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Atoms and elements

  • An atom is made up of protons, neutrons, and electrons.
  • Electrons are around the outside, and are negativly charged.
  • Protons are positivly charged are are in the nucleus.
  • Neutrons are neutral, and are in the nucleus.
  • Overall atoms are neutral, due to the number of protons and electrons being the same in an atom.
  • Elements consists of one type of atoms only.

 

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The periodic table

  • Atoms of each element are represented by symbols.
  • Vertical columns are called groups.
  • All the elements in the same group have the same number of electrons in their outside shell., therefore they have similar properties.
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Electron shells

  • Electrons always fill the inner shells first.
  • only a certain number of electrons are allowed in each shell.

1st shell = 2         2nd shell = 8       3rd shell = 8

  • Atoms are more stable when they have a full outer shell.
  • Atoms react in order to fill their outer shell.
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Compounds

  • Atoms form chemical bonds with other atoms to form compounds. making it difficult to seperate the two elements again.
  • making bonds involves atoms giving away, taking, or sharing electrons.
  • Different types of bonding creates compounds.
  • Formulas show what atoms are in a compound.
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Balancing equations

  • There must always be the same number of atoms of each element on both sides.

1) Find an element that doesnt balence - Pencil in a number.

2) See where it gets you. It may create another imbalance - If so repeat 1.

3) Carry on chasing unbalenced elements until both sides are equal.

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Using limestone

  • Limestone is mainly calcium carbonate.
  • when it is heated it thermally decomposes to make calcium oxide and carbon dioxide.
  • Magnesium, copper, zinc, and sodium carbonates decompose in the same way.
  • Calcium carbonate + Acid --> calcium salt + carbon dioxide + water
  • calcium oxide + water --> Calcium hydroxide
  • Calcium hydroxide is an alkali, which can be used to nutralise acidic soil, or a make limewater which can test for carbon dioxide.
  • Limestone is heated in a kiln with powdered clay to make cement.
  • Cement can be mixed with sand and water to make motar, or sand and aggregate to make conctrete.
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Using limestone ii

  • Quarrying limestone destroys the landscape and habbitats around it. It produces a lot of noise and air pollution.
  • Energy is needed to produce cement and quicklime. the energy is likly to come from burning fossil fuels.
  • Chemicals used in dyes, paints, and medicines come from limestone.
  • acidity in lakes and rivers caused by acid rain can be nutralised with limestone products.
  • Limestone is widly available, hard wearing, and attreactive.
  • Conctete is cheap and a quick way of constructing buildings
  • Conctete is very unattractive.
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Limestone cycle

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getting metals from rock

  • A meatl ore is a rock which contains enough metal to make it worthwhile extracting the metal from it.
  • in mant cases the ore is an oxide of the meatal. For example the main aluminium ore is bauxite.
  • Most ores are extracte by a chemical reaction.
  • Economics effects metal extration.
  • Metals can be ectracted by reduction or electrolysis.
  • Some ores may have to be concentrated before the meatl is extracted.
  • Electrolysis can also be used to purify the extyracted metal.
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Reduction

  •  A metal can be extracted from its ore chemically by reduction using carbon.
  • When an ore is reduced the oxygen is removed.
  • the position of the metal on the reactivity series determines whether it can be extracted by reduction with carbon.

- Metal higher than carbon have to be extracted using electrolysis, which is expensive.

- Metals below carbon can be extracted by reduction using carbon. For example iron oxide is reduced in a blast furnace to make iron.

  • This is because carbon can only take the oxygen away from the metals which are les reactive than carbon itself.
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Electrolysis

  • Metals that are more reactive than carbon have to be extracted using electroysis of molten compounds.
  • This is more expensive because it uses a lot more energy due to the high temperatures required to melt the oxide so that the metal can be extracted.
  • Copper can be purified using electrolysis, so that it is able to conduct electricity.
  • Electrolysis is the breaking down of a substance using electricity.
  • it requires a liqid to conduct the electricity called the electrolyte. these are often metal salt solutions from the ore or molten metal oxides.
  • The electrolyte has free ions which conduct the electricity.
  • Electrons are taken aweay by the posotive anode and given away by the negative cathode. As ions gain or lose electrons they become atoms or molecules and are released.
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Displacement

  • If you put a reactive metal into a solution of a dissolved metal compound, the reactive metal will replace the less reactive metal.
  • This is beacuse the more reactive metal, bonds more strongly to the non-metal bit of the compund and pushes out the less reactive metal.
  • For example.

