Chemistry

Atom:

• Proton  - Nucleus (+1)
• Neutron - Nucleus (0)
• Electron - Shells (-1)

Atoms: Neutral because no. of Protons = no. of Electrons

Atomic Mass: No. of Protons

Mass Number: No. of Protons + Neutrons

Isotopes: Atoms of the same element with a different mass number

Element: Pure substance made up of only 1 atom

Compound: Pure substance made up of 2 or more different atoms chemically joined together

Orbitals:

• Electrons exist in shells around the nucleus
  • 1st - 2 electrons
  • 2nd - 8 electrons
  • 3rd - 8 electrons

Ion:

• Electrically charged atom
  • Losing electron = positively charged
  • Gaining electron  = negatively charged

Ionic bond: Metal + non-metal = Electrons move from metal to non-metal and the attraction between the postitive and negative charges form an ionic bond

Dot + Cross diagrams:

Properties:

• Electrical Conduction:
  • Solid = no conduction because ions cannot move
  • Molten = conduction because ions are free to move
• Structure:
  • Ions arranged in giant ionic lattice - postive + negative electrons held together by strong electrostatic attraction
• Melting Point:
  • Very high - lot of energy is required to overcome the electrostatic attraction
  • MgO is higher than NaCl because MgO has doubly charged ions, this means there is a stronger attraction between ions

The Period Table:

Covalent bond:

• Non-metal + non-metal:
  • Electrons are shared between atoms
  • Form molecules and giant covalent networks

Molecular Structures:

• Do not conduct electricity - no ions, so electrons cannot move
• Low Melting Point and Boiling Point - weak intermolecular forces between molecules

Alkali Metals:

• Go down the group = more reactive
  • Further away the outer shell electron is from the nucleus means that it gets lost more easily
• When put in water (OIL):
  • Lithium -  Fizzes slowly, floats, disappears slowly, remains cube
  • Sodium -  Fizzes quickly, floats, disappears quickly, forms a ball, catches fire (yellow flame)
  • Potassium - Fizzes violently, floats, disappears very quickly, forms a ball, catches fire (lilac flame)
• alkali metal + water → metal hydroxide + hydrogen gas
  •  
    •  
      • 2M + 2H₂O → 2MOH + H₂
• Density -  Increases as you go down
• Melting point -  Decreases as you go down

Fireworks:

• Contain metal compounds that vapourise in high temperatures
• The electrons absorb heat energy and jump into a higher shell, then they drop back into their normal shell when light energy is produced

Flame Tests:

• Different metal ions = different colours
  • A loop of nichrome wire is cleaned (dip in HCl, then place under blue flame of bunsen, till the colour doesnt change)
  • Loop is dipped into acid to moisten it, then into the solid sample
  • Loop is then held over the edge of the blue flame and the colour observed
• Lithium   -Red
• Sodium -Orange
• Potassium -Lilac

Halogens:

• React with metals to form salts
  • Chlorine - Green gas
  • Bromine  - Orange liquid
  • Iodine  - Grey solid (purple gas when heated)
• Melting point and Boiling point increase as you go down the group
• Metal + Halogen → Metal Halide
  •  
    • 2M + X₂ → 2MX

Go down the group = reactivity decreases 

• Chlorine - displaces bromine + iodine
• Bromine - displaces iodine
• Iodine - no displacement

• You can tell there is a reaction because the colour changes (halogens = coloured, halide = colourless)
  • X₂ + 2MY → Y₂ + 2MX
    • Cl₂ + 2NaBr → Br₂ + 2NaCl
    • Chlorine + Sodium Bromide → Bromine + Sodium Chloride

Similar Properties (RIG):

• Gain an electron and become negatively charged
• Stable electronic structure

Fluorine is more reactive because electrons are negative, so they are attracted to the positive nucleus, and the further away from the nucleus means that the attraction decreases too.

Properties:

• Strong
• Shiny
• Malleable
• Pretty colours:
  • Copper compounds = Blue
  • Iron (II) compounds = Light Green
  • Iron (III) compounds = Orange/Brown

Catalysts:

• Haber Process  -Iron
• Hydrogenation -Nickel
• Contact Process -Vanadium Pentoxide

Thermal Decomposition (heated and broken down to form 2+ substances):

• Metal Carbonate → Metal Oxide + Carbon Dioxide

When a mixture of solutions react together to form an insoluble solid, called a precipitate and it makes the mixture cloudy.

Hydroxide Precipitates:

• Transition element is dissolved in water, so the metal ions separate out and react with the hydroxide ions to form a coloured metal hydroxide precipitate
  • Copper (II)  = Blue
  • Iron (II) = Light Green
  • Iron (III)  = Orange/Brown

•  
  •  
    • Cu²⁺ + 2OH^- à Cu(OH)₂

Metals are held together by metallic bonding:

• Positive metal ions are held together by a 'sea' of delocalised electrons, so they are free to move
• Strong attraction between positive metal ions and negative electrons

Properties of Metals:

• High Melting + Boiling Points
  • there are strong forces of attraction between the sea of delocalised electrons and positive metal ions, therefore lots of energy is needed to overcome this
• Good conductors
  • because the delocalised electrons are free to move past the metal cations
• High Tensile strength
  • strong forces of attraction mean they resist being stretched

The resistance of metal decreases as the temperature decreases, which is why some metals become superconductors at low temperatures

• Superconductor = material with little/no resistance to the flow of electricity
  • Uses:
    • Powerful electromagnets (MRI)
    • Superfast electronic circuits
    • Transmit power with minimum energy loss
  • Drawbacks:
    • Only work at very low temperatures (-273), so application is limited
    • Scientists trying to develop some that work at 20C

Places to get water:

• Aquifers, Reservoirs, Lakes and Rivers

Uses of Water in Industry:

• Coolant, Solvent and Cheap raw material

Pollutants:

• Nitrates from fertiliser, Lead from old pipes, Mineral salts and Pesticides from crops

Purifying Water:

• Sedimentation - Removes large particles (chemicals added causing them to clump together and fall to the bottom)
• Filtration  - Removes small suspended particles (water is passed through beds of sand and gravel to trap the little bits)
• Chlorination  - Kills microbes in the water (chlorine gas added to help prevent diease)

Use precipitate reactions to test for ions in water:

• Sulfate Ions:
  • Use barium chloride - a white precipitate forms (barium sulfate)
    • Sodium sulfate + barium chloride → barium sulfate + sodium chloride
      • Na₂SO₄ + BaCl₂ à BaSO₄ + 2NaCl
• Halide Ions:
  • Use silver nitrate:
    • Chloride  - White 
    • Bromide - Cream
    • Iodide  - Yellow
      • Sodium chloride + silver nitrate → Silver chloride + Sodium nitrate
        • NaCl + AgNO₃ à AgCl + NaNO₃