Page 89 - Theory and Problems of BEGINNING CHEMISTRY

78 CHEMICAL BONDING [CHAP. 5

5.6. How many electrons are there in the outermost shell of each of the following: (a) Ba, (b)P,(c) Pb,
(d) F, and (e) Xe?
Ans. (a)2 (b)5 (c)4 (d)7 (e)8

5.7. Which elements acquire the electronic configuration of helium by covalent bonding?
Ans. Only hydrogen. Lithium and beryllium are metals, which tend to lose electrons (and form ionic bonds) rather
than share. The resulting configuration of two electrons in the first shell, with no other shells occupied, is
stable. Second-period elements of higher atomic number tend to acquire the electronic configuration of neon.
If the outermost shell of an atom is the first shell, the maximum number of electrons in the atom is 2.

5.8. How does beryllium achieve the octet configuration?
Ans. Beryllium loses two electrons, leaving it with the electronic configuration of He. A configuration of two
electrons in its outermost shell corresponds to the “octet” because the new outermost shell is the first shell,
which can hold only two electrons.

5.9. How many electrons can fit into an atom in which the outermost shell is the (a) first shell, (b) second
shell, (c) third shell, and (d) fourth shell?

Ans. (a)2.The first shell is filled. (b) 10. The first and second shells are both filled. (c) 18. The first and second
shells are filled, and there are eight electrons in the third shell (the maximum number before the fourth shell
starts filling). (d)36 (2 + 8 + 18 + 8)

5.10. Compare the number of electrons in Problem 5.9 with the atomic numbers of the first four noble gases.
Ans. They are the same—2, 10, 18, and 36.

5.11. Explain why uncombined atoms of all the elements in a given main group of the periodic table will be
represented by a similar electron dot notation.
Ans. They all have the same number of valence electrons.

IONS
5.12. What is the difference between ClO 2 and ClO 2 ?
−
Ans. The first is a compound and the second is an ion—a part of a compound.

5.13. (a) What is the charge on the aluminum atom? (b) What is the charge on the aluminum ion? (c) What is
the charge on the aluminum nucleus?
Ans. (a)0 (b)3+ (c)13+
Note how important it is to read the questions carefully.

3+
5.14. When an aluminum atom loses three electrons to form Al , how many electrons are there in what is
now the outermost shell? in the valence shell?
Ans. There are eight electrons in the second shell, which is now the outermost shell, since the three electrons in
the third shell have been lost. There are now zero electrons in the valence shell.

5.15. (a) You have been given a stack of $2.00 gift certificates for a store which gives no change for these
certificates. What is the minimum number of $3.00 items that you can buy without wasting money? How
many certificates will you use? (b) Suppose the items were $4.00 each?
Ans. (a) You can buy two items (for $6) with three certificates (worth $6). (b) You can buy one item with two
certificates.