Chemistry

• Element


  A substance that cannot be broken down into anything simpler by a chemical reaction. Elements are made up of atoms that are all the same.
• Chemical reaction


  Atoms are rearranged during a chemical reaction. None are created or destroyed.
• Chemical change


  A new substance is made. It is irreversible.
• 5 signs of a chemical change

  • Colour Change
  • Formation of a precipitate
  • Gas formation
  • Temperature change
  • Sound production
• Writing formulae


  1. Find the ions in the ions table

  2. Circle 'floating' numbers

  3. Draw arrows

  4. Re-write anything not circled

  5. Swap and drop numbers (plus and minus cancel out)

  
• Evaporation


  Separating a soluble solid from a liquid (a soluble substance does dissolve, to form a solution)
• Chromatography


  Separating different components of a mixture by calculating the Rf value
• Distillation


  Separating water and miscible liquids due to different boiling points
• Chromatography procedure


  1. Draw a horizontal line 1.5cm above the bottom edge of the paper

  2. Place a small drop of black ink on the middle of your pencil line

  3. Pour a small volume of water into the beaker

  4. Place the bottom edge of your chromatography paper into the water

  5. Remove the paper, mark the height of the solvent front and the different coloured inks
• Atomic number


  The number of protons in the atom
• Mass number


  The total number of particles in the nucleus
• Relative atomic mass (Ar)


  The weighted average of the masses of all of the isotopes of an element
• Ion


  A charged particle with different numbers of protons and electrons
• Positive ion


  Has more protons (+) than electrons (-). Formed when an atom loses electrons.
• Negative ion


  Has more electrons (-) than protons (+). Formed when an atom gains electrons.
• Electron shell


  Electrons orbit the nucleus of an atom in shells. Shells are filled from the inside shell outwards. Electrons cannot fill a new shell until the current one is full.
• Electron configuration


  The number of electrons in each shell
• Outer shell


  The outermost electron shell (last to be filled)
• Group


  The number of electrons in the outer shell
• Period


  The number of shells containing electrons
• Atomic number


  The total number of electrons in all shells
• Group 1 metals

  All have 1 electron in their outer shell
• Group 1 metals


  • They get more reactive as you go down the group
  • Stored in oil to prevent contact with air (oxygen) and water
• Reaction with oxygen


  The metals tarnish when they react with oxygen, forming the metal oxide
• Reaction with water


  The metals react with water, forming the metal hydroxide and hydrogen gas
• Properties of Group 1 metals


  • Float
  • Fizz
  • Move
  • Melt
  • Burn
• Group 7 halogens


  All have 7 electrons in their outer shell
• Group 7 halogens


  • They get less reactive as you go down the group
  • Non-Metallic properties – poor conductors, low melting/boiling points, low density
  • Diatomic molecules – F2, Cl2, Br2
• Reaction of halogens and iron wool

  Halogens react with iron wool to form iron halides. The speed of which indicates reactivity.
• Halide ion solutions


  • Potassium chloride
  • Potassium bromide
  • Potassium iodide
• Flame tests


  Used to identify metal ions
• Silver nitrate test


  Used to test for chloride, bromide or iodide ions
• Group 0 noble gases

  All have full outer shells, making them unreactive (inert)
• Group 0 noble gases

  • Unreactive & low density
  • Emit light when electricity passes through
  • Used in party balloons, weather balloons, advertising signs, inert atmosphere for welding & in lightbulbs
• Calculating Mr


  Find the mass numbers of each element and add them up
• Calculating percentage mass


  Divide the mass of the element by the total Mr and multiply by 100
• Percentage yield


  Compares the predicted yield (what we should get) with the actual yield (what we actually get in practice)
• Calculating percentage yield


  Percentage yield = (actual yield / theoretical yield) x 100
• Simplest formula (higher only)

  Find the mass difference, divide by the Ar, and find the ratio
• Mole


  A term that describes a specific number - 6.02 x 10^23 atoms