This refers to a bond holding two atoms together formed when electrons orbit both atoms. Effectively, the atoms "share" electrons in order to make sure their outer shells have the correct number of electrons to be full. Usually covalent compounds include non-metallic elements such as carbon or nitrogen. Diatomic : An element is said to be diatomic if its atoms are found in molecules consisting of two atoms each. Gases such as oxygen (O2), nitrogren (N2) and hydrogen (H2) are diatomic when they are elements. Also, all halogens are diatomic: Fluorine, F2, Chlorine, Cl2, Bromine, B2 and Iodine, I2.