Oxidation is the loss of electrons, reduction is the gain of electrons (OILRIG)
The oxidation number of an atom is the charge that would exist on an individual atom if the bonding was completely ionic
In molecules/compounds the sum of oxidation numbers of the atoms is zero
In complex ions, the sum of the oxidation numbers on the atoms is equal to the overall charge on the ion e.g. ClO-, oxidation number of Cl = +1, oxidation number of O = -2, +1 + (-2) = -1
All group I atoms adopt a +1 oxidation state in their compounds
All group II atoms adopt a +2 oxidation state in their compounds
Aluminium always adopts a +3 state
Fluorine always adopts a -1 state
Hydrogen adopts a +1 state, unless bonding to metal, silicon, or boron in which it adopts a -1 state
Oxygen adopts a -2 oxidation state unless bonded to a group I/II metal, or hydrogen, in which it adopts a -1 state, or which fluorine, in which it adopts a +2 state
The oxidation state of all other atoms varies depending on the compound
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Oxidation & Reduction 2
If an atom is oxidised its oxidation state increases
If an atom is reduced its oxidation state decreases
How to balance half equations
Indentify the atom being oxidised or reduced, make sure there are the same number of that atom on both sides
Balance O atoms by adding H2O
Balance H atoms by adding H+
Add the electrons to ensure the charge on both sides is the same
Oxidising agents accept electrons from other species
Reducing agents give away electrons to other species
The simultaneous oxidation and reduction of the same species is known as disproportionation
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Halogens & Halides
Elements in group VII - fluorine, chlorine, bromine, and iodine
Tend to form diatomic molecules - F2, Cl2, Br2, and I2
These form anions called halides
Boiling point increases down the group due to increase in strength of Van der Waal's forces
The electronegativity decreases down the group
All halogens are oxidising agents
Fluorine is the best oxidising agent, followed by chlorine
Halide ions are reducing agents
Iodide ions are the best reducing agents, followed by bromine ions
Fluoride ions have no significant reducing properties
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