C2

Material Properties

• Melting point- temperature at which a solid turns into a liquid
• Tensile strength- the force needed to break a material when it is being stretched
• Compressive strength- force needed to crush a material when it is being squeezed
• Stiffness- the force needed to bend a material
• Hardness- how well a material stands to wear
• Density- the mass of a given volume of a material

• Metals- shiny, malleable, and electrical conductors
• Ceramics- clay, glass, and cement. hard and strong
• Polymers- large molecules used to make rubbers, plastics, and fibres

• Natural Materials- cotton and paper, from plants and silk and wool from animals
• Synthetic Materials- manufactured by chemical reactions using raw materials

• Crude oil is a mixture of thousands of hydrocarbons
• nearly 90% of crude oil is used as fuels
• around 3% of crude oil is used to synthesis other chemicals 

Fractional Distillation-

• the oil is heated up which turns it into all gases
• the distillation tower is cooler at the top
• gas molecules condense into liquids when they cool
• liquids with similar boiling points collect together, we call these fractions
• hydrocarbons in each fraction have boiling points within a range of temperatures
• molecule chain lengths are similar sizes within each fraction
• the smaller the molecule chain length, the lower the boiling point

• a polymer is a large molecule made by joining many smaller molecules called monomers
• a polymer is made by a process called polymerisation
• small forces attract molecules to eachother
• the forces are strongest when molecules are close together
• the stronger the force the more energy is needed to seperate the molecules
• low density polyethene has long molecules with branches, the branches keep molecule chains apart so the forces between different molecules are weak
• high density polyethene has long chains but no branches, so the molecules are close together and it is much stronger
• high crystalline polymers are strong with high melting points but can be brittle
• longer chains need more force to seperate them
• plasticisers are used to make polymer softer, and weaken the forces between molecules

• nanotechnology is the use and control of very small structures
• a nanometre is one millionth of a millimetre
• nanoparticles have high surface area so are more reactive
• they range in size from 1nm-100nm
• silver nanoparticles are good at killing bacteria
• titanium oxide nanoparticles are put into sunscreen 
• if silver nanoparticles are released into the environment they could kill lots of useful micro organisms
• the effects of nanoparticles are not yet known