What is the importance of valency?

Explanation

1) An atom with 8 electrons or an octet in their outer most shell is chemically stable or does not combine other atoms. Ex : `Ne, Ar` etc.
2) An atom with duplet or 2 electrons in its outer most shell is also more stable when there is only one shell present in it. Ex : `He`
3) Atoms of an element thus react with other atoms. So as to achieve an octet in their shell.
4) When elements reacts to form compounds, their atoms must be combining in such a way that they can attain the stable electron distribution of noble gases or inert gases.