Here's why:

* Nonmetals have a high electronegativity, meaning they have a strong attraction for electrons.

* Covalent bonds involve the sharing of electrons between atoms.

* Since both nonmetals have a strong pull on electrons, they are most likely to share electrons rather than one completely transferring an electron to the other (which is what happens in ionic bonds).

Examples of covalent bonds between nonmetals:

* Oxygen (O2) - Double covalent bond

* Water (H2O) - Single covalent bonds

* Carbon dioxide (CO2) - Double covalent bonds

* Methane (CH4) - Single covalent bonds