Define the term valency. How is valency different from valence electrons? Find the valency of oxygen and fluorine.

(N/A) Valency: The combining capacity of an atom of an element is known as its valency.
Difference from valence electrons: Valency is the combining capacity of an atom,whereas valence electrons are the number of electrons present in the outermost shell of an atom.
Valency of $O$ and $F$: The atomic number of oxygen $(O)$ is $8$,and its electronic configuration is $2, 6$. It needs to gain $2$ electrons to complete its octet,so its valency is $2$.
The atomic number of fluorine $(F)$ is $9$,and its electronic configuration is $2, 7$. It needs to gain $1$ electron to complete its octet,so its valency is $1$.