Elements of the Sea
28 May 2024 14:46
ES1 Chemistry of Halogens
Halogens are p-block elements in group 7, they have seven electrons in the outer shells and are Reactions of halogens with halide ions:
the most reactive non-metals. They are found most naturally in compounds and the most The more reactive halogen will displace the less reactive halide and take its place.
abundant halogens are fluorine and chlorine however all of them are diatomic. They achieve These are often shown as ionic equations, where the spectator ions are removed, or
stability via ionic or covalent bonding. half equations, which show the loss/gain of electrons. These displacement reactions
are also redox reactions as both oxidation and reduction has occurred. Colour
changes can be difficult to see, adding an organic solvent makes the change more
Properties down the group:
distinct.
- Darker in colour - Gas --> Liquid --> Solid
- Melting and boiling point increases - Less volatile
Reaction of halide ions:
Reaction of halide ions with silver nitrate:
Solubility: Reactions with silver nitrate and halide ions are precipitation reactions where a solid is
There is no set trend for solubility, but all halogens are more soluble in organic solvents than formed, in this case it is a silver halide where 'X' is the halogen;
in water and this also makes them more distinguishable.
Ag+ (aq) + X- (aq) --> AgX(s)
Colours of silver halides can be hard to distinguish so ammonia solution is added as the
solubility of them in ammonia decreases down the group.
Halogen Colour of silver halide
Halogens in water (L -> R) Halogens in cyclohexane (L -> R)
Chlorine White precipitate
Chlorine - pale green Chlorine - pale green Bromine Cream precipitate
Bromine - orange/yellow Bromine - orange/brown
Iodine Yellow precipitate
Iodine - brown Iodine - violet purple
Chemical properties and reactions: Halogen Colour of silver halide + ammonia
Halogens are very reactive, they tend to remove electrons from other elements to complete their solution
own outer shell. This makes them oxidising agents (get reduced as they gain an electron) and the Chlorine Colourless
elements at the top of the group are the strongest oxidising agents. This trend in because as the Bromine Clouded/translucent yellow
size of the atom increases the further away the outer shell is and they gain electrons less readily.
Iodine (more) opaque yellow
ES2 Oxidation states and redox
Oxidation is: Element Oxidation state
Reduction is:
- Loss of electrons - Gain of electrons Fluorine -1
- Gain of oxygen - Loss of oxygen Oxygen -2 except with F or in
- Increase in oxidation state - Decrease in oxidation state
peroxide ion (O22-)
Oxidation states: Chlorine -1 except with F or O
Oxidation states are numbers assigned to an element in a chemical which tells you how many electrons have been lost or gained compared to Bromine -1 except with F, O, Cl
the unreacted chemical. Oxidation states follow several rules:
Iodine -1 except with F, O, Cl,
- Elements always have an oxidation state of 0
Br
- Ions have the same oxidation state as their charge
- Charges of compounds must equal zero overall Hydrogen +1 except in metal
hydride
Some elements have constant oxidation states which can be used to work out other oxidation state of elements in a compound Group 1 +1
Group 2 +2
Aluminium +3
Oxidation states and systematic naming:
The systematic names have Roman numerals in brackets that show the oxidation state of the part of the compound when that element may
have different oxidation states e.g. sulphuric(VI) acid shows that the sulphur in the compound has a an oxidation state of +6.
Oxyanions are negative ions with an oxygen in, they are signalled by -ate and a Roman numeral to show oxidation state.
ES3 Electrolysis
Electrolysis of molten compounds: Reduction at the cathode:
Solid ionic compounds do not conduct electricity as ions are not free to move, At the cathode, there are metal ions from the salt AND water. More reactive metals remain as ions and
once they are molten then the charged ions are able to move around and carry a
the hydrogen gas is released by the reduction of water, less reactive metals are deposited on the
current.
cathode.
