Gateway 125,126, 130
Fall 2005
Week 4, Section p1
Week 4, Section 1: 9/28: Types of Bonds
1) Polar
2) Ionic
3) Metallic
4) Bonding Triangle
Reading: 8.7 p- 354-357; 9.5 p405-409; 3.2 p 81-82; 3.5 p 88-99
New Group Formation
Introduce yourselves to the group. Tell everyone three things about yourself (such as favorite
place to travel, what you did last summer, your favorite movie, your favorite meal to fix, what
you like to do on the weekends, what you aim to be when you “grow up,” etc.) Exchange
information such as e-mail/phone/address.
Then share responses to the following questions:
1. What do you perceive to be your responsibilities to the group (list these on the board or
on paper)
2. What are the responsibilities the group has to each member
3. Describe the advantages of working in a group or as a team
4. Describe the disadvantages of working in a group or as a team
Draft a Group Covenant based on your discussion of the questions above which outlines each
group members' responsibilities to the group and the group responsibilities to each member. (3-5
sentences.) Write/print out a copy of the covenant and have every group member sign it and give
a copy to your GSI. You may want to keep a copy for yourselves.
Group assignments for today: A Recorder; B Skeptic; C Leader
Gateway 125,126, 130
Fall 2005
Week 4, Section p2
1) Bonds, Polar Bonds (In conjunction with Powerpoint whole section
discussion/demonstration)
For a molecule to be polar it must:
a) have at least 1 polar bond or 1 lone pair and
b) polar bonds or LP must be arranged in space so that the dipoles do not cancel out
Fill in each box with:
# valence electrons
Lewis structure
Molecular structure
Dipole arrow
HCl
CO2
NH3
SF4
C2H2
BF3
CHCl3
ICl3
XeF2
XeF4
SF6
BrF5
Gateway 125,126, 130
Fall 2005
Week 4, Section p3
2) Bonds, Ionic Bonds
Does the difference in electronegativity between atoms ever get so large that the more
electronegative atom takes the electrons away from the less electronegative atom?
The result is an ionic bond: the atoms involved undergo a transfer of one (or more electrons) to
produce two charged species: a positive ion (cation) and a negative ion (anion). Remember
from studying periodic trends, you can predict which elements form cations and which form
anions and what their charges are.
There are also many polyatomic ions. They have covalent bonds between the atoms of the ion,
but form ionic complexes with other ions. For example NaNO3 has an ionic bond between Na+
and NO3-, and covalent bonding between nitrogen and oxygen.
Table 1: Polyatomic cations and anions
Cation
Anions
+
NH4
Ammonium
OHhydroxide
+
H3O
Hydronium
CNcyanide
-2
CO3
carbonate
CH3COO- acetate
SO4-2
sulfate
-2
SO3
sulfite
NO3nitrate
NO2
nitrite
PO4-2
MnO4-2
CrO4-2
Cr2O7ClO4ClO3ClO2ClO-
phosphate
permanganate
chromate
dichromate
perchlorate
chlorate
chlorite
hypochlorite
You should commit the names, molecular formula, and charges of the ions in
Table1 above to memory by next week!
Question: If ionic bonds are created when atoms undergo a transfer of electrons to form cations
and anions, how do they form bonds?
Data/Fact Gathering: There is a force, described by Coulomb’s Law which exists between
charges.
The force is attractive between positive charges and negative charges and repulsive between
multiple positive charges, and multiple negative charges. The magnitude of the forces increases
as the magnitude of the charges increases. The force decreases with the distance between the
charges.
q1, q2 -are the magnitudes of the two charges
r
-is the distance between them
k
-is a constant
Gateway 125,126, 130
Fall 2005
Week 4, Section p4
A bond distance is set when the electron clouds of the atoms overlap and the attractive forces
between the oppositely charged ions is balanced by the repulsive forces between the two nuclei
and the electrons.
Ions form an ordered solid as shown in Figure 1 so that symmetry causes the attractive and
repulsive forces to balance each other and the energy to be minimized.
Figure 1: a) A model of the distribution of charges in an ionic compound; b) Ionic
compound upon deformation
a)
b)
1) Ionic compounds tend to have very high melting point. Why is this?
2) Ionic materials are generally brittle, that is they break suddenly with little deformation before
breaking. Why is this?
