Here's why:

* Electrons occupy the outermost energy levels of an atom (valence shell). These are the electrons involved in chemical reactions.

* Chemical bonds form by the sharing or transfer of electrons between atoms.

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

* Ionic bonds: One atom transfers electrons to another, resulting in oppositely charged ions that attract each other.

While protons and neutrons contribute to an atom's identity and stability, they don't directly participate in the formation of chemical bonds.