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+---
+header-includes:
+- \usepackage[version=4]{mhchem}
+---
+
+# Electrochemistry
+
+## Oxidation states
+
+Indicates charge (ionisation) of an element
+
+**Oxidation** - loss of e-  
+**Reduction** - gain of e-
+
+Main group elements (i.e. group 2) - generally one oxidation state:
+
+| elements      | valence config | oxidation state |
+| ------------- | -------------- | --------------- |
+| alkali metals | $s^1$          | +1              |
+| alkali earths | $s^2$          | +2              |
+| aluminium     | $s^2 p^1$      | +2              |
+| nitrogen      | $s^2 p^3$      | -3              |
+| oxygen        | $s^2 p^4$      | -2              |
+| halogens      | $s^2 p^5$      | -1              |
+| noble gases   | $s^2,\>s^2p^5$ | n/a             |
+
+Transition metals (d shell) may have several oxidation states.
+
+$$\ce{H_2}$$
+
+Common oxidation numbers:
+
+| elements          | common ox. no. in compounds | exceptions          |
+| ----------------- | --------------------------- | ------------------- |
+| main group metals | valency                     | no                  |
+| hydrogen          | +1                          | metal hydrides (-1) |
+| oxygen            | -2                          |
+
+
+### Rules for oxidation states
+
+- oxidation states >3 may only exist in compounds
+- oxidation number of free element is 0
+- oxidation number of simple ion is the charge of the ion
+- sum of oxidation numbers in polyatomic ion is the charge of the ion
+- sum of oxidation numbers of a neutral compound is zero