Exceptions to the Octet Rule
Exception # 1 - not enough valence electrons
H
H
H
C•
C
H
methyl radical
(7 valence electrons)
H
• O
N
H
methyl cation
(6 valence electrons)
nitrogen oxide
(11 valence electrons)
Exception # 2 - early second row elements (Be, B)
H
H Be H
beryllium hydride
(Be shares 4 electrons)
H
B
H
borane
(B shares 6 electrons)
Exceptions to the Octet Rule
Exception # 3 - beyond the second row, elements can
be surrounded by more than eight electrons (valence
shell expansion)
H3PO4
phosphoric acid
O
P O H
H O
O H
phosphoric acid
(P shares 10 electrons)
Under NO circumstances can the second row elements
be surrounded by more than eight electrons:
B, C, N, O, F