What is valency? How does it differ from the oxidation state?

What is valency? How does it differ from the oxidation state? Give examples of substances in which the values of the oxidation state and valence of atoms are numerically the same and different.

Valence is a property of an element that determines the number of other atoms with which an atom of an element can combine. Introduced in 1868, this term is used to express both the cardinality of the combination of an element as a whole, and the numerical value of the cardinality of the combination.

Valence is the number of electrons on its outer shell or its atomic charge, some elements have several charges, like sulfur, -2, +4, +6 and nitrogen +5, -3. A negative charge means the elements require even more electrons to fill its shell, like nitrogen, so it still needs 3 electrons. A positive charge means how many electrons it wants to lose, like sodium, it is +1 charged, so it wants to lose electrons.

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