Valency and Valence Electrons

Valency and Valence Electrons are integral parts of the valence shell, which is also known as the inert pair. The inert pair is an electron that does not form part of an orbital and is therefore not involved in bonding or sharing protons with another atom.

The presence of an inert pair in a compound has important consequences on the physical and chemical properties of the compound. In some cases the presence of the electron in this position can lead to covalent bonding (H-bonding) between two atoms.

What is Valency?

Valency is different from valence electron i.e. Valency is the capacity of an atom to form covalent bonds with other atoms. In contrast, Valence electrons are the number of electrons that are needed for a complete outer shell in a compound for bonding and sharing one or more protons with another atom.

Valency Shells

The valence shell contains 8 electrons. The first 5 can be found in the p-orbitals while the 2nd and 3rd lie in the s-orbital. 

What is Valence Electron?

Valence electrons are the central core of an atom. In general, there are eight valence electrons in an atom. These electrons are responsible for the formation of chemical bonds between different atoms. This is why it is important for a compound to have all its valence electrons present so that it forms a strong bond with another atom i.e. effectively sharing protons between the two atoms in question Here the electron is designated as σ-electron or s-pair or nonbonding pair. In fact, if a compound has its valence electron fully occupied (according to the theory) with bonding electrons, then this compound is called a covalent bond.

Valency and Valence Electrons: Difference 

1. Valency = Capacity to form a covalent bond, Valence = Number of electrons needed for a complete outer shell for bonding and sharing one or more protons with another atom.
2. Valency is a property of an atom whereas Valence is the number of electrons needed for a complete outer shell in a compound for bonding and sharing one or more protons with another atom.
3. Valency is the capacity of an atom to form covalent bonds with other atoms. In contrast, valence electrons are the number of electrons that are needed for a complete outer shell in a compound for bonding and sharing one or more protons with another atom.
4. Valency is the physical property whereas valence electrons are the central core of an atom.
5. Valency is the capacity to form covalent bonds with another atom. In contrast, Valence Electron = Non-Bonding Pair.
6. In the case of divalent and trivalent elements, valency is equal to valence i.e. two and three respectively, as these elements contain two and three electrons in their valence shells respectively.
7. A valence electron is a nonbonding pair whereas valence electron is basically present in all atoms, regardless of their element.
8. Valency and Valence Electrons are very important in bonding and sharing one or more protons between two atoms.
9.  Valence Electrons are the central core of an atom while they are not needed to form covalent bonds with other atoms. 
10. Valency and Valence electrons are described in a different ways i.e. they can be described as physical properties while valence is mainly used to describe the capacity of an atom to form covalent bonds with another atom.
11. Valency is the physical property of an atom while Valence Electrons are the central core of an atom.
12. Valency is a quantum property whereas valence electrons are essential for forming covalent bonds.
13. Valency and valence electrons are described in a different ways i.e. they can be described as physical properties while valence is mainly used to describe the capacity of an atom to form covalent bonds with another atom.
14. Valency = Capacity to form a covalent bond, Valence = Number of electrons needed for a complete outer shell for bonding and sharing one or more protons with another atom.

Conclusion

Valency and Valence Electrons are two different entities that are present in the valence shell of an atom (except for hydrogen which has only 1 electron in its valence shell). Valency is a physical property and is different from the number of electrons needed for a complete outer shell, which is known as a valence electron.