II
Choices I and III must be wrong because, although they satisfy the octet rule, they have
the wrong total number of electrons; choice I has eight valence electrons, while choice III
has 12. Given two N atoms, there can be (2)(5) = 10 valence electrons, as in correct choice
II. Choice IV is doubly wrong because, in addition to having only eight total electrons, the
octet rule is not satisfied, as each nucleus has seven, not eight, valence electrons.B.
IV
Choice IV is the preferred structure, since four of the five atoms have a formal charge of
zero. Since Cl is in the third period, its number of valence electrons can exceed eight.C.
5 . II
In resonance forms, only the electrons change place; atoms are not rearranged. Choices I
and III are both resonance structures. Choice II requires rearrangement of the atoms.A.
II
By the same reasoning as above.B.
6 . D
There is no formal charge on the structure of choice A; therefore, this structure should be the
more likely resonance structure. However, the expanded octet on N makes the structure
impossible. Choice C is incorrect because the negative formal charge is on N, which is not the
most electronegative atom. Choice B is incorrect because O, which is the most electronegative
atom, has a formal charge of +2.D is most likely because the negative formal charge is on O, the more electronegative element.7 .
Note that a correct ionic Lewis structure must always show the charge on the ion.8 . [NO 3 ]–
has needs
charge: 1 electron