Gillespie, Chapter 3
Solutions to Homework Problems
6. Part Element Category Group Type
a Ar, argon Main Group VIII nonmetal
b Rb, rubidium Main Group I metal
c V, vanadium Transition - metal
d Br, bromine Main Group VII nonmetal
e Ba, barium Main Group II metal
f Fe, iron Transition - metal
g Au, gold Transition - metal
13. (a) Li (Group I) has a valence of 1 and S (Group VI) a valence of 2,
so the product is Li2S
2 Li(s) + S(s) -----> Li2S(s) lithium sulfide
(b) Mg (Group II) has valence 2 and H (Group I) has valence 1,
so the product is MgH
2
Mg(s) + H (g) -----> MgH (s) magnesium hydride
2 2
(c) Al (Group III) has valence 3 and Br (Group VII) has valence 1,
so the product is AlBr3
2 Al(s) + 3 Br2(l) -----> 2 AlBr3(s) aluminum bromide
(d) Sr (Group II) has valence 2 and Br has valence 1, so the
product is SrBr2
Sr(s) + Br2(l) -----> SrBr2(s) strontium bromide
15. We need to know the valences for part (a) and (b), which for elements
in Groups I - IV are the same as the Group number while for elements
in Groups V - VIII are 8 minus the Group number.
ELEMENT Mg K Br P Si Al S C F
GROUP II I VII V IV III VI IV VII
PERIOD 3 4 4 3 3 3 3 2 2
VALENCE 2 1 1 3 4 3 2 4 1
(a) Fluorides: Mg2F KF BrF PF3 SiF4 AlF3 SF2 CF4
(b) Sulfides: MgS K2S Br2S P2S3 SiS2 Al2S3 S2 CS2
22. Part Atom At.# Period Group Shell Core
(Z) Structure Charge
a C 6 2 IV 2,4 +6-2 = +4
b Mg 12 3 II 2,8,2 +12-10 = +2
c Mg2+ 12 3 II 2,8,0 +12-2 = +10
d Si 14 3 IV 2,8,4 +14-10= +4
e O 8 2 VI 2,6 +8-2 = +6
f O2- 8 2 VI 2,8 +8-2 = +6
g S2- 16 3 VI 2,8,8 +16-10 = +6
h Br 35 4 VII 2,8,18,7 +35-28 = +7
30. (a) Ca (Group II) loses 2 e- to give Ca2+ while I (Group VII) gains
one e- to become I-
.
.Ca. -----> Ca2+ + 2 e- and :I: + e- -----> I-
¨
..
then Ca2+ + 2 I- -----> CaI2 ionic Ca2+[:I:-]2
¨
.
(b) .Ca. -----> Ca2+ + 2 e- and .O: + 2 e- -----> O2-
¨
..
then Ca2+ + O2- -----> CaO ionic Ca2+:O:2-
¨
. .
(c) .Al. -----> Al3+ + 3 e- and .S: + 2 e- -----> S2-
¨
..
then 2 Al3+ + 3 S2- -----> Al2S3 ionic [Al3+]2[:S:2-]3
¨
.
(d) .Ca. -----> Ca2+ + 2 e- and :Br: + e- -----> Br-
¨
..
then Ca2+ + 2 Br- -----> CaBr2 ionic Ca2+[:Br:-]2
¨
.
(e) Rb. -----> Rb+ + e- and :Se. + 2 e- -----> Se2-
¨
..
then 2 Rb+ + S2- -----> Rb2S ionic [Rb+]2:S:2-
¨
33. (a) A single covalent bond consists of a pair of electrons shared
between two atoms; the mutual attraction of each atom for the same
electron pair bonds them together,
.. .. .. ..
as in the F2 molecule :F:F: or :F-F:
¨ ¨ ¨ ¨
(b) A double covalent bond consists of two pairs of electrons shared
between two atoms; the mutual attraction of each atom for the same
electron pair bonds them together,
.. .. .. ..
as in the O2 molecule :O::O: or :O=O:
¨ ¨ ¨ ¨
(c) A TRIPLE covalent bond consists of three pairs of electrons shared
between two atoms; the mutual attraction of each atom for the same
electron pair bonds them together,
as in the N2 molecule :N:::N: or :N{3 horizontals}N:
_
Yes, I agree, we need more symbols because :N=N: looks not
like a triple bond by rather a double bond with a negative
charge...not at all intended. :N#N: ?
