Page 94 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 5] CHEMICAL BONDING 83

The configuration for Pb 2+ is the same except for the loss of the outermost two electrons. There are four
electrons in the sixth shell; the two in the last subshell of that shell are lost first:
2
6
2
2
2
6
2
6
10
14
6
10
10
2
Pb 2+ 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4 f 5d 6p 0
In shortened terminology:
10
14
2
Pb [Xe] 6s 4 f 5d 6p 2
2
14
10
Pb 2+ [Xe] 6s 4 f 5d 6p 0
5.48. What ion with a double negative charge is represented by each of the following configurations:
6
2
6
2
2
2
2
6
(a)ls 2s 2p and (b)ls 2s 2p 3s 3p ?
Ans. (a)O 2− (b)S 2−
5.49. What positive ion with a double charge is represented by each of the following configurations:
2
6
2
5
2
6
2
2
6
6
2
(a)ls 2s 2p 3s 3p and (b)ls 2s 2p 3s 3p 3d ?
Ans. (a)Ca 2+ (b)Mn 2+
5.50. What is the difference in the electronic configurations of Fe and Ni ? (They both have 26 electrons.)
2+
2
2
2
6
6
2
Ans. Fe 1s 2s 2p 3s 3p 4s 3d 6
2
6
2
6
2
2
Ni 1s 2s 2p 3s 3p 4s 3d 8
0
2
6
2
6
2
Ni 2+ 1s 2s 2p 3s 3p 4s 3d 8
The Ni atom has two more 3d electrons; the Ni 2+ ion has lost its 4s electrons. Thus, the Ni 2+ ion has two
more 3d electrons and two fewer 4s electrons than the Fe atom has.
Supplementary Problems
5.51. (a) How many electrons are there in the outermost shell of an atom of phosphorus? (b) How many additional electrons
is it necessary for an atom of phosphorus to share in order to attain an octet configuration? (c) How many additional
electrons is it necessary for an atom of chlorine to share in order to attain an octet configuration? (d) Write the
formula for a compound of phosphorus and chlorine. (e) Draw an electron dot structure showing the arrangement of
electrons in a molecule of the compound.
Cl P Cl
Ans. (a) 5 (It is in periodic group VA.) (b)3(8 − 5 = 3) (c)1(8 − 7 = 1) (d) PCl 3 (e)
Cl
5.52. Write a formula for a binary compound formed between each of the following pairs of elements.
(a) Na, Cl; (b) Mg, I; (c)K,P;(d)K,S;(e) Li, N; ( f ) Al, O; (g) Al, F; (h) Mg, N; (i) P, Cl; ( j) Cl, Mg; (k) O, Mg;
(l) Si, Cl; and (m)S,F.
Ans. (a) NaCl (b) MgI 2 (c)K 3 P(d)K 2 S(e)Li 3 N( f )Al 2 O 3 (g) AlF 3 (h)Mg 3 N 2 (i) PCl 3
( j) MgCl 2 (The metal ion is written first.) (k) MgO (l) SiCl 4 (m)SF 2 (or SF 4 or SF 6 )
5.53. Which of the following compounds involve covalent bonding? Which involve electron sharing? (a) MgCl 2 ,(b) SCl 2 ,
and (c) (NH 4 ) 2 S.
Ans. SCl 2 and (NH 4 ) 2 S involve covalent bonding and therefore, by definition, electron sharing. (NH 4 ) 2 S also
exhibits ionic bonding. (MgCl 2 is entirely ionic.)
5.54. You can predict the formula of the compound between Na and Cl, but not between Fe and Cl. Explain why.
Ans. Na is a main group element and forms Na only in all of its compounds. Fe is a transition element and forms
+
two different ions: Fe 2+ and Fe .
3+