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    • Thread Starter

    hi guys, can somebody explain oxidation state please?
    in molecules such as V2O5, O has -2, and V is +5, what does this mean??

    The oxidation numbers of a molecule must 'balance out' - i.e. (5x2)+(-2x5) =0 .. oxidation numbers are used to show whether an element is being oxidised or reduced- if the oxidation number increases in an equation this shows that the element has been oxidised (it has lost electrons) or if the oxidation number decreases then the element has been reduced (gained electrons- by gaining electrons it's oxidation number has become more negative).

    The oxidation numbers of some elements come from electronic configurations (I think!) for example, oxygen has an oxidation number of -2 because it gains 2 electrons to gain a full outer shell.. however many oxidation numbers change depending on what they're being combined with.. some other 'constant' ones are Mg and Ca (+2) Al (+3) F(-1)

    Hope this has answered your question
    • Study Helper

    Study Helper
    The previous post has already explained this quite well, I suppose. Just wanted to add...
    Atoms in a compound are assigned oxidation numbers based on the charge of the atom had all the bonds in it been 100% ionic. Of course this doesn't exist in reality, but it helps you with figuring things out such as whether something has been oxidized or reduced in a chemical reaction. In oxidation the oxidation number goes up and in reduction it goes down.
    Most elements have more than one oxidation state, an obvious example is iron, but there are many others.
    The oxidation number is defined as follows:
    1.Uncombined elements have an oxidation number of 0.
    2.For simple ions the oxidation number equals the charge.
    3.For most compounds hydrogen is +1 and oxygen is -2, there are exceptions with hydrides and peroxides however.
    4.The sum of all oxidation numbers in a compound is equal to its charge.
    So the trick is to learn all those rules and be able to apply them, and know what are the exceptions.
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