Guide to Chapter 7. Covalent Bonds and Molecular Structure
We will spend three lecture days on this chapter. In this chapter we will learn more about the structure of the
covalent molecules. We will start with a discussion of electronegativity, bond polarity, dipoles, ion electron
configuration and relative size, lattice energy, covalent bond energies, and Lewis dot structures. Once we are
able to sketch Lewis dot structures for molecules, we will take up some exceptions to the octet rule, the concept
of resonance, formal charge, and the shape of molecules. Finally, we will cover expanded octets, hybridization, 
and  bonds.
This is a chapter study guide, given section-by-section. Work problems on separate sheets of paper and keep
them with this guide. When working problems, use plenty of space and when appropriate, show all work.
 Read the introductory paragraph to Chapter 7. Covalent Bonds and Molecular
Structure and Section 7.1 The Covalent Bond
 Read Section 7.2 Strengths of Covalent Bonds.
  Learning Objective 1: Know how to use a bond energy table to estimate the strength of covalent bonds.
 Read Section 7.3 Comparison of Ionic and Covalent Compounds.
  Learning Objective 2: Know the differences in the physical properties between ionic compounds and
molecular compounds (covalent). Know the forces that hold ionic compounds together. Know the forces
that hold molecular compounds together.
 Read Section 7.4 Polar-Covalent Bonds: Electronegativity.
  Learning Objective 3: Know the meaning of the term electronegativity.
  Learning Objective 4: Know the periodic trend in electronegativity of the elements. Given a group of
elements, use the periodic table to predict the most/least electronegative element or rank them in order
of increasing electronegativity.
  Learning Objective 5: Be able to predict the polarity of a bond (+ and -) and the "direction" of the
dipole moment for a given bond between two elements.
  Learning Objective 6: Given a species that has covalent bonds, assign a + and a - to all the atoms in
the molecule.
  Learning Objective 7: Given the formula of a simple compound determine if it is mostly ionic or mostly
covalent.
 Do Problems 1 - 3 at the end of the section.
 Do the following end-of-chapter problems: 38. 40, 42, 44
 Problem Club Question A. Using only a periodic table, circle the most electronegative member from each
group: Answers in blue
(a) P
As
Sb
(b) Ge As
Se
(c) Ga Si
N
(d) F
(e) S
(f) C
Cl
Cl
Si
Br
Ar
Ge
 Problem Club Question B. Using only a periodic table whenever possible, circle the most polar bond from
each group. (In some cases, you may need to use a table from the text.): Answers in blue
(a) C-N or C-O
(d) C-H or Si-H (almost the same! I had to look up exact EN values)
(b) N-F or P-F
(e) H-H or F-F (neither)
(c) F-Cl or F-Br
(f) C-O or C-S
 Problem Club Question C. When the electronegativity difference between the two atoms is very small or
zero, the resulting bond is called a [non-polar covalent] bond, since the bonding electrons are essentially
equally shared.
(a) ionic
(b) polar covalent
(c) non-polar covalent
(d) metallic
Dr. Mattson, General Chemistry, Chm 203, Guide to Chapter 7. Covalent Bonds & Molecular Structure 1
 Problem Club Question D. Which of these bonds is the most polar? C-N
C-O
O-F
N-F
C-F
 Read Section 7.5 Electron Dot Structures.
  Learning Objective 8: Determine the number of valence electrons in an atom or ion.
  Learning Objective 9: Given the formula of a simple covalent species (a molecule or polyatomic ion),
draw its Lewis structure. The Lewis structure MUST clearly show all bonding pairs and lone or
nonbonding pairs of electrons. Use the guidelines from class notes and text.
  Learning Objective 10: Use the Lewis structure to determine the ABE formula for a given molecule.
  Learning Objective 11: Use the Lewis structure to determine the bond order (single, double or triple).
  Learning Objective 12: Given examples of covalent species, rank the length and strength of the bonds.
The structure of ammonia surprised early scientists.
  Learning Objective 13: Determine by inspection if a structure is paramagnetic or diamagnetic.
 Do Problems 4 and 5 at the end of the section.
 Do the following end-of-chapter problems: 48, 56
 Problem Club Question E. Draw the Lewis dot structures for the following molecules and polyatomic ions.