Positive metal cations migrate to the negative electrode, the cathode, and negative
Oxidation at the anode:
anions migrate to the positive anode. The hot molten metal will collect at the
At the anode, there are negative ions from the salt and the water, halides are more likely to be oxidised
bottom of the container, usually it is reduced and gains electrons and any gas
than water so a halogen is produced. Other anions such as sulphates or nitrates are less likely to oxidise
products will be released as fizzing on the electrode, often oxidised as it loses
than water to oxygen is produced.
electrons.
cations = positive --> go to --> cathode = negative Reactive electrodes:
Usually, unreactive electrodes such as graphite or platinum are used, but sometimes reactive electrodes
anions = negative --> go to --> anode = positive such as copper electrodes in copper sulphate(aq) are used (the electrode and the metal ions in solution
are the same. In this case, the metal anode loses mass as it changes into ions and goes into solution.
It oxidises at the anode… - Cu(s) --> Cu2+(aq) + 2e-
Electrolysis of… And its reduced (deposited) at the cathode - Cu2+(aq) + 2e- --> Cu(s)
molten compounds
Predictions of electrolysis of SOLUTIONS:
solutions
Product at cathode Product at anode Loss at anode
All electrodes Unreactive electrode e.g. graphite Reactive electrode e.g. copper
Reduction Oxidation Oxidation
Hydrogen if metal is group 1,2 or Al Halogen if salt is a halide Anode loses mass as ions go into solution
Electrolysis of solutions:
Electrolysis of solutions is much easier than the electrolysis of molten compounds, 2H20(l) + 2e- --> 2OH-(aq) + H2(g) 2Cl-(aq) --> Cl2(g) + 2e- Cu(s) --> Cu2+(aq) + 2e-
when ionic compounds dissolve they become free to move, there is a different
apparatus for electrolysis of solutions in order to collect the gases produced. Metals for all other salts Oxygen is salt is sulphate or nitrate
Water takes part, which makes predictions more difficult, the water competes with n/a
the ions from the salt at the electrodes. Water can be both reduced at the cathode Mg2+(aq) + 2e- --> Mg(s) 2H2O(l) --> O2(g) + 4H+(aq) + 4e-
Chemistry Page 1
28 May 2024 14:46
ES1 Chemistry of Halogens
Halogens are p-block elements in group 7, they have seven electrons in the outer shells and are Reactions of halogens with halide ions:
the most reactive non-metals. They are found most naturally in compounds and the most The more reactive halogen will displace the less reactive halide and take its place.
abundant halogens are fluorine and chlorine however all of them are diatomic. They achieve These are often shown as ionic equations, where the spectator ions are removed, or
stability via ionic or covalent bonding. half equations, which show the loss/gain of electrons. These displacement reactions
are also redox reactions as both oxidation and reduction has occurred. Colour
changes can be difficult to see, adding an organic solvent makes the change more
Properties down the group:
distinct.
- Darker in colour - Gas --> Liquid --> Solid
- Melting and boiling point increases - Less volatile
Reaction of halide ions:
Reaction of halide ions with silver nitrate:
Solubility: Reactions with silver nitrate and halide ions are precipitation reactions where a solid is
There is no set trend for solubility, but all halogens are more soluble in organic solvents than formed, in this case it is a silver halide where 'X' is the halogen;
in water and this also makes them more distinguishable.
Ag+ (aq) + X- (aq) --> AgX(s)
Colours of silver halides can be hard to distinguish so ammonia solution is added as the
solubility of them in ammonia decreases down the group.
Halogen Colour of silver halide
Halogens in water (L -> R) Halogens in cyclohexane (L -> R)
Chlorine White precipitate
Chlorine - pale green Chlorine - pale green Bromine Cream precipitate
Bromine - orange/yellow Bromine - orange/brown
Iodine Yellow precipitate
Iodine - brown Iodine - violet purple
Chemical properties and reactions: Halogen Colour of silver halide + ammonia
Halogens are very reactive, they tend to remove electrons from other elements to complete their solution
own outer shell. This makes them oxidising agents (get reduced as they gain an electron) and the Chlorine Colourless
elements at the top of the group are the strongest oxidising agents. This trend in because as the Bromine Clouded/translucent yellow
size of the atom increases the further away the outer shell is and they gain electrons less readily.
