The valency of an element depends upon the

The valency of an element is defined as its combining capacity, which is determined by the number of valence electrons present in the outermost shell of its atom. Atoms react to achieve a stable noble gas configuration, often following the octet rule [1]. This stability is reached by gaining, losing, or sharing electrons from the outermost shell [2]. For instance, carbon shares its four valence electrons to form covalent bonds, while chlorine, with seven electrons in its outermost shell, has a valency of one because it needs one more electron to complete its octet [2]. In contrast, the number of protons determines the atomic number and identity of the element, while the mass number is the sum of protons and neutrons; neither of these directly dictates the chemical combining capacity or valency.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 60