Homework, Chapter 11 (paired exercises, p. 257): 1, 3, 13, 29, 37
1.
3.
13.
29.
Which one in each pair has the largest radius? Explain.
a) Ca atom or Ca ion: Ca, because in Ca2+, nucleus holds remaining electrons
more strongly and the ion contracts.
b) Cl atom or Cl ion: Cl-, nucleus charge is too small to hold extra electron.
c) Mg ion or Al ion: Mg2+ > Al3+, see explanation (a)
d) Na atom or Si atom: Na atom, radius increases right to left in a period.
e) K ion or Br ion: Br- ion, explanation as in (b).
Using the table of electronegativity values (Table 11.5) indicate which element is
more positive and which is more negative in these compounds:
a. H2O (H is more positive, O more negative); b. NaF (Na more positive); c. NH3
(H more positive); d. PbS (Pb more positive); e. NO (N more positive); f. CH4 (H
more positive)
How many electrons must be gained or lost for the following to achieve a noble
gas structure?
a) A Ca atom: must loose two electrons to achieve [Ar] structure.
b) A S atom: must gain two electrons to achieve [Ar] structure
c) A He atom: must stay as is, already possesses noble gas structure.
Draw Lewis structures for the following:
a) NCl3
.. .. ..
b) H2CO3
..
..
26 e
: Cl – N – Cl :
CO3: 24e H : O – C – O : H
..
| ..
(resonance)
. . || . .
: Cl :
:O:
..
c) C2H6
37.
H H
| |
H–C–C–H
| |
H H
d) NaNO3.
NO3-: 24 e
(resonance)
..
..
:O–N–O:
. . || . .
:O:
Use VSEPR theory to predict the structure of these polyatomic ions:
a) sulfate ion:
32 e, structure as in CH4, tetrahedral
b) chlorate ion:
26 e, structure as in NH3, pyramidal.
c) periodate ion:
32 e, as in CH4 or sulfate ion, tetrahedral
Na+
Homework, Chapter 13 (paired exercises, p. 332): 7, 11, 17, 25.
7.
Name these hydrates:
a. BaBr2 . 2 H2O – Barium bromide dehydrate
b. AlCl3 . 6 H2O – Aluminum chloride hexahydrate
11.
17.
25.
c. FePO4 . 4 H2O – Iron(III) phosphate tetrahydrate
In which of the following substances would you expect to find hydrogen bonding?
(a) C2H6 – no; (b) NH3 – yes; (c) H2O – yes; (d) HI – no; (e) C2H5OH – yes.
Hydrogen bonds exist only between molecules in which hydrogen is bonded
directly to N, O, or F.
How many moles of compound are in 100. g of CoCl2 . 6 H2O?
molar mass: 58.93 + 2(35.45) + 6(18.02) = 237.95.
 1 mol CoCl2 . 6 H2O 
 = 0.420 mol CoCl . 6 H O
100. g x 
2
2

.
 237.95 g CoCl2 6 H2O 
How many joules are needed to change 120. g of water at 20. oC to steam at 100.
o
C?
 4.184 J 
To heat water: Qh = 120. g x  g oC  x (100. – 20) oC = 40.2 kJ


 2.26 kJ 
To vaporize: Qv = 120. g x  g
 = 271.2 kJ


Total heat: Qtot = Qh + Qv = 311 kJ = 3.11 x 105 J