Chemistry A3

• solid

  • has strong forces of attraction
  • a fixed position
  • a regular lattice arrangement
  • definite shape/volume
  • vibrates
• liquid

  • has some force of attraction
  • doesnt keep a definite shape
  • keeps the same volume
  • is free to move (randomly)
• gas

  • has no force of attraction
  • is free to move (randomly)
  • doesnt keep a definite shape/volume
  • travels in a straight line.
• The particle model isnt perfect because it doesn't show the size of particles, space between them or forces (and their strength)
• Physical change


  Reversible, no new substance made
• Chemical change


  Not reversible, forms new product
• John Dalton's atomic model


  • Atoms are solid spheres
• Rutherford's gold foil experiment

  • Discovered the nucleus, 90% of particles deflected
• Bohr's model

  • Electrons can only exist in fixed orbits/shells, each shell has a fixed energy
• Peer-review


  Other scientists find errors and develop their own work
• Subatomic particles

  • Protons (mass 1, charge +1)
  • Neutrons (mass 1, charge 0)
  • Electrons (mass 1/2000, charge -1)
• Mass number

  Total number of protons and neutrons
• Atomic number


  Number of protons/electrons
• Isotopes

  Different forms of the same element with the same number of protons but different number of neutrons
• Mendeleev's periodic table

  • Arranged elements by atomic mass, similar properties in same vertical groups, left gaps for predicted elements
• Modern periodic table


  • Arranged by similar chemical properties = same group
• Electron shell rules

  • Lowest energy shells filled first
  • 1st shell 2 electrons
  • 2nd shell 8 electrons
  • 3rd shell 8 electrons
• Metallic bonding


  Electrostatic attraction between metal ions and free-moving electrons
• Ionic bonding


  Oppositely charged ions strongly attracted by electrostatic forces
• Covalent bonding

  Atoms share pairs of electrons
• Substances with covalent bonding

  • Diamond
  • Graphite
  • Fullerenes
• Polymerisation

  Joining of monomers, needs high pressure and a catalyst
• Ionic compounds

  High melting/boiling points, don't conduct electricity, usually dissolve in water
• Metallic bonding

  Electrostatic attraction between metal ions and free-moving electrons, high melting/boiling points, strong, bendable, malleable, good conductors, react with oxygen
• Chromatography

  • Mobile phase where molecules can move (liquid or gas)
  • stationary phase where molecules can't move (solid or viscous liquid)
• Rf value

  Distance travelled by solute / distance travelled by solvent
• Gas chromatography

  • Mobile phase is unreactive gas
  • Stationary phase is viscous liquid
  • Used to analyse unknown substances
• Purity

  • Pure substances has specific melting and boiling point
  • A mixture has a range
• Relative atomic mass

  Average mass of one atom compared to 1/12 mass of carbon-12 atom
• Molecular formula

  Shows number of atoms of each element
• Empirical formula

  Simplest ratio of atoms
• In a chemical reaction, mass is always conserved unless a gas escapes
• Half equation

  Uses e- to show one electron
• Mole

  One mole of an atom or molecule of any substance will have a mass in grams equal to the relative formula mass for that substance
• Number of moles


  Mass in g (of element) / Mr (of element)
• Concentration


  Measure of how crowded things are
• Exothermic


  Gives out energy, surrounding temperature rises
• Endothermic


  Takes in energy, surrounding temperature decreases
• Activation energy

  Minimum amount of energy needed for bonds to break and a reaction to start
• Bond breaking

  Endothermic process