Copper sulfate + iron --> iron sulfate + copper

  • If a piece of silver metal is put into a solution nothing happens. the more reactive metal, copper, is already in the solution.
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Copper-rich ores

  • The supply of copper-rich ores is limited, so its important to recycle as much copper as possible.
  • The demand for copper is growing and this may lead to shortages in the future.
  • Examples of new methods to extract copper are:

- Bioleaching; Bacteria are used to seperate copper from copper sulfide. The bacteria get energy from the bond between copper and sulfur, seperating out the copper from the ore.

- Phytomining; Growing plants in soil that contains copper. the plants can't use or get rid of the copper so it gradually builds up in the leaves. The plants are burned in a furnace and the copper in collected from the ash.

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Impacts of extracting metals

  • Mining metal ores is good because it produces jobs and brings money into the area.This means services like healthcare and transport can be improved. Also useful products can be made from the metal ore.
  • However mining is bad for the environment because it creates noise , scarring of the landscape and destruction of habbitats. Also deep mine shafts can be dangerous for a long time after a mine has been abandoned.
  • Recycling metal is imporatnt because the energy used to extract metal comes from fossil fuels and these are running out. Also it uses less energy to recycle than to extract more ore.
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Properties of metals

  • Metals are strong, maluable, and conductors.
  • A metals exact properties decide how its best used.

- Copper is a good conductor, so it is used in electrical wiring.

- Aluminium is corrosion-resistant and has a low density, so it is used to make hard strong alloys, such as the metal used to make planes.

- Titanium is a low density strong metal, so it is used in hip replacements.

  • If metals are not prtected some may corrode. If a metal corrodes they lose their strength and hardness.
  • If a metal is put under a lot of stresses and strains over time it can suffer from metal fatigue. This can lead to metal breaking which can be dangerous in objects such as planes.
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Alloys

  • pure iron has a regular arrangement of identical atoms, this makes it easily shaped and bendy.
  • Most iron is converted into steel, which is an alloy.

- Bronze = copper + tin

- Cupronickel = copper +nickel

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Fractional distillation

  • Crude oil is a mixture of hydrocarbons
  • there are no chamical bonds between the different parts of the mixture.
  • This means they all keep their original properties, and can be seperated out by physical methods.
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Properties and uses of crude oil

  • All the fractions of crude oil are hydrocarbons called alkanes. these are made up of chains of carbon atoms surrounded by hydrogen atoms. the first four are: Methane, Ethane, Propane, Butane.
  • The shorter the molecules the less viscous
  • The shorter the molecules, the more volatile e.g. lower boiling point.
  • The shorter the molecules the more flammable.
  • Hydrocarbons can used for botteled gas if they are very volatile.
  • they can be used for covering roads, tar, if they are very viscous.
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Crude oil as a fuel

  • used as

- Petrol

- power stations

- central heating

  • alterantives include: wind, solar, ehtanol
  • Crude oil is limited and will eventually run out
  • crude oil is dangerous to the environment
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Environment problems

  • burning fossil fuels releases gasses such as carbondioxide into the atmosphere
  • when sulfur dioxide mixes with clouds it forms dilute sulfuric acid. this causes acid rain.
  • acid rain can be reduced by reducing sulfur emmissions.
  • increses in carbon dioxide causes climate change.
  • a bulid up of particles in the atmosphere cause global diming.
  • Ethanol pros- ca\rbon neutral. cons- convet engines
  • biodiesel: pros - less sulfur dioxide. cons - incrase in food prices.
  • Hydrogen gas: pros - combines with oxygen in the air so very clean. cons - not widly avavilable.
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