Elements of Sea

• As you go down the Halogen Group, the abundancy (availability) of the elements decreases. The reactivity decreases as you go down the group because it’s harder to gain an electron due to increased electron repulsion and the further away the outershell is from the positive nucleus.
• Fluorine is a pale yellow gas, Chlorine is a green gas, Bromine is a dark red liquid, Iodine is a shiny black solid, all at room temperature (298K)
• As you go down the Halogen group, the darker in colour the substances get, the melting and boiling point increases, the states go from Gas to Liquid to Solid, and the elements become less volatile (how easily a substance turns into vapour)
• The strongest oxidising agents are at the top of the Halogen group. The stronger oxidising agents displace the weaker oxidising agents in a displacement/ redox reaction.
• Silver + Chlorine = Silver Chloride, a white precipitate. Silver + Bromine = Silver Bromide, a cream precipitate. Silver + Iodine = Silver Iodide, a pale yellow precipitate. The reactants are always aqueous, whilst the products are always solid.
• Silver Chloride + Ammonia Solution = a colourless solution. Silver Bromide + Ammonia Solution = an off-white solution. Silver Iodide + Ammonia Solution = a pale yellow solution. This means that the solubility of silver halide ions decrease as you go down the halogen group.
• Oxidising Agents gain an electron from a chemical and is reduced in a reaction. Reducing Agents donate an electron for a chemical and is oxidised in a reaction. Oxidation is the loss of electrons and Reduction is the gain of electrons. Oxidised chemicals increase in oxidation number and Reduced chemicals decrease in oxidation number.
• For an element, the oxidation state will always be zero. For a simple ion, the oxidation state is the charge of the ion. For a compound (that has no charge), the oxidation states of the elements must add to equal zero. For a more complicated compound (a compound with charge) the oxidation states of the elements must add to the charge stated on the compound.
• Rules for Oxidation States: All halogens except oxygen has an O.S. of -1. Oxygen has an O.S. of -2, Hydrogen has an O.S. of +1. Group 1 = +1, Group 2 = +2, Group 3 = +3. This applies for elements in a compound. For a halogen halide, the stronger oxidising agent will have the O.S. of -1. Order of halogens is: F - Cl - Br - I
• When using systematic naming for compounds. the oxidation state is only mentioned when the element in question is either: a transition metal, a halogen, Sn (Tin), Pb (Lead), S (Sulfur), N (Nitrogen). The roman numeral refers to the oxidation number of the element that it appears next to.
• An Oxyanion is a negative ion that contains an oxygen, the name ends with an ‘-ate’. With oxyanions, focus on the oxidation state of the oxygen and then the other element. Examples of oxyanions, nitrate(V), chlorate(III) and sulfate(V).
• In electrolysis, the positive cations migrate to the negative cathode and the negative anions migrate to the positive anode. The element at the cathode is reduced and the element at the anode is oxidised. The product at the cathode is metal whilst the product at the anode is a non-metal. Water can be both oxidised and reduced in electrolysis.
• Halogens dissolved in water [Lower Layer]:

  • Chlorine = pale green
  • Bromine = orange
  • Iodine = brown

  Halogens dissolved in cyclohexane:

  • Chlorine = pale green
  • Bromine = orange/ brown
  • Iodine = violet
• [At Cathode] NEEDS TO BE REWORDED, SLIGHTLY INCORRECT

  When metals are more reactive than hydrogen on the reactivity series, they remain as ions in solution and hydrogen gas is produced.

  Observation = bubbling/ fizzing at cathode

  Metals that are less reactive than hydrogen will be deposited on the cathode. This includes copper, silver, gold and platinum.

  Observation = metal deposit on cathode

  
• [At Anode]

  The halide ions have a greater tendency to be oxidised, therefore a colour change in solution surrounding the anode is observed.

  Observation =

  • Chlorine: bubbles + pale green gas
  • Bromine: orange/ brown
  • Iodine: dark brown

  Any other negative ions, oxygen is produced.

  Observation = colourless gas
• A dynamic equilibirum occurs in a closed system whilst the rate of the forward and backward reaction remain equal and are happening simultaneously (hence, dynamic). The concentrations of both products and reactants remain constant NOT EQUAL.
• 1. Forward Reaction
  2. Backward Reaction
  3. Equilibrium State
  4. Time
  5. Reaction Rate

  The rate of the forward reaction decreases, therefore their concentrations will decrease until equilibrium reached. The rate of the backward reaction is zero at the start since there’d be no products immediately when the reactants are added. Soon the rate of the backward reaction increases, therefore their concentrations will increase until equilibrium reached. The equilibrium state is when both rates are constant.

  Curved line that goes straight at end = plateau