal structure they used the plum pudding model instead where the atom is a ball of positive charge with negative electrons embedded in it
• the alpha scattering experiment was done by Ernest Rutherford and his team in 1911 he told a piece of gold foil then fired tiny particles at it called alpha particles which have a positive charge they found that most passed straight through which changing direction but sometimes it was deflected or bounced straight back which told us that atoms are mainly empty space with a centre that had a positive charge and had a great deal of mass so scientists replaced the plum pudding model with the nuclear model
• niels bohr proposed that electrons orbit the nucleus at specific distances as they contained shells

  after that scientists found that the positive particles were in the nucleus and called protons and the number of protons determines the amount of positive charge in the nucleus

  James Chadwick discovered that the nucleus also contained neutral particles which were called neutrons
• relative charges

  proton - +1

  neutron - 0

  electron -1
• atoms have no overall charge since the number of electrons is the same as the protons
• relative mass

  proton - 1

  neutron - 1

  electron - very small
• the atomic number tells us the number of protons and electrons in an element the mass number is that take away the protons in order to find the neutrons
• isotopes are atoms of the same element with different numbers or neutrons
• ions are atoms which have an overall charged because ions have lost or gained electrons
• positive ions lost electrons while negative ions have gained electrons