Covalent bonding occurs when atoms share valence electrons to form a chemical bond. Atoms of nonmetals form covalent bonds by sharing electrons in order to achieve an octet of valence electrons, like the noble gases, except for helium, which only has two valence electrons. The octet refers to the highest energy s and p sublevels, the valence shell, which in noble gases, except for helium, are filled with eight electrons, two in the s sublevel and six in the p sublevel.
