Valence electrons are the number of electrons in the outermost energy level of an atom. Valency is the number of electrons an atom needs to gain or lose in order to form a octet

Relationship between Valency and Number of Valence Electrons:
The valency of an element is closely related to the number of valence electrons present in its atom. Valency is the combining capacity of an element, which determines how many bonds it can form with other elements. Valence electrons are the electrons in the outermost shell of an atom, responsible for the element's chemical properties.

Number of Valence Electrons:
- The number of valence electrons an element has is determined by its position in the periodic table.
- Elements in the same group have the same number of valence electrons.

Valency:
- Valency is determined by the number of electrons an element needs to gain, lose, or share to achieve a stable electron configuration.
- Elements with a completely filled outer shell have a valency of 0.
- Elements tend to react in a way that allows them to achieve a stable electron configuration.

Relationship:
- The valency of an element is often equal to the number of valence electrons it needs to gain or lose to achieve a stable electron configuration.
- For example, elements in Group 1 of the periodic table have 1 valence electron and tend to lose this electron to achieve a stable configuration, resulting in a valency of 1.
- Similarly, elements in Group 17 have 7 valence electrons and tend to gain 1 electron to achieve stability, resulting in a valency of 1.
In conclusion, the relationship between the valency of an element and the number of valence electrons in its atom is crucial in understanding how elements interact with each other to form compounds.