In some cases, you will have to predict the formula of the compound. (a) NF3; (b) OCl2; (c) TeH2; (d)
NH4+; (e) NH2-; (f) SiH?; (g) SeF?; (h) OH3+; (i) CO32Answer: Using the notation that the central atom is designated by “A”, the bonding groups by “B” and
the electron groups by “E”, the answers are: (a) AB3E, (b) AB2E2, (c) AB2E2, (d) AB4, (e) AB2E2, (f)
AB2E, (g) AB2E2, (h) AB3E, and (i) AB3
 Problem Club Question F. Carefully draw the Lewis dot structures of the following molecules and ions: (a)
NO2-; (b) CO2; (c) H2Te; (d) NF3; (e) NH2-; (f) SiO44-; (g) PCl4+; (h) BF3; (i) SCN- (C is central); (j) NO2;
(k) CO 2-; (l) SO -2
3
4
Answer: Using the notation that the central atom is designated by “A”, the bonding groups by “B” and
the electron groups by “E”, the answers are: (a) AB2E, (b) AB2, (c) AB2E2, (d) AB3E, (e) AB2E2, (f) AB4,
(g) AB4, (h) AB3, (i) AB2, (j) AB2E, (k) AB3, and (l) AB4
(i) Which disobey(s) the octet rule? Answer: h and j
(ii) Which has/have one or more lone pairs on the central atom? Answer: a, c, d, e, j
(iii) Which has/have resonance? Answer: a, I, j, k
(iv) Which is/are paramagnetic? Answer: j
(v) Which has/have at least one double or triple bond? Answer: a, b, I, j, k
 Problem Club Question G. In which of the following is the oxygen-oxygen bond predicted to be the:
(a) shortest:
O2
O2-2
O2+2
(b) longest:
O2
O2-2
O2+2
(c) weakest:
O2
O2-2
O2+2
(d) strongest:
O2
O2-2
O2+2
 Read Section 7.6 Electron Dot Structures of Polyatomic Molecules.
  Learning Objective 14: Be able to extend the concepts of Section 7.5 to more complex systems with more
than one central element.
 Do Problems 6 - 11 throughout this section.
 Do the following end-of-chapter problems: 52, 58
 Read Section 7.7 Electron Dot Structures and Resonance.
Dr. Mattson, General Chemistry, Chm 203, Guide to Chapter 7. Covalent Bonds & Molecular Structure 2
  Learning Objective 15: After drawing your Lewis structure, determine if resonance forms are possible
and draw the Lewis structure of each resonance form.
 Do Problems 12 - 14 at the end of the section.
 Do the following end-of-chapter problems: 50, 54
 Problem Club Question H. In which ONE of the following is resonance predicted? XeO2
TeO3
SO3-2
ClO4-
 Problem Club Question I. Which of the structures that you drew in Probem Club Question F has/have
resonance? (a) NO2-; (b) CO2; (c) H2Te; (d) NF3; (e) NH2-; (f) SiO44-; (g) PCl4+; (h) BF3; (i) SCN- (C is
central); (j) NO2; (k) CO32-; (l) SO4-2
 Read Section 7.8 Formal Charges.
  Learning Objective 16: After you have drawn the Lewis structure or you are given a Lewis structure of a
molecule or polyatomic ion, determine the formal charge of each element in the Lewis structure.
  Learning Objective 17: Chemists use formal charges to determine the best Lewis structure of a covalent
species that can have more than one possible Lewis structure. Given an example such as N 2O or OCN, use formal charges to determine the best Lewis structure.
 Do Problems 15 and 16 at the end of the section.
 Do the following end-of-chapter problems: 60, 62, 64
 Problem Club Question J. Nitrous oxide is shown here. The bonding is
nitrogen-nitrogen-oxygen. (a) Sketch the Lewis dot structure and assign
formal charges to your structure. (b) How many  and  bonds are all
together present in nitrous oxide?
Answer: Two resonance forms are important: One features N double-bonded to
N double bonded to O and has formal charges of –1 +1 0, respectively.
Another has N triple bonded to N single bonded to O with FCs of 0, +1 and –1, respectively. (b) Bothe
forms have two  and two  bonds.
 Problem Club Question K. Assign formal charges to each atom in the structures you drew in Probem Club
Question F: (a) NO2-; (b) CO2; (c) H2Te; (d) NF3; (e) NH2-; (f) SiO44-; (g) PCl4+; (h) BF3; (i) SCN- (C is
central); (j) NO2; (k) CO32-; (l) SO4-2
Answer: (a) NO -has two resonance forms — the single bonded O will have FC = -1 and the other two atoms
2
will have FC = 0; (b) CO2 all FC = 0; (c) H2Te all FC = 0; (d) NF3 all FC = 0; (e) NH2-The formal
charges will be 0 for the two Hs and –1 for N; (f) SiO 4-FC = 0 for Si and –1 for each O; (g) PCl +Cls
4
4
have FC = 0 and P has FC = +1; (h) BF3 All FCs = 0 (i) SCN- has two resonance forms — one of them
features S single bonded to C triple bonded to N with FCs of –1, 0, and 0 for S, C, and N, respectively.
