2d465e272b8a75b9bb6627685468b27830f7aa99
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   3- \usepackage[version=4]{mhchem}
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   5
   6# Electrochemistry
   7
   8## Oxidation states
   9
  10Indicates charge (ionisation) of an element
  11
  12**Oxidation** - loss of e-  
  13**Reduction** - gain of e-
  14
  15Main group elements (i.e. group 2) - generally one oxidation state:
  16
  17| elements      | valence config | oxidation state |
  18| ------------- | -------------- | --------------- |
  19| alkali metals | $s^1$          | +1              |
  20| alkali earths | $s^2$          | +2              |
  21| aluminium     | $s^2 p^1$      | +2              |
  22| nitrogen      | $s^2 p^3$      | -3              |
  23| oxygen        | $s^2 p^4$      | -2              |
  24| halogens      | $s^2 p^5$      | -1              |
  25| noble gases   | $s^2,\>s^2p^5$ | n/a             |
  26
  27Transition metals (d shell) may have several oxidation states.
  28
  29$$\ce{H_2}$$
  30
  31Common oxidation numbers:
  32
  33| elements          | common ox. no. in compounds | exceptions          |
  34| ----------------- | --------------------------- | ------------------- |
  35| main group metals | valency                     | no                  |
  36| hydrogen          | +1                          | metal hydrides (-1) |
  37| oxygen            | -2                          |
  38
  39
  40### Rules for oxidation states
  41
  42- oxidation states >3 may only exist in compounds
  43- oxidation number of free element is 0
  44- oxidation number of simple ion is the charge of the ion
  45- sum of oxidation numbers in polyatomic ion is the charge of the ion
  46- sum of oxidation numbers of a neutral compound is zero