As was the case for Cl in HCl, the O atom in the Lewis structure of H2O and in Cl2O is surrounded by eight electrons (whan the bond-pair electrons are double counted). In attaining these eight electrons, the O atom conforms to the octet rule-a requirement of eight valence-shell electrons for the atoms in a Lewis structure. Note, however, that the H atom is an exception to this rule. The H atom can accommodate only two valence-shell electrons.