Oxidation number

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Melody Haratian 2J
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Oxidation number

Postby Melody Haratian 2J » Sun Nov 15, 2020 10:36 pm

Hi guys! I’ve seen a couple of homework problems on oxidation numbers. Can someone explain what the oxidation number is and how you find it.

Andreas Krumbein 1L
Posts: 69
Joined: Wed Sep 30, 2020 10:00 pm

Re: Oxidation number

Postby Andreas Krumbein 1L » Sun Nov 15, 2020 10:46 pm

So essentially there are some rules for finding the oxidation number:
1. Atoms in their elemental state have an oxidation number of 0
2. Monatomic ions have oxidation numbers equal to their charge.
3. Oxygen's oxidation number =−2 except when in hydrogen peroxide (H2O2) , or a peroxide ion (O2−2) where it is −1 .
4. Hydrogen's oxidation number is +1 , except for when bonded to metals as the hydride ion forming binary compounds. In LiH , NaH , and CaH2 , the oxidation number is −1 .
5. Fluorine has an oxidation number of −1 in all of its compounds.
6. Halogens ( Cl , Br , I ) have negative oxidation numbers when they form halide compounds. When combined with oxygen, they have positive numbers. In the chlorate ion (ClO−3) , the oxidation number of Cl is +5 , and the oxidation number of O is −2 .
7. In a neutral atom or molecule, the sum of the oxidation numbers must be 0. In a polyatomic ion, the sum of he oxidation numbers of all the atoms in the ion must be equal to the charge on the ion.

Using this you can find the oxidation number of a compound. For example the oxidation state of chlorine in CLO4- is 7. For using this information in one of the sapling homework questions to approximate the most plausible lewis structure, the oxidation number exaggerates the ionic character of the bond by assuming all the bonded electrons are assigned to the most electronegative atom. So if the center atom is less electronegative than the outer atoms, the lewis structure that assigns the highest formal charge to the center atom would be the the most plausible according to this method.

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