What are oxidation numbers?

Numbers given to each atom or ion in a compound to show its degree of oxidation.


Oxidation numbers are also called oxidation states.

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What is the oxidation number of any uncombined element?

Zero

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What is the oxidation number of group 1 ions?

+1

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What is the oxidation number of group 2 ions?

+2

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What is the sum of the oxidiation numbers in a compound?

Zero

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What is the sum of the oxidiation numbers in an ion equal to?

The charge on the ion.

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What is the oxidation number of hydrogen in most compounds, and when is there an exception to this rule?

+1, except in metal hydrides where it is -1. 

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What is the oxidation number of oxygen in most compounds, and when are there exceptions to this rule?

-2, except for in peroxides where it is -1 and in the compound OF2 where it is +2.

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What is the oxidation number of an element in a monatomic ion?

The charge on the ion.


For example, the oxidation number of oxygen in O2- is -2. 

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In a compound or ion containing 2 non-metals, how do you deduce which element is given the negative oxidation number?

The negative oxidation number is given to the more electronegative element.


For example, the oxidation number of oxygen in H2O is -2 because oxygen is more electroegative than hydrogen.

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Which element always has an oxidation number of -1?

Fluorine always has an oxidation number of -1 because it is the most electronegative element.

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