Valency vs Oxidation Number: Definitions, Differences & Examples

The charge of the main atom in a coordination molecule, if all the bonds surrounding it were ionic bonds, is known as the oxidation number. In practically all cases, transition metal atoms make up the bulk of coordination complexes. Chemical compounds known as ligands encircle this metal atom. 

To establish coordination bonds with metal atoms, these ligands can share their lone electron pairs with them. It resembles a covalent bond once the coordination bond has formed. This is because, similar to a covalent link, the two atoms in a coordination bond share a pair of electrons. However, the coordination bonds are treated as ionic bonds for calculating the central metal atom's oxidation number.

The metal atom's orbitals must be vacant for coordination bonds to form. The majority of the d orbitals in transition metals are vacant. They can therefore serve as the main metal atom in coordination complexes. Roman numbers are used to signify the central atom's oxidation number. The Roman number, enclosed in brackets, indicates the charge of the primary atom. If a hypothetical metal atom "M" has an oxidation number of 3, for instance, the oxidation number is expressed as M(III).

Find the Oxidation Number of an Atom:

The number of electrons an atom or ion has either gained or lost in comparison to the neutral atom is known as the oxidation number or state of the atom or ion. The number of electrons lost by each electropositive metal atom in groups 1, 2, and 3 is fixed, and their positive oxidation numbers are always positive.

More electronegative atoms in molecules receive electrons from less electronegative atoms, resulting in negative oxidation states. The number of electrons lost or acquired determines the oxidation state's numerical value.

An atom or ion in a molecule or ion's oxidation number or oxidation state is determined by:

• Compiling the constant oxidation states of all the atoms, molecules, and ions linked to it.

• Comparing the total charge of a molecule or an ion to its total oxidation state.

What is Valency?

The maximum number of electrons that an atom can gain, share, or lose before stabilizing is known as valency. The octet rule specifies the most stable form of an atom for both metals and nonmetals. It claims that a configuration is stable if an atom's outermost shell is filled with eight electrons. 

In other words, it is stable if the s and p sub-orbitals are filled with ns2np6. This arrangement of electrons naturally exists in noble gas atoms. Therefore, for additional elements to follow the octet rule, they must either gain, lose, or share electrons. The valency of that atom refers to the maximal number of electrons engaged in this stabilization process.

As an illustration, the electron configuration for the element silicon is 1s22s22p63s23p2. n = 3 for the outermost shell. That shell contains four electrons. To complete the octet, it must therefore acquire 4 extra electrons. To complete the octet, silicon typically needs to share 4 electrons with other elements.

Find the Valency of an Atom:

As is knowledge, magnesium has two electrons in its outermost shell compared to one for hydrogen. Since hydrogen is easily capable of losing one electron and becoming stable, its valency is 1. Magnesium, on the other hand, has a value of 2 since it can lose 2 electrons with ease and also achieve stability.

Additionally, it is not just based on the loss of an electron by an atom. For instance, the outermost orbital of fluorine has 7 electrons. Since losing 7 electrons is difficult, it gains 1 electron to finish out its octet. It acquires 1 electron, making its valency 1. The elements in the same group of the periodic table have the same valency.

For example, all of the elements in group 8 have 8 electrons and filled orbitals, hence all of the elements in this group have zero valencies.

Difference Between Valency and Oxidation Number:

The valence electrons of an atom are associated with the concepts of oxidation number and valency. The main difference between valency and oxidation number is that the former refers to the maximum number of electrons an atom can lose, gain, or share to stay stable. In contrast, the latter refers to the number of electrons an atom can gain or lose to establish a bond with another atom. Furthermore, the phrase "valency" refers to any chemical element, but the term "oxidation number" refers primarily to coordination complexes. Lets now differentiate between valency and oxidation  number:

Summary

Valency and oxidation number are two terms that are often confused, but they have different meanings. Valency is the number of electrons that an atom can lose, gain, or share to form a chemical bond. Oxidation number is the charge that an atom would have if all of its bonds were ionic. The main difference between valency and oxidation number is that valency is a property of an individual atom, while oxidation number can vary depending on the molecule or ion that the atom is a part of. In general, valency is a more fundamental property than oxidation number, and it is often used to predict the types of chemical bonds that an atom can form. Oxidation number, on the other hand, is a more useful concept for understanding the reactivity of molecules and ions.