Here's why:

* Valence electrons are the electrons in the outermost energy level of an atom.

* They are the furthest from the nucleus and experience the weakest attraction to it.

* This makes them more easily influenced by other atoms, allowing them to be gained, lost, or shared in chemical reactions.

* The number of valence electrons determines an atom's chemical properties and its ability to form bonds with other atoms.

Example:

Sodium (Na) has one valence electron. This electron is readily lost, making sodium highly reactive and prone to forming ionic bonds with other elements.

In contrast, the inner electrons are tightly bound to the nucleus and are not involved in chemical reactions.