Atomic Structure - Valency

Valency is defined as the combining capacity of an atom of an element with other atoms to form molecules.

The electrons present in the outermost shell of an atom are called valence electrons. These electrons determine the valency of the element.

The Octet Rule states that atoms tend to gain, lose, or share electrons to achieve a stable configuration of $8$ electrons in their outermost shell (or $2$ in the case of the $K$ shell, known as a duplet).

Metals typically have $1$, $2$, or $3$ valence electrons and lose them to achieve stability, forming positively charged ions called $cations$.

Non-metals typically have $5$, $6$, or $7$ valence electrons and gain electrons to achieve stability, forming negatively charged ions called $anions$.

Noble gases like Helium ($He$), Neon ($Ne$), and Argon ($Ar$) have a valency of $0$ because their outermost shells are completely filled.

Variable Valency: Some elements, particularly transition metals, exhibit more than one valency. For example, Iron ($Fe$) can show valencies of $2$ ($Ferrous$) and $3$ ($Ferric$).