Iodine (more) opaque yellow
ES2 Oxidation states and redox
Oxidation is: Element Oxidation state
Reduction is:
- Loss of electrons - Gain of electrons Fluorine -1
- Gain of oxygen - Loss of oxygen Oxygen -2 except with F or in
- Increase in oxidation state - Decrease in oxidation state
peroxide ion (O22-)
Oxidation states: Chlorine -1 except with F or O
Oxidation states are numbers assigned to an element in a chemical which tells you how many electrons have been lost or gained compared to Bromine -1 except with F, O, Cl
the unreacted chemical. Oxidation states follow several rules:
Iodine -1 except with F, O, Cl,
- Elements always have an oxidation state of 0
Br
- Ions have the same oxidation state as their charge
- Charges of compounds must equal zero overall Hydrogen +1 except in metal
hydride
Some elements have constant oxidation states which can be used to work out other oxidation state of elements in a compound Group 1 +1
Group 2 +2
Aluminium +3
Oxidation states and systematic naming:
The systematic names have Roman numerals in brackets that show the oxidation state of the part of the compound when that element may
have different oxidation states e.g. sulphuric(VI) acid shows that the sulphur in the compound has a an oxidation state of +6.
Oxyanions are negative ions with an oxygen in, they are signalled by -ate and a Roman numeral to show oxidation state.
ES3 Electrolysis
Electrolysis of molten compounds: Reduction at the cathode:
Solid ionic compounds do not conduct electricity as ions are not free to move, At the cathode, there are metal ions from the salt AND water. More reactive metals remain as ions and
once they are molten then the charged ions are able to move around and carry a
the hydrogen gas is released by the reduction of water, less reactive metals are deposited on the
current.
cathode.
Positive metal cations migrate to the negative electrode, the cathode, and negative
Oxidation at the anode:
anions migrate to the positive anode. The hot molten metal will collect at the
At the anode, there are negative ions from the salt and the water, halides are more likely to be oxidised
bottom of the container, usually it is reduced and gains electrons and any gas
than water so a halogen is produced. Other anions such as sulphates or nitrates are less likely to oxidise
products will be released as fizzing on the electrode, often oxidised as it loses
than water to oxygen is produced.
electrons.
cations = positive --> go to --> cathode = negative Reactive electrodes:
Usually, unreactive electrodes such as graphite or platinum are used, but sometimes reactive electrodes
anions = negative --> go to --> anode = positive such as copper electrodes in copper sulphate(aq) are used (the electrode and the metal ions in solution
are the same. In this case, the metal anode loses mass as it changes into ions and goes into solution.
It oxidises at the anode… - Cu(s) --> Cu2+(aq) + 2e-
Electrolysis of… And its reduced (deposited) at the cathode - Cu2+(aq) + 2e- --> Cu(s)
molten compounds
Predictions of electrolysis of SOLUTIONS:
solutions
Product at cathode Product at anode Loss at anode
All electrodes Unreactive electrode e.g. graphite Reactive electrode e.g. copper
Reduction Oxidation Oxidation
Hydrogen if metal is group 1,2 or Al Halogen if salt is a halide Anode loses mass as ions go into solution
Electrolysis of solutions:
Electrolysis of solutions is much easier than the electrolysis of molten compounds, 2H20(l) + 2e- --> 2OH-(aq) + H2(g) 2Cl-(aq) --> Cl2(g) + 2e- Cu(s) --> Cu2+(aq) + 2e-
when ionic compounds dissolve they become free to move, there is a different
apparatus for electrolysis of solutions in order to collect the gases produced. Metals for all other salts Oxygen is salt is sulphate or nitrate
Water takes part, which makes predictions more difficult, the water competes with n/a
the ions from the salt at the electrodes. Water can be both reduced at the cathode Mg2+(aq) + 2e- --> Mg(s) 2H2O(l) --> O2(g) + 4H+(aq) + 4e-
Chemistry Page 1
