Chemistry

• Vector quantity

  Has a magnitude (size)

  Has a direction
• Limitations of the particle model


  Shows particles as spherical

  Shows particles as solid

  Forces between particles is not shown
• Allotrope


  The property of an element to exist in more than one form

  Allotropes of carbon are diamond and graphite
• Graphene

  Consists of a single layer that resembles graphite where each carbon atom covalently bonds with 3 other carbon atoms

  This allows it to be a superb conductor of electricity and it can act as a perfect barrier so that not even helium can pass through it

  It is immensely tough but ultra-light

  200 times stronger than steel but very flexible

  The thinnest material possible and transparent
• Explain why diamond is unable to conduct electricity

  Each carbon atom has four electrons in its outer shell

  In diamond, all four of these electrons form covalent bonds with four

  other carbon atoms.

  This means that all of the electrons are involved in the bonding and

  there are no delocalised electrons

  As a result, these electrons are not free to carry charge through the

  structure and so diamond cannot conduct electricity
• Nanotube

  Carbon atoms all arranged in hexagons

  Resembles a sheet of graphene rolled into a tube
• Advantages of recycling metal

  Fewer quarries and mines are needed

  Less noise, dust and heavy traffic are produced

  Smaller areas of natural habitats are damaged

  Metal ores are conserved so will last longer

  Less energy is usually needed to produce a metal by recycling than is needed to produce it from an ore.
• Disadvantages of recycling metal 


  The collection and transport of used items needs organisation, workers,

  vehicles and fuel.

  It can be difficult to sort different metals from one another.

  The sorted metal may need to be transported to where it can be turned

  into ingots.
• Polymer disposal


  Landfill

  Incineration

  Recycling
• Life Cycle Assessment

  Stage 1 - Acquisition of raw materials

  Stage 2 - Manufacturing/processing

  Stage 3 - Use and reuse

  Stage 4 - Distributions and transportation

  Stage 5 - Recycling

  Stage 6 - Disposal
• Iron is extracted from iron oxide ores by heating with

  carbon.

  Carbon displaces iron because carbon is higher in the reactivity series.

  Carbon is oxidised to form carbon dioxide, while iron oxide is reduced to iron.
• Copper is extracted from copper sulphate solution by electrolysis. Copper is deposited on the cathode as pure metal.

  Oxygen gas is formed at the anode.
• Aluminium is extracted from bauxite using electrolysis.

  The process involves dissolving alumina in molten cryolite at high temperatures.

  Aluminium is then deposited on the cathode as pure metal.

  Oxygen gas is formed at the anode.
• Metals that are high in the reactivity series will corrode easier than those lower down in the reactivity series
• Sacrificial Protection

  If two metals are in contact with one another then only the more reactive one will corrode.

  • Zinc can be attached to iron ships. Zinc is more reactive, so it corrodes before the iron does. The zinc is then replaced.
• Factors that affect absorption and emission rates


  Surface area

  Internal temperature

  External temperature
• Properties of materials

  Flexibility

  Electrical conductivity

  Tensile strength

  Thermal conductivity

  Hardness
• Tensile strength is how much a substance can be stretched
• Fullerenes 


  Molecules of carbon atoms that have hollow shapes

  Structure is mainly based on hexagonal rings of carbon atoms, but can also contain pentagonal and heptagonal rings
• Spherical fullerenes 


  Buckminsterfullerene was the first to be discovered and has the formula C60

  Spherical fullerenes can be used for catalysts, lubricants and delivering drugs into the body
• Cylindrical fullerenes 


  Carbon nanotubes are an example of this

  Due to the covalent bonds they are very strong for their size

  Cylindrical fullerenes can be used in electronics, nanotechnology and strengthening materials
• If there is a physical change of a substance this means that no new substance is made
• If there is a chemical change this means that a new substance is made and it is not easily reversible
• Changes in heat accompany the following changes

  Salts dissolving in water

  Neutralisation reactions

  Displacement reactions

  Precipitation reactions

  When these reactions take place in solution, temperature changes in the surroundings can be measured
• Endothermic reactions


  Takes in energy from surroundings and 'gets colder'

  Examples of this are thermal decomposition and sports injury packs
• When bonds break it is endothermic

  When bonds make it is exothermic
• Ionic chemical bonds 


  Involves transfer of electrons in the outer shell

  Particles are oppositely charged ions

  Occurs between metals and non-metals
• Covalent chemical bonds 


  Particles are atoms which share pairs of electrons

  Occurs in most non-metallic elements

  Happens between non-metals and non-metals
• Metallic chemical bonds


  Particles are atoms which share delocalised electrons

  Occurs in metallic elements and alloys