Gateway 125,126, 130
Fall 2005
Week 4, Section p5
3) Bonds, Metallic Bonds
Metals are not modeled like covalent or ionic bonds. In metals none of the atoms exert a strong
pull on the electron, the atoms become positive ion cores surrounded by a sea of electrons. The
electrons act like a glue holding the ions together. These ions still create a lattice structure.
Figure 2: a) Model for metallic bonding; b) metal after deformation
a)
b)
Metals are very good conductors because the free electrons can move through a circuit causing a
current. When a metal is deformed, the metallic crystal structure is able to accommodate greater
deformation than an ionic crystal structure. This property of metals is called ductility.
Gateway 125,126, 130
Fall 2005
Week 4, Section p6
Question: So how do you know whether a bond is covalent, ionic, or metallic?
Data/Fact Gathering
Table 2: Electronegativity, EN parameters and melting points for selected compounds1
EN
EN
___
Melting
Type of
Compound
EN
1st atom
2nd atom
EN
point (oC)
bonding
CsF(s)
0.66
4.19
2.42
3.53
682
ionic
NaCl(s)
0.87
2.87
1.87
2.00
801
ionic
NaI(s)
0.87
2.36
1.62
1.49
661
ionic
Cs(s)
0.66
Na(s)
0.87
CuZn(s; brass) 1.8
0.66
0.87
1.8
0.66
0.87
1.7
0
0
0.2
28
98
932
metallic
metallic
metallic
F2(g)
O2(g)
HI(g)
C(s; diamond)
4.19
3.61
2.36
2.54
4.19
3.61
2.33
2.54
0
0
0.06
0
-220
-218
-51
>3000
covalent
covalent
covalent
covalent
4.19
3.61
2.30
2.54
CH4(g)
2.54
2.30
-182
GaAs(s)
1.76
2.21
1238
Si(s)
1.92
1.92
1.92
0
1410
___
EN is the average electronegativity of the two elements
EN is the absolute difference in electronegativity between the two elements
___
3) Based on the data in Table 2, what combination of EN and EN values leads to metallic
bonding?
___
4) Based on the data in Table 2, what combination of EN and EN values leads to ionic
bonding?
___
5) Based on the data in Table 2, what combination of EN and EN values leads to covalent
bonding?
1
Moog, R. S.; Farrell, J. J. “Chemistry A Guided Inquiry” 2nd edition John Wiley & Sons 2002, p 131-135.
Gateway 125,126, 130
Fall 2005
Week 4, Section p7
___
6) Fill in the EN and the EN values for methane (CH4) in Table 1. Classify the C-H bonds in
methane as metallic, ionic, or covalent bonding? Explain.
___
7) Fill in the EN and the EN values for GaAs in Table 1. Is it possible to classify GaAs as
metallic, ionic, or covalent bonding? Explain.
Model 1: Bond-type Triangle
Many compounds have properties that are intermediate between the three bond types. Si, for
example is known as a semiconductor; a compound with properties which are intermediate
between metallic and covalent.
The bond-type triangle is a model that enables one to predict the properties of a compound
based on the electronegativities of the elements that comprise the compound. The data for CsF,
F2, and Cs from Table 1 have been used to generate three points at the corners of the bond-type
triangle shown in Figure 3.
Figure 3: Bond-type Triangle
4
CsF
3.5
3
EN
2.5
A
2
1.5
1
C
0.5
B
0
0
Cs
0.5
1
1.5
SM
2
F2
2.5
[average EN]
3
3.5
4
4.5
Gateway 125,126, 130
Fall 2005
Week 4, Section p8
8) Place points on the chart for sodium chloride (ionic bonding), sodium (a metal), hydrogen
iodide (covalent bonding), and Si (a semiconductor.)
The bond-type triangle can be divided into regions which indicate the predominant type of
bonding present in compounds. The dividing lines between regions are not absolute, but they
give a general idea of the boundaries between different types of bonding.
9) Associate the regions (A, B, C) with bond types (metallic, covalent, ionic). The “SM” region
is sometimes called semimetals.
A
B
C
10) Quartz, SiO2 is a very high melting, hard solid. Place a point for SiO2 on the bond-type
triangle. What type of bonding would you predict to be predominant in quartz?
11) For each of the following compounds, place a point on the bond-type triangle. Classify each
compound as metallic, covalent, ionic, semimetal.
a) CO2
b) NH3
c) BaO
d) SO2
e) AlSb
f) GaAs
g) CdLi
h) BaBr2
i) ZnO
j) NaH
12) Give the type of bonding in each of the following: CO3-2; BaCO3(s); NaClO4(s)