Page 75 - Theory and Problems of BEGINNING CHEMISTRY

64 ELECTRONIC CONFIGURATION OF THE ATOM [CHAP. 4

4.16. (a) How many orbitals are there in the fourth shell of an atom? (b) How many electrons can be held in
the fourth shell of an atom? (c) How many electrons can be held in the fourth shell of an atom before the
fifth shell starts to fill?
2
Ans. (a) 16 (one s orbital, three p orbitals, five d orbitals, and seven f orbitals). (b)2(4) = 32. (c) 8. (The
5s subshell starts to fill before the 4d subshell. Thus, only the 4s and the 4p subshells are filled before the
fifth shell starts.)

4.17. How many electrons are permitted in each of the following subshells?
n l n l

(a) 3 1 (c) 3 2
(b) 3 0 (d) 4 0
Ans. (a) 6. This is a p subshell (with three orbitals). (b) 2. This is an s subshell. (c) 10. This is a d subshell,
with five orbitals corresponding to m l values of −2, −1, 0, 1, 2. Each orbital can hold a maximum of 2
electrons, and so the subshell can hold 5 × 2 = 10 electrons. (d) 2. This is an s subshell. [Compare to
part (b).] The principal quantum number does not matter.

4.18. How many electrons are permitted in each of the following subshells? (a)2s (b)6p, and (c)4d.
Ans. (a)2 (b)6 (c) 10.
Note that the principal quantum number does not affect the number of orbitals and thus the maximum number
of electrons. The angular momentum quantum number is the only criterion of that.

4.19. In Chap. 3 why were electron dot diagrams drawn with four areas of electrons? Why are at least two of
the electrons paired if at least two are shown?

Ans. The four areas represent the one s plus three p orbitals of the outermost shell. If there are at least two electrons
in the outermost shell, the first two are paired because they are in the s subshell. The other electrons do not
pair up until all have at least one electron in each area (orbital).

SHAPES OF ORBITALS
4.20. Draw an outline of the shape of the 1s orbital.
Ans. See Fig. 4-4.

4.21. How do the three 2p orbitals differ from one another?
Ans. They are oriented differently in space. The 2p x orbital lies along the x axis; the 2p y orbital lies along the y
axis; the 2p z orbital lies along the z axis. See Fig. 4-4.

4.22. Toward which direction, if any, is each of the following orbitals aligned: (a)1s,(b)2p y , and (c)3d z ?
2
Ans. (a) None; it is spherically symmetric (b) Along the y axis (c) Along the z axis

4.23. Which 2p orbital of a given atom would be expected to have the greatest interaction with another atom
lying along the x axis of the first atom?

Ans. The 2p x orbital. That one is oriented along the direction toward the second atom.

BUILDUP PRINCIPLE
4.24. Write detailed electronic configurations for the following atoms: (a) Li, (b) Ne, (c) C, and (d)S.

2
2
2
Ans. (a)1s 2s 1 (c)1s 2s 2p 2
6
2
2
2
2
2
(b)1s 2s 2p 6 (d)1s 2s 2p 3s 3p 4