Organic Chemistry

18 CHAPTER 1 Electronic Structure and Bonding • Acids and Bases

SOLUTION TO 10b The total number of valence electrons is 17 (5 for N and 6 for each

of the two O’s). Because the species has one positive charge, we must subtract 1 from the

number of valence electrons, for a total of 16. The 16 electrons are used to form bonds and

fill octets with lone-pair electrons.

Two double bonds are necessary to complete N’s octet. The N has a formal charge of

PROBLEM 11

a. Draw two Lewis structures for b. Draw three Lewis structures for

(Hint:The two Lewis structures in part a are constitutional isomers; they have the same

atoms, but differ in the way the atoms are connected. The three Lewis structures in part b

are also constitutional isomers.)

PROBLEM 12

Expand the following condensed structures to show the covalent bonds and lone-pair

electrons:

a. c.

b. d.

1.5 Atomic Orbitals

We have seen that electrons are distributed into different atomic orbitals (Table 1.2).

An orbitalis a three-dimensional region around the nucleus where there is a high

probability of finding an electron. But what does an orbital look like? Mathematical

calculations indicate that the satomic orbital is a sphere with the nucleus at its center,

and experimental evidence supports this theory. The Heisenberg uncertainty

principlestates that both the precise location and the momentum of an atomic particle

cannot be simultaneously determined. This means that we can never say precisely

where an electron is—we can only describe its probable location. Thus, when we say

that an electron occupies a 1satomic orbital, we mean that there is a greater than 90%

probability that the electron is in the space defined by the sphere.

Because the average distance from the nucleus is greater for an electron in a 2s

atomic orbital than for an electron in a 1satomic orbital, a 2satomic orbital is repre-

sented by a larger sphere. Consequently, the average electron density in a 2satomic or-

bital is less than the average electron density in a 1satomic orbital.

An electron in a 1satomic orbital can be anywhere within the 1ssphere, but a 2satom-

ic orbital has a region where the probability of finding an electron falls to zero. This is

called a node, or, more precisely—since the absence of electron density is at one set dis-

tance from nucleus—a radial node. So a 2selectron can be found anywhere within the

2 ssphere—including the region of space defined by the 1ssphere—except in the node.

(CH 3 ) 2 CHCl (CH 3 ) 3 C(CH 2 ) 3 CH(CH 3 ) 2

CH 3 NHCH 2 CH 3 (CH 3 ) 2 CHCHO

C 2 H 6 O. C 3 H 8 O.

N

+

OO

+1.

OON

2 s atomic orbital

node shown

z

x

y

2 s atomic orbital

node not shown

z

x

y

z

x

node

1 s atomic orbital

y