4.3 Redox

• An oxidation number has a + or - sign followed by a number
• In a pure element, the oxidation number is 0
• Fluorine always has an oxidation number of -1
• Redox reactions have oxidation and reduction happening at the same time
• Oxidation is the loss of electrons
• Reduction is the gain of electrons
• Oxidation is an increase in oxidation number
• Reduction is a decrease in oxidation number
• Redox reactions occur between metals and acids
• Half equations represent the transfer of electrons in a reaction