Redox

• An oxidation number is the number of electrons an atom uses to bond with any other atom
• The oxidation number of an uncombined element such as C, H, O2 is 0
• The oxidation number of combined oxygen such as in H2O is -2
• The oxidation number of oxygen in peroxides is -1
• The oxidation number of combined hydrogen such as in NH3, H2S is +1
• The oxidation number of hydrogen in metal hydrides such as LiH is -1
• The oxidation number of a simple ion is the charge on the ion. For example, Na+ → +1 ; Cl- → -1
• The oxidation number of combined fluorine such as in NaF, CaF2 is -1
• When an element has more than one stable oxidation number, it is indicated by being written as a Roman numeral
• The oxidation number of Fe in iron (III) chloride is +3
• Oxyanions are negative ions that have an element along with oxygen
• The oxidation number of S in SO42- is +6. This is because combined oxygen has an oxidation number of -2. 4 x -2 = -8. The charge on the compound is -2. The sum of oxidation numbers must equal -2. So, -2 -(-8) = +6
• Oxidation is the loss of electrons and an increase in oxidation number
• Reduction is the gain of electrons and a decrease in oxidation number
• A redox reaction is a reaction in which both oxidation and reduction take place
• The oxidation number of a metal is 0, because it is an uncombined element