formula for oxidation number
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Hey !! You assign oxidation numbers to the elements in a compound by using the Rules for Oxidation Numbers. Explanation: The oxidation number of a free element is always 0. The oxidation number of a monatomic ion equals the charge of the ion. The oxidation number of H is +1, but it is -1 in when combined with less electronegative elements. The oxidation number of O in compounds is usually -2, but it is -1 in peroxides. The oxidation number of a Group 1 element in a compound is +1. The oxidation number of a Group 2 element in a compound is +2. The oxidation number of a Group 17 element in a binary compound is -1. The sum of the oxidation numbers of all of the atoms in a neutral compound is 0. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion. EXAMPLE: What is the oxidation number of Cr in CrCl 3 ? Solution: We use what rules we can to determine the oxidation numbers. Rule 7 states that the oxidation number of Cl is -1. We write the oxidation number of the element above its symbol and the total for 3 Cl atoms below the symbol. This gives Cr -1 Cl 3 m m m m m m l l -3 m m . Rule 8 states the numbers along the bottom must add up to zero. So the number under Cr must be +3. This gives Cr -1 Cl 3 m m m m m +3 l l -3 m m . There is only one Cr atom, so its oxidation number is +3. This gives + 3 Cr -1 Cl 3 m m m m m +3 l l -3 m m . The oxidation number of Cr in CrCl 3 is +3. Here is a chart showing the oxidation numbers of the atoms in some common elements and compounds.