--- /dev/null
+---
+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