In this case, the oxygen has an oxidation state of +2. The problem here is that oxygen isn't the most electronegative element. The oxidation number of oxygen in compounds is usually -2. H +1 2 O -1 2 → H +1 2 O -2 + O 0 2 b) Identify and write out all redox couples in reaction. In H 2O, the hydrogen atoms each have an oxidation number of +1, while the oxygen has an oxidation number of −2, even though hydrogen and oxygen do not exist as ions in this compound as per rule 3. 9. Since each hydrogen has an oxidation state of +1, each oxygen must have an oxidation state of -1 to balance it. The oxidation number of an element in its elemental state is 0. Oxygen can take multiple oxidation states. So you then work backwards, deciding if it's $\ce{Na+}$ then you have +2 from the sodium, and oxygen must have an average oxidation number of -1 per oxygen atom. Answered By Answer and Explanation: The given chemical compound is oxygen gas {eq}\left( {{\text{O}}_{2}} \right) {/eq}. The rules are that the oxidation number of combined oxygen is -2, except in peroxides like H2O2, where it is -1. In its compounds, Oxygen usually has an oxidation number of -2 , O^-2 Oxygen has an electron configuration of 1s^2 2s^2 2p^4 To complete its valence shell and satisfy the octet rule, the oxygen atom will take on two electrons and become O^-2. The oxidation number of combined hydrogen is +1, except in hydrides like NaH, where it is -1. Re: Oxidation Numbers for O2 and O3 Post by Katherine Jabba 2H » Thu Feb 04, 2016 8:31 pm The oxidation number for elements in their natural … In NaCl, sodium has an oxidation number of +1, while chlorine has an oxidation number of −1, by rule 2. Exceptions include molecules and polyatomic ions that contain O-O bonds, such as O 2, O 3, H 2 O 2, and the O 2 2-ion. This particular compound is sodium peroxide.. You're right that usually oxygen has a charge of -2, but in this case, there's no way that each $\ce{Na}$ can have an oxidation state of +2.. For a neutral chemical compound, the oxidation numbers of the individual atoms must add up to a total of zero. Oxidation of oxygen are as follows: ( − 1 ) B a O 2 , ( − 2 1 ) K O 2 , ( 0 ) O 3 , ( + 2 ) O F 2 . The elements in Group VIIA often form compounds (such as AlF 3, HCl, and ZnBr 2) in which the nonmetal has a -1 oxidation number. 8. Oxidation number (also called oxidation state) is a measure of the degree of oxidation of an atom in a substance (see: Rules for assigning oxidation numbers). The fluorine is more electronegative and has an oxidation state of -1. The oxidation number of a Group IA element in a compound is +1. Oxygen usually has an oxidation number of -2. In peroxides, such as "H"_2"O"_2, "Na"_2"O"_2, and "BaO"_2", each oxygen atom has an oxidation number of -1. The oxidation number for oxygen is −2 unless it is in oxygen gas, ozone (O 3), or a peroxide (a compound containing the O 2 2− ion, where the oxidation number for oxygen is −1). Exceptions include OF 2 because F is more electronegative than O, and BaO 2, due to the structure of the peroxide ion, which is [O-O] 2-. O2 is molecular oxygen and is composed of two oxygen … Oxygen in F 2 O. Mg + O2 ---> Mg2+ + O2- ---> MgO The oxidation numbers of pure Mg and O2 are 0. For example, the oxidation number of the oxygen atom in the water is -2. 7 0. So H = 0 in H2.