Here's why:

* Covalent bonds form when two atoms share electrons to achieve a stable electron configuration. This sharing creates a pool of electrons that both atoms can access.

* Ionic bonds involve the transfer of electrons, where one atom loses electrons and becomes positively charged, while the other gains electrons and becomes negatively charged. They are then held together by electrostatic attraction.

* Metallic bonds involve a "sea" of delocalized electrons that are shared by all the metal atoms in a solid. While electrons are pooled, it's not between two specific atoms like in a covalent bond.

Example: In a water molecule (H₂O), the oxygen atom shares electrons with each of the two hydrogen atoms, forming covalent bonds. This shared pool of electrons contributes to the overall stability of the water molecule.