chemistry

• in solids there are strong forces of attraction between particles, which hold close together in fixed positions to from a very regular lattice arrangement
• if a temperature is below the melting point of a substance, it'll be a solid. if it's above the boiling point it'll be a gas. if it's between the two points, then it's a liquid
• Na = sodium

  Fe = iron

  Pb = lead
• CH4 = one carbon atom, four hydrogen atoms

  
• • water - H2O
  • Ammonia - NH3
  • carbon dioxide - CO2
  • hydrogen - H2
  • chlorine - Cl2
  • oxygen - O2
  • ( hydrogen,chlorine, and oxygen are all diatomic as they contain two atoms)
• ionic compounds form giant lattices instead of individual molecules.
• the formula of an ionic compound tells you the ratio of elements in the compound. E.g sodium chloride, NaCl has one chlorine atom for every one sodium atom
• an exothermic reaction is one which gives out energy to the surroundings. this is usually shown by a rise in temperature of the surroundings
• metals consist of giant structure
• the bonding in metals can be described by a model. This states that the electrons in the outer shell of the metal atoms are delocalised (delocalised) there are strong forces of electrostatic attraction between the positive metal ions and the 'sea' of shared negative electrons.
• these forces of attraction hold the atoms close together in a regular structure and are known as metallic bonding. metallic bonding is very strong.
• compounds that are held together by metallic bonding include metallic elements and alloys
• metallic bonding determines the properties of metals
• metals have a set of bulk of properties which can be explained by their metallic bonding
• the electrostatic forces between the metal ions and the sea of delocalised electrons are very strong, so need lots energy to be broken. This means that most substances with metallic bonds have very high melting and boiling points, so they're generally solid at room temp
• the delocalised electrons are free to move so can carry electrical current and thermal(heat) energy through the material, so metals are good conductors of electricity and heat
• the layers of atoms in a metal can slide over each other whilst still being held together by electrons, making metals malleable and ductile - this means that they can be bent, hammered or rolled into flat sheets and drawn into wires
• 1. metal atoms react, they form positive ions by losing one or more electrons. This means they can form ionic compounds.
  2. for metals, their reactivity is determined by how easily they lose electrons. The higher up the reactivity series a metal is, the more easily it loses electrons and forms positive ions.
  3. you can deduce the order of reactivity of different metals by looking at their reactions with water, acid or other metals compounds.

  
• fractional distillation can be used to separate hydrocarbon fractions
• crude oil is a mixture of lots of different hydrocarbons, most of which are alkanes.
• the different compounds in crude oil are separated by fractional distillation
• fractional distillation:

  the oil is heated until most of it has turned into gas. the gases enter a fractional column (and the liquid bit is drained off)

  the fractionating column is a tall column which has condensers coming off at various points.

  the column is heated from the bottom so there's a temperature gradient (hot at the bottom, gets cooler as you go up)

  the longer hydrocarbons have high boiling points. They condense back into liquids and drain out of the column early on, when they're near the bottom. The shorter hydrocarbons have lower boiling points.
• there are two types of bonds in crude oil: strong covalent bonds between the atoms with hydrocarbon molecules and weaker inter molecular forces of attraction between hydrocarbons molecules to the mixture
• crude oil is used for petrol, kerosene, diesel oil and heavy fuel oil
• fractional distillation can also separate crude oil in the lab
• Crude oil substitute fractionation

  1. Put crude oil substitute in a flask

  2. Attach a fractionating column and condenser above the flask

  3. Gradually heat the flask

  4. Liquids with lowest boiling points evaporate first

  5. Collect this fraction in a collection vessel

  6. Liquids with higher boiling points condense and run back down

  7. When temp reaches 50 degrees, replace collection vessel

  8. Collect further fractions, changing vessel each time temp raised by 50 degrees
• cracking means splitting up long chain hydrocarbons
• at the cathode: Al3+ + 3e- = Al

  aluminium is produced at the cathode.

  reduction - a gain of electrons
• at the anode: 2O2- = O2 + 4e-

  oxygen is produced at the anode.

  oxidation is the loss of electrons
• aluminium oxide = aluminium + oxygen

  2Al2O3(l) = 4Al(l) + 3O2(g)
• fluorine = pale yellow gas
• chlorine = poisonous green gas
• bromine = poisonous red-brown liquid which gives off orange vapour when heated
• iodine = dark grey crystalline solid that gives off purple vapour when heated