In chemistry a polyatomic molecule is a molecule that consists only of atoms of a single element. Most are nonmetals; in fact, most nonmetals form polyatomic molecules. The majority are diatomic. These elements are so reactive that they will bond with themselves if they cannot bond with anything else. Do not forget that these elements may exist as atoms in other compounds!

These are the most common polyatomic molecules:

• H₂
• N₂
• O₂, O₃ and O₄ (O₃ is also known as ozone, and O₄ spontaneously decomposes into the diatomic form)
• F₂
• Cl₂
• Br₂
• I₂
• At₂ (theoretically; this element's compounds have not been investigated because of its radioactivity)

• S₈
• P₄ Because these two elements can (at least in theory) form complex macromolecules with endless numbers of atoms in them, they can also be considered polyatomic molecules.

• C_x
• Si_x (highly unstable) These two do not actually come in varieties with a predictable number of atoms, so an x is used. For silicon and carbon, the 2 molecule form is explosively unstable (because a quadruple covalent bond is unstable because of the bending of orbitals), so the only form would be either some complex lattice (eg. a diamond) or a cycloalkene or cyclosilene with only double bonds, or some other form with alternating single and triple bonds.