Homonuclear diatomic molecules are composed of only one element.
Diatomic molecules are composed of only two atoms, of either the same or different chemical elements. Common diatomic molecules include hydrogen (H2), nitrogen (N2), oxygen (O2), and carbon monoxide (CO). Seven elements exist as homonuclear diatomic molecules at room temperature: H2, N2, O2, F2, Cl2, Br2, and I2. The bond in a homonuclear diatomic molecule is non-polar due to the electronegativity difference of zero.