Chemistry Unit 2 Module 4

Oxidation number is a method used for keeping track of electrons during a reaction which can be used to help balance equations. The oxidation number of any uncombined element is 0 and the oxidation number of any uncombined ion is the same as its charge. The sum of oxidation numbers in a molecule is 0 (or in a complicated ion is equal to the charge on the particle)

• Hydrogen usually has an oxidation number of +1
• Oxygen usually has an oxidation number of -2 except in peroxides when it is -1 and with fluorine & is posotive
• Elements get more electronegative (therefore more oxidising) as you go up & across the periodic table
• Fluorine always has an oxidation number of -1
• Group 1 elements always have oxidation number +1, group 2 always have +2 and Group 3 always have +3

A redox reaction is one were both a reduction and an oxidation occur. Most oxidation or reduction reactions are actually redox because for one molecule to be oxidised another must be reduced. Sometimes in a reaction a single element can be both reduced and oxidised this is called a disproportionation reaction.

OIL RIG - Oxidation is Loss (of electrons) Reduction Is Gain (of electrons).

A redox reaction is one were both a reduction and an oxidation occur. Most oxidation or reduction reactions are actually redox because for one molecule to be oxidised another must be reduced. Sometimes in a reaction a single element can be both reduced and oxidised this is called a disproportionation reaction.

OIL RIG - Oxidation is Loss (of electrons) Reduction Is Gain (of electrons).