chemistry

• If there's no number after a symbol there's an invisible one there
• Balancing chemical equations

  1. Start balancing atoms that are only in compounds

  2. Can't change small numbers as that would change the compound

  3. Put numbers in front of elements or compounds to multiply them up

  4. Finish balancing elements that are not in compounds
• Mixture


  Any combination of any different types of elements and compounds that aren't chemically bonded together
• Solution


  A mixture of a solute dissolved in a solvent
• Separating mixtures

  1. Filtration for large insoluble particles

  2. Crystallization to leave solute behind after evaporating solvent

  3. Distillation to separate liquids with different boiling points
• Physical changes

  • No new substances are being made
  • Breaking intermolecular forces, not chemical bonds
• States of matter

  • Solid - particles vibrate in fixed positions
  • Liquid - particles can move past each other
  • Gas - particles move randomly and have high energy
• Gases can be compressed, solids and liquids cannot
• To melt or evaporate a substance, energy must be supplied to overcome intermolecular forces
• Atom models

  • Plum pudding model - positive charge with electrons dotted around
  • Nuclear model - positive nucleus with electrons orbiting relatively far away
• Atomic structure

  • Protons - positive charge, mass of 1
  • Neutrons - no charge, mass of 1
  • Electrons - negative charge, very small mass
• Periodic table

  • Atomic number - number of protons
  • Mass number - number of protons and neutrons
  • Isotopes - atoms of the same element with different numbers of neutrons
• Rate of reaction

  How quickly a reaction happens
• Periodic table was developed by grouping elements based on their properties, not just atomic weight
• Mean rate


  The rate could be changing over the time you measure, but this is true for any measurement over time
• Electron configuration


  Electrons fill up shells around the nucleus, with a maximum of 2, 8, 8, 2 electrons per shell
• Experiment to measure rate of reaction

  1. Reacting hydrochloric acid and sodium thiosulfate in a conical flask

  2. Measuring the volume of gas produced using a gas syringe
• Periodic table sections

  • Metals - to the left of the staircase
  • Non-metals - to the right of the staircase
  • Transition metals - in the middle
• Graph of quantity vs time

  • Curve that starts off steeply but then levels out or plateaus, showing the reaction has completed
• Group

  Column in the periodic table, indicates number of electrons in outer shell
• Tangent on graph


  Used to find the rate at any time
• Group properties

  • Group 1 (alkali metals) - lose 1 electron
  • Group 2 - lose 2 electrons
  • Group 7 (halogens) - gain 1 electron
  • Group 6 - gain 2 electrons
  • Group 0 (noble gases) - very unreactive
• Ways to increase rate of reaction

  • Increasing concentration of reactants
  • Increasing pressure of gas reactants
  • Increasing surface area of solid reactants
  • Increasing temperature
  • Adding a catalyst
• Ion


  Atom that has gained or lost electrons, no longer electrically neutral
• Reversible reaction


  Reaction where products can return to reactants
• Ionic bonding


  Metal atoms donate electrons to non-metal atoms to form a lattice of positive and negative ions
• Equilibrium


  When the rates of the forward and reverse reactions are equal, so there is no overall change
• Covalent bonding

  Non-metal atoms share electrons to fill their outer shells
• Increasing pressure


  Favours the forward reaction
• Molecular ions


  Ions formed from a group of atoms, e.g. OH-
• Increasing temperature

  Favours the endothermic (reverse) reaction
• Ionic compounds


  Consist of a lattice of positive and negative ions, have high melting/boiling points, can conduct electricity when molten or in solution
• In a reversible reaction, if the forward reaction is exothermic, the reverse reaction must be endothermic, and vice versa
• Crude oil is the result of plankton being buried under water a long time ago
• Molecular compounds


  Individual molecules held together by weak intermolecular forces, have relatively low melting/boiling points, cannot conduct electricity
• Alkanes


  Hydrocarbons with single covalent bonds, general formula CnH2n+2
• Giant covalent structures


  Atoms form an extended network of covalent bonds, e.g. diamond and graphite
• Alkane names

  • Methane (1 carbon)
  • Ethane (2 carbons)
  • Propane (3 carbons)
  • Butane (4 carbons)
  • Pentane (5 carbons)
  • Hexane (6 carbons)
• Nanoparticles are between 100-2500 nm in size, have a high surface area to volume ratio
• Fractional distillation of crude oil

  1. Heating to evaporate, then condensing at different heights based on boiling points

  2. Collecting different fractions like LPG, petrol, kerosene, diesel, heavy fuel oil