Question

What is the difference between valency and oxidation state?

Answer 1

According to the IUPAC definition valency is the “”maximum number of univalent atoms that may combine with the atom.” That means valency is given by the number of bonds which can be formed by an atom. The number of valence electrons that an atom has determined the valency of that atom. Valence electrons are the electrons in an atom which participate in the chemical bond formation. When chemicals bonds are forming, either atom can gain electrons, donate electrons or share electrons. The ability to donate, gain, or share depends on the number of valence electrons they have. For example, when a H₂ molecule is forming one hydrogen atom gives one electron to the covalent bond. Thus, two atoms share two electrons. So the valency of a hydrogen atom is one. Univalent atoms or groups like hydrogen and hydroxyl have a valency of one whereas divalent atoms or groups have a valency of two, etc.

According to the IUPAC definition, the oxidation state is “a measure of the degree of oxidation of an atom in a substance. It is defined as the charge an atom might be imagined to have.” Oxidation state is an integer value, and it can be either positive, negative or zero. The oxidation state of an atom is subjected to change upon chemical reaction. If the oxidation state is increasing, then the atom is said to be oxidized, and if it is decreasing, then the atom has undergone reduction. In the oxidation and reduction reaction, electrons are transferring. In pure elements, the oxidation state is zero.

• Valency is given by the number of bonds that a species can form.

• Oxidation state is the charge an atom or group can have.