Y9 Chemistry End Of Year

• Group names


  Group 1: The Alkali Metals

  Group 2: The Alkaline Earth metals

  Group 3 - 6: Transition metals

  Group 7: The Halogens (most are poisonous)

  Group 8/0: The Noble Gases
• Reactivity series


  Potassium - most reactive

  Sodium

  Calcium

  Magnesium

  Aluminium

  Carbon - not a metal

  Zinc

  Iron

  Tin

  Lead

  Hydrogen - not a metal

  Copper

  Silver

  Gold

  Platinum - very unreactive
• Element


  A substance made up of only one type of atom
• Compound


  a substance containing two or more different elements chemically bonded together
• Molecule


  Two or more non-metal atoms chemically combine to form molecules
• Mixture


  Two or more different substances mixed together but not chemically bonded
• Democritus


  400 BC

  Proposed that all matter is made of indestructible particles be called atoms

  
• John Dalton


  1803

  Said that elements consist of identical atoms and different elements combine to make compounds

  
• JJ Thomson


  1898

  Discovered the electron and developed the plum-pudding model of the atom

  
• Ernest Rutherford


  1919

  Demonstrated the existence of the atomic nucleus and discovered the proton

  
• Rutherford’s Gold Foil Experiment

  → fired positive particles at gold foil → Most (~ 99%) went straight through the foil sheet - atoms are mostly empty space → Small number were deflected by large angles - small positive charge of nucleus

  -> 1 in 10,000 bounced back towards him - the nucleus is about 1/10,000 of the size of an atom

  
• Niels Bohr


  1922

  Proposed the outer shell held more electrons than the inner shell

  
• James Chadwick


  1932

  Discovered neutrons

  
• Structure of the atom

  Protons & neutrons - in the nucleus (same size) - 1

  electrons - outside (smallest) - 1/1840
• Atoms represented in the periodic table

  mass number ( number of protons & neutrons )

  A

  X - element

  z

  atomic number ( number of protons )
• Ions


  A charged atom - can only be formed by adding or subtracting electrons.

  e.g Fe +2, I- end of the ion changes into -ide e.g iodide ion etc
• Isotopes


  Atoms of the same elements ( the same number of protons ) but different number of neutrons (different mass numbers)

  hydrogen has 3 isotopes:

  
• Relative atomic mass


  average mass of element taking into account the abundance of all isotopes
• RAM equation


  RAM = Sum of (mass x abundance)/

  Total abundance

  e.g RAM of Cl = (35x75%) + (37x25%)/

  75+25

  = 35.5
• Electronic Structures


  2,8,8 - repeat

  the group the element is in is the amount of atoms in its outer shell
• Why do elements from different ions?

  When elements react, they try to gain or lose electrons to get a FULL OUTER SHELL.

  metals LOSE electrons —> form +ive ions

  non-metals GAIN electrons —> form

  -ive ions

  IONS ALWAYS HAVE FULL OUTER SHELLS
• Group 1

  Alkaline metals

  Group 1 are +1 ions - meaning they lose one electron

  react vigorously with water.

  get more reactive the further down the table.

  only form +1 ions

  Lithium:

  • burns with red flame
  • residue lithium oxide

  Sodium:

  • burns with orange/yellow flame
  • residue sodium oxide

  Potassium:

  • Burns with purple flame
  • residue potassium oxide
• Why do alkali metals have to be stored in oil?


  so they don’t react with the moisture in the air
• Group 0

  Noble Gases Don’t react bc they already have a FULL OUTER SHELL
• Group 7

  • Non metals
  • 7 in outer shell
  • all are diatomic molecules - contain two atoms
  • as you go down the group, the melting point and boiling point increases, the mass of the elements also increase.
  • only form -1 ions.
  • the halogens
• more shells, the harder to gain and easier to lose


  the magnetic pull makes it harder to lose so the more the shells the better
• Hydrogen 


  gas at room temperature

  lighter than air

  much more reactive than helium

  low density

  behaves like a non metal
• Argon


  The most abundant noble gas

  used lots as it’s unreactive
• Transition metals

  • absorb visible light which is why we see them as colourful
  • useful as catalysts - lower activation energy.
  • strong and hard
  • high melting points
  • easy to cut through
• Rate of reaction


  The rate of reaction is a measure of how quickly a REACTANT is used up, or a PRODUCT is formed
• Rate of reaction equation


  Mean rate of reaction = Quantity of reactant used / time taken

  OR

  Quantity of product formed/time taken
• Reaction rate - time graph

  The gradient of the line is equal to the rate of reaction

  Fast reactions - seen when the line becomes horizontal
• Tangent 


  A straight line that touches a single point on a curve

  
• When the rate begins to gradually decrease…


  This means that there’s less reactant present as it is running out meaning less product can be formed
• For two atoms to react…

  they must collide with enough energy for them to stick together
• Activation Energy


  The minimum amount of energy that colliding particles require to react
• Four factors determine the rate of reaction

  • concentration (of a solution)/pressure(of a gas)
  • Surface area (of a solid)
  • Temperature
  • Presence of a catalyst
• Increasing Concentration

  • the higher the concentration, the closer the particles and the more FREQUENT the SUCCESSFUL collisions
• Increasing Temperature

  • particles have more energy (heat makes them vibrate)
  • more particles have enough energy needed for reacted - more than the activation energy
  • also move faster - more frequent, successful collisions
• Increasing Surface Area

  • the bigger the surface area to volume ratio (the smaller you break something into, the more surfaces you are creating)
  • more frequent, successful collisions