Here's why:

* Valence electrons are the electrons in the outermost energy level of an atom. They are the ones most loosely bound to the nucleus and therefore most likely to participate in chemical bonding.

* Inner shell electrons are closer to the nucleus and are more tightly bound. They are not involved in bonding.

Bonding Basics:

* Covalent Bonds: Atoms share valence electrons to achieve a stable electron configuration.

* Ionic Bonds: Atoms transfer valence electrons from one atom to another, resulting in the formation of ions with opposite charges.

Example:

* Oxygen (O) has 6 valence electrons. It needs 2 more electrons to achieve a stable octet (8 electrons in its outer shell). Oxygen can form two covalent bonds by sharing its valence electrons with other atoms.