The Lewis model of the simple covalent bond

The Lewis model is based on the octet rule and concerns simple molecules without transition elements, for instance: The Lewis model concerns also simple multiatomic ions, for example: Green: The outer electrons of the neutral atoms Red: The supplementary electrons which are responsible for the charge of the ion.

The atoms form as many covalent bonds as they have outer unpaired electrons


The oxygen atom O has to unpaired electrons able to form two covalent bonds in the water molecule, whereas the hydroxide ion has only a single unpaired electron left to form a covalent bond!