The Periodic Table

  • Created by: ernily
  • Created on: 09-04-15 18:01

Periodic Trends

  • Atomic Radius Decreases Across A Period.
  • Number of protons increases, so the positive charge of the nucleus increases.
  • Electrons are pulled closer to the nucleus, so atomic radius decreases.
  • Shielding doesn't change because the extra electrons gained are added to the outer energy level.
  • Ionisation Energy Increases Across A Period.
  • Number of protons increases, causing a stronger nuclear attraction.
  • Extra electrons are roughly the same energy level, so there is little shielding or extra distance to lessen the nuclear attraction.
  • Ionisation Energy Decreases Down A Group.
  • There are extra electron shells, so there is weaker nuclear attraction.
  • The shielding between the outer electrons and the nucleus overcomes the nucleus' positive charge.
  • Melting & Boiling Point Increase Across A Period.
  • Metals: The metallic bonds get stronger; increasing number of delocalised electrons and decreasing ionic radius. Higher charge density.
  • Macromolecular: Atoms are linked by strong covalent bonds, lots of energy needed to break the bonds.
  • Simple Molecular Substances: Van der Waals' forces are easily overcome.
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Group 2 - The Alkaline Earth Metals

  • Group 2 elements lose their outer electrons to form 2+ ions.
  • Reactivity increases down group 2. When they react, they lose electrons. The easier it is to lose electrons, the more reactive the element.
  • Group 2 elements react with water to produce hydroxides.
    • Metal Hydroxide + Hydrogen
  • They burn in oxygen to form solid, white oxides.
  • Group 2 oxides and hydroxides are bases.
  • They form alkaline solutions in water.
  • The oxides form more strongly alkaline solutions as you go down the group
  • Hydroxides become more soluble.
  • Thermal Decomposition: When a substance breaks down when heated.
  • Group 2 carbonates decompose to form the oxide and carbon dioxide.
  • Thermal stability increases down the group, so it takes more heat to decompose carbonates.
  • Group 2 compounds are used to neutralise acidity.
    • Calcium Hydroxide [Ca(OH)2] is lime; used to neutralise soils.
    • Magnesium Hydroxide [Mg(OH)2] is an antacid.
    • H+ (aq) + OH- (aq) --> H2O (l)
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Group 7 - The Halogens

  • Boiling and melting point of halogens increase down the group.
  • Due to increased strength of van der Waals forces.
  • Halogens become less reactive down the group.
  • They react by gaining an electron - they are oxidising agents.
  • Shielding increases, so attraction is lower.
  • Halogens displace less reactive halide ions.
  • F > Cl > Br > I > Al
  • Silver Nitrate Solution is used to test for halides.
  • Chlorine --> White precipitate.
  • Bromine--> Cream precipitate.
  • Iodine --> Yellow precipitate.
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Disproportionation & Water Treatment

  • Halogens undergo disproportionation with alkalis.
  • Chlorine and Sodium Hydroxide make bleach
  • 2NaOH + Cl2 --> NaClO + NaCl + H2O
  • Chlorine is used to kill bacteria in water.
  • Chlorine + water = disproportionation.
  • Cl2 + H2O --> HCl + HClO (reverisible reaction)
  • Aqueous chloric (i) acid ionises to make chlorate (i) ions.
  • Chlorate (i) ions kill bacteria.
  • Adding chlorine makes water safe to drink and swim in.
  • Benefits Of Chlorine In Water:
    • It kills disease-causing microorganisms.
    • It prevents reinfection further down the water supply.
    • It prevents growth of algae.
  • Risks Of Chlorine In Water:
    • Chlorine gas is very harmful if inhaled.
    • Chlorine reacts with organic compounds in water to form chlorinated hydrocarbons.
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