Here's why:

* Sharing electrons: Covalent bonds involve the sharing of electrons between two atoms. This sharing creates a strong attraction between the atoms, holding them together.

* Stable molecules: By sharing electrons, atoms achieve a more stable electronic configuration, which is the driving force behind bond formation.

* Diverse structures: Covalent bonds can form in various ways, leading to a wide diversity of molecules with different shapes and properties.

Examples of molecules formed by covalent bonds:

* Water (H₂O): Two hydrogen atoms share electrons with an oxygen atom.

* Carbon dioxide (CO₂): A carbon atom shares electrons with two oxygen atoms.

* Glucose (C₆H₁₂O₆): A complex molecule with many covalent bonds between carbon, hydrogen, and oxygen atoms.

* DNA: A very large molecule held together by covalent bonds between numerous atoms.

In short, covalent bonds are the glue that holds atoms together to create the vast array of molecules that make up our world.