Chemistry C2

• They have single covalent bonds
• They are saturated hydrocarbons as they have no spare bonds
• They don't decolourise bromine water because there are no spare bonds
• They don't form polymers because there are no spare bonds

• They have one or more double covalent bond
• They are unsaturated hydrocarbons because they have spare bonds left
• They decolourise bromine water because they form bonds with the bromine atoms
• They form polymers as their double bonds open up to form a long chain
• Alkenes react with water to make alcohol

Long chain hydrocarbons form thick liquids which aren't useful. Cracking is used to split the hydrocarbons to make much shorter molecules which are more useful. Cracking is just heating up the molecules to break them down. Cracking produces alkenes which are needed to make plastics. In the industry, cracking occurs when vaporised hydrocarbons are passed over a powdered catalyst at between 400 and 700C. Silicon dioxide and aluminium oxide are both catalysts. 

Plastics are long chain molecules called polymers.  There are two types of polymers, thermoplastic and thermosetting. The thermoplastic polymers (e.g polythene) have weak bonds, so can be melted and remoulded easily. The thermosetting polymers have crosslinks between chains so have a much more rigid and solid structure. The polymer doesn't soften when it's heated but it does burn. Plasticisers are added to plastic, they get between the chains and allow them to move around more freely, this is what makes plastic more flexible.

Ar - the relative atomic mass of one element is usually the same as the mass number. If an element has more than one stable isotope then the average mass of all the isotopes is the Ar. 

If there is a compound then the relative formula mass (Mr) is used, which is all the relative atomic masses added together. e.g. MgCl2 = 24 + (35.5x2) = 95. 

In the first shell 2 electrons are allowed, in the second 8 and in the third 8. If the outer shell is not full then this is why the atoms react. 

The electron configuration is the number of electrons in each shell. The periodic table shows the number of protons the element has. Lithium has three protons. Therefore Lithium has 3 electrons. Because the maximum number of electrons in the first shell is 2, the electron configuration is 2,1. 

• Metals have a giant structure
• They have free electrons which come from the outer shell of every atom in the structure
• They are good conductors of heat and electricity
• They are malleable
• They have high melting and boiling points
• Some transition metals are hard
• Alkali metals are quite soft (more malleable)
• Metals can be mixed together to make alloys
• Alloys make metal harder

• More collisions between particles increase the rate of reaction
• higher temperature increases collisions as the particles move faster - which means they will hit each other more
• Higher concentration increases collisions - if the solution has more particles knocking about between water molecules
• Increasing the pressure means the particles are more squashed up
• larger surface area - more useful collisions
• Catalysts increase number of successful collisions by giving the reacting particles a surface to stick to. They lower the activation energy