CHEMISTRY 11 AP – DESCRIBING CHEMICAL BONDING WORKSHEET
1) Identify the following compounds as either ionic (I) or covalent (C):
(a) MgO
I
(f) PBr5
C
(k) NH4NO2
(b) KrF2
C
(g) KMnO4
I
(l) C3S2
(c) WF6
I
(h) NH4ClO2
I
(m) C6H12O6
(d) CuSO4
I
(i) Al2S3
I
(n) N2O
(e) CH3OH
C
(j) Na2SO3
I
(o) Co(ClO3)2
I
C
C
C
I
2) What is an ionic crystal lattice and how does it explain the high melting points of ionic compounds?
An ionic crystal lattice is the three-dimensional symmetrical arrangement of cations and anions in a
solid ionic crystal. The vast number of interionic forces present in such a crystal must be overcome
to melt and ionic compound and this explains the high melting points of such compounds.
3) Mg2+ and Na+ have roughly the same ionic radius. O2- and F- have roughly the same ionic radius.
Which substance should have a higher melting temperature: NaF or MgO? Why?
Although the ions are about the same size, there is more charge on both Mg2+ and O2-. Recall that
the greater the charge, the greater the force of attraction. The increased attraction between Mg2+ and
O2- requires a greater energy to separate the ions and therefore a higher melting point. This is
confirmed by the fact that the melting temperatures of MgO and NaF are 285.2°C and 993°C
respectively.
4) Which member of each of the following pairs would you expect to have the higher melting point?
(a) CaO or RbI
(c) LiF or NaCl
(e) RbI or KCl
(b) BeO or BN
(d) CsCl or BaS
(f) BeO or MgS
The ionic compounds that have smaller ionic radii would have a greater attraction and would
therefore require more energy to separate the ions resulting in a higher melting point. Additionally,
if the ionic compounds shared similar ionic radii, the pair that contains the greater charge would
have a higher melting point for the same reasons provided in the answer to question 3.
5) Identify the attractive forces associated with:
(a) ionic bonds
The attractive forces associated with ionic bonds are the electrostatic forces between the
positively charged cations and the negatively charged anions.
(b) covalent bonds
The attractive forces associated with covalent bonds are the electrostatic forces between
negatively charged electrons and adjacent positively charged nuclei.
6) Predict the formula of the compound formed by bonding together the following:
(a) P and Cl
PCl3
(e) H and Se
H2Se
(i) C and B
B4C3
(b) B and O
B2O3
(f) F and O
F2 O
(j) C and Cl
CCl4
(c) C and S
CS2
(g) O and H
H2 O
(k) Si and P
Si3P4
(d) O and P
P2 O3
(h) N and I
NI3
(l) S and Si
SiS2
7) Consider the ΔEN values and pair up the elements Al, Cl, N and Na to write the formula for the
types of compounds identified below. Justify each choice by showing the appropriate ΔEN value
next to each formula.
(a) A compound with an ionic bond
NaCl (ΔEN = 2.1)
(b) A compound with a polar covalent bond
AlN (ΔEN = 1.5)
(c) A compound with a non-polar covalent bond
NCl3 (ΔEN = 0)
8) Calculate the ΔEN values for the bonds in the following compounds. Then arrange the compounds
in order from those containing bonds in which the electrons are shared most equally to those in
which the electrons are shared most unequally.
(a) H2O
ΔEN = 1.4
(b) PCl3
ΔEN = 0.9
(c) Cl2
ΔEN = 0
(d) SiO2
ΔEN = 1.7
(e) AlN
ΔEN = 1.5
Compounds in order of most equal to most unequal electron sharing: Cl2, PCl3, H2O, AlN, SiO2
9) Determine the bond dipole and bond dipole strength for the following molecules:
(a) C ⎯ O
(e) C ⎯ Cl
-7,30
0.5
¥
2.5
C-
st
(b) S ⎯ Cl
0
3.5
5
-
C-
st
a
3.0
5
(f) O ⎯ H
1.4
05
25g
st
2.5
£
3j5¥H2j+
(c) N ⎯ Br
(g) N ⎯ I
0.5
0.2
3j¥Bgt8
(d) P ⎯ O
2.1
st
N
←
5st
-
2.5
g
(h) C ⎯ N
1.4
-
p
3.0
-
0
0.5
3.5
5
2.5
st
-
C
-
3. 0
N
s
-
10) Many covalent compounds have much lower melting points than ionic compounds. Why does this
not mean that covalent bonds are weaker than ionic bonds?
The melting of molecular covalent compounds does not involve breaking of covalent bonds within
the molecules, but rather overcoming the relatively weak attractive forces between those molecules
in the solid phase.
11) Diamond is a form of pure carbon containing only covalent bonds. It is the hardest substance known
and has a melting point of about 3,550°C. What name do we give to this type of covalent substance?
Suggest a reason for its very high melting point?
Diamond is a type of covalent substance that is known as a network covalent solid. Rather than
consisting of individual molecules as molecular covalent compounds do, these substances are held
together by covalent bonds that extend throughout the entire sample. This means that the
“molecule” is literally as big as the sample itself. To melt such a substance, all of the covalent bonds
within this giant molecule must be broken and this accounts for the very high melting point.
12) Consider the nature of the covalent bonds present in HCl and in N2. Which substance would you
expect to have the higher melting point? Give a reason for your answer.
The bond in HCl is a polar covalent bond (ΔEN = 0.9) whereas the bond in N2 must be pure covalent
(ΔEN = 0). This means that electron density in the HCl molecule is concentrated on the chlorine
side of the molecule making that end of the molecule somewhat negative and the hydrogen end of
the molecule somewhat positive. We might expect therefore, that HCl molecules would attract each
other more strongly than N2 molecules where the electron density is evenly distributed throughout
the molecule. The melting point of HCl is –114.2°C and the melting point of N2 is –210°C.