Here's why:

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

* In a covalent bond, atoms share electrons to achieve a stable electron configuration (like a noble gas).

* Since both nonmetals have a strong pull on electrons, they're more likely to share rather than one atom completely taking an electron from the other (which would form an ionic bond).

Examples of atoms that commonly form covalent bonds:

* Hydrogen (H)

* Carbon (C)

* Oxygen (O)

* Nitrogen (N)

* Fluorine (F)

* Chlorine (Cl)

* Bromine (Br)

* Iodine (I)

Note: There are some exceptions to this rule. For example, a metal like boron can sometimes form covalent bonds.