(d) A shared (bonding) electron pair is a pair of electrons shared
between two atoms that bonds them together; e.g., any of the
electrons shared in bonding of F2, O2, or N2.
(e) An UNshared (nonbonding) electron pair is any pair of electrons
in the valence shell of an atom that does NOT participate in
chemical bonding, that is, is not shared with another atom; for
example, any of the three electron pairs associated with each
F atom in the F2 molecule that don't partipate in the F-F bond.
38. (a) The ELECTRONEGATIVITY of an atom is its relative power of attraction
for the electron pair OF A COVALENT BOND. The attraction results
from the electrostatic attraction of the nucleus of an atom for a
pair of electrons in its valence shell, which is proportional to
the magnitudes of the core charge and the electron charge, and
inversely proportional to the square of their distance apart
Coulomb's Law, electrostatic force proportional to Q1Q2/r²
So the electronegativity of an atom will depend primarily on
(i) its CORE CHARGE, and (ii) the distance of the valence shell
electrons from the nucleus.
(b) CORE CHARGE increases ACROSS ANY PERIOD from left to right from
+1 (Group I) to +8 (Group VIII), and the valence electrons are in
the same shell, n, so their distances from the nucleus are about
the same. Thus, electronegatity is expected to increase from
left to right across any period, as is observed. In ANY GROUP,
the core charge remains the same (equal to the group number) but
the distance of the valence shell fro the nucleus progressively
increases as the number of filled inner shells of electrons
increases. Thus, the Coulombic force of attraction for the outer
valence electrons decreases, and electronegativity is expected to
decrease, in descending any Group, as is observed.
41. Compound Bond Type Explanation
(c) O2 Covalent bond between IDENTICAL atoms
(d) SO2 (e) ClO2 (f) NO Polar Covalent bonds between NONMETALS
of different electronegativities
(a) Li2O (b) MgO Ionic METAL-NONMETAL bonds
50. Molecule Lewis Structure Type Shape
..
(a) H2S H - S - H AX2E2 bent
¨
.. .. ..
(b) NF3 :F - N - F: AX3E1 triangular pyramidal
¨ \ ¨
:F:
¨
(c) BeH2 H - Be - H AX2 linear
H
/
(d) GeH4 H - Ge - H AX4 tetrahedral
\
H
51. (a) Four single bond domains each occupy 1/4 of the volume in the
valence shell of a central atom to give a TETRAHEDRAL arrangement
of electron pair domains.
(b) Three single bond domains and a lone pair domain also adopt
a TETRAHEDRAL arrangement.
(c) Two single bond domains and two lone pair domains do likewise.
(d) One single bond domain and three lone pair domains do likewise.
(e) One double and two single bond domains arrange themselves in the
(AX3) TRIANGULAR PLANAR bonding but the double domain is larger
than either single bond domain.
(f) Two double bond domains each take up half of the volume of the
valence shell of the central atom and have a LINEAR arrangement.
(g) A single bond domain and a triple bond domain are also LINEAR.
(h) A triple bond domain and a lone electron pair are also LINEAR.
53. Molecule Lewis Structure Type Shape
.. ..
BeCl2 :Cl - Be - Cl: AX2 Linear Cl - Be - Cl
¨ ¨
..
:Cl: Cl
| |
BCl3 B AX3 Planar triangular B
/ \ / \
:Cl: :Cl: Cl Cl
¨ ¨
..
:Cl: Cl Cl
.. | .. \ /
CCl4 :Cl - C - Cl: AX4 Tetrahedral C
¨ | ¨ / \
:Cl: Cl Cl
¨
.. .. .. N
NCl3 :Cl - N - Cl: AX3E1 Pyramidal triangular / | \
¨ \ ¨ Cl Cl Cl
:Cl:
¨
.. .. .. O
OCl2 :Cl - O - Cl: AX2E2 Bent (angular) / \
¨ ¨ ¨ Cl Cl
.. ..
FCl :Cl - F: AX1E3 Linear F - Cl
¨ ¨
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Last modified 12 June 1996.