2.1.5 - redox

• An oxidation number is the number of electrons an atom uses to bond with any other atom
• The oxidation number of an in combined element such as C, H O2 is always 0
• The oxidation number of combined oxygen is -2
• The oxidation number of oxygen in peroxides is -1
• The oxidation number of combined hydrogen is +1
• The oxidation number of combined hydrogen in metal hydrides such as LiH is -1
• The oxidation number of a simple ion is the same as the charge on the ion

  eg Na+ —> +1
• The oxidation number of combined fluorine is -1
• when the element has more than one stable oxidation number it is written as a roman numeral
• The oxidation number of Fe in iron (III) chloride is +3
• what are oxyanions?

  negative ions that have an element along with oxygen
• The oxidation number of S in SO4 2- is +6

  because combined oxygen has an oxidation number of -2 (total of -8)

  the charge on the compound is -2 so sum of oxidation numbers must = -2

  so -2 -(-8) = +6
• Oxidation is loss of electrons or an increase in oxidation number
• Reduction is the gain of electrons or decrease in oxidation number
• A redox reaction is a reaction in which both oxidation and reduction takes place
• The oxidation number of a metal is 0 because it is an uncombined element