Question

Elements of group $1$ and elements of group $17$ both have valency $1$. Explain.

Answer 1

Valency depends on the number of electrons in the outermost (valence) shell.

• Group $1$ elements have $1$ electron in their outermost shell, so they can donate $1$ electron to other elements to attain a stable configuration. Thus, they possess valency $1$.
• Group $17$ elements have $7$ electrons in their outermost shell, so they can accept only one electron from the combining atom to attain a stable configuration. Thus, group $17$ elements possess valency $1$.