The other, better structure has S double-bonded to C which is double-bonded to N with FC = 0 for S and
C and –1 for N; (j) NO2 Two resonance forms are important: Both feature N double-bonded to one O
and single-bonded to the other O — the single bonded O has FC = -1, the double-bonded O has FC = 0
and N has formal charges of +1; (k) CO 2- Three resonance forms are important: Each features C
3
double-bonded to one O and single-bonded to the other two Os — the single bonded O has FC = -1, the
double-bonded O has FC = 0 and C has formal charges of 0; (l) SO4-2 If one does not expand S’s octet,
there will be only one structure which features all Os singly-bonded to S with FC = -1 for each O and +2
for S.
 Read Section 7.9 Molecular Shapes: The VSEPR Model.
Dr. Mattson, General Chemistry, Chm 203, Guide to Chapter 7. Covalent Bonds & Molecular Structure 3
  Learning Objective 18: For a covalent species, draw its Lewis structure first, then use VSEPR theory to
predict its molecular geometry (tetrahedral, bent, etc.), draw the shape, determine the bond angles,
count the number of bonding pairs and lone pairs of electrons.
 Do Problems 17 - 19 at the end of the section.
 Do the following end-of-chapter problems: 32, 34, 36, 66, 68, 70, 72 (a-c), 74, 76, 78
 Problem Club Question L. Give its ABE VSEPR designation and name each geometric shape for each
structure in Problem Club Question F, above: (a) NO2-; (b) CO2; (c) H2Te; (d) NF3; (e) NH2-; (f) SiO44-;
(g) PCl4+; (h) BF3; (i) SCN- (C is central); (j) NO2; (k) CO32-; (l) SO4-2
Answer: (a) AB2E; (b) AB2; (c) AB2E2; (d) AB3E; (e) AB2E2; (f) AB4; (g) AB4; (h) AB3; (i) AB2; (j) AB2E; (k)
AB3; (l) AB4
 Problem Club Question M. What structure (bent, tetrahedral, etc.) is shown here?
Give the name and predicted angles.
Answer: see-saw with angles of approximately 120, 90 and 180 degrees (some
distortion towards smaller angles occurs because of the E group in the equatorial
position.
 Problem Club Question N. Match each compound or ion with the correct ABE formula and structural
name.
J
K
I
A
F
E
H
C
B
D
G
NO2
SF6
SCl2
NH3
SO3
SO2
ClF3
BeF5
SO4-2
N2
CS2
A. AB3E structure
B. tetrahedral
C. square pyramid
D. bond order 3
E. sp2 and resonance
F. trigonal plane
G. AB2
H. T-shaped
I. bent, <109o angle
J. paramagnetic
K. octahedral
 Problem Club Question O. (ACS-Style) Answer: D
 Problem Club Question P. (ACS-Style) Answer: B
 Problem Club Question Q. (ACS-Style) Answer: C
 Problem Club Question R. (ACS-Style) Answer: C
 Problem Club Question S. (ACS-Style) Answer: D
These three sections all go together:
 Read Section 7.10 Valence Bond Theory.
Dr. Mattson, General Chemistry, Chm 203, Guide to Chapter 7. Covalent Bonds & Molecular Structure 4
 Read Section 7.11 Hybridization and sp 3 Hybrid Orbitals.
 Read Section 7.12 Other Kinds of Hybrid Orbitals.
  Learning Objective 19: From the Lewis structure, determine the hybridization for each atom in the
molecule.
  Learning Objective 20: Be able to sketch the orbital diagram and energy diagram for the valence
electrons in an hybridized molecule/ion.
  Learning Objective 21: Show (using a sketch) how the hybridized orbitals of two elements overlap to
form  and  bonds. Clearly show (using arrows) the shared electrons in the bond.
  Learning Objective 22: For a given Lewis structure of a molecule, count the number of  and  bonds.
 Do Problems 20 - 25 throughout these sections.
 Do the following end-of-chapter problems: 84, 86, 88, 90
 Problem Club Question T.
; (i)
Answer: (a) AB E; (b) AB E; (c) AB ; (d) AB E ; (e) AB E3; (f) AB E; (g) AB
; (i) AB ; (j)
AB E; (k) AB ; (l) AB
Answer: c and l
(ii) Which have five structural groups (lone pairs, bonding pairs, and/or unpaired electrons) on the
central atom? Give their structural names. Answer: b, d, e, l
(iii) Which have six structural groups (lone pairs, bonding pairs, and/or unpaired electrons) on the
central atom? Give their structural names. Answer: f, g
(iv)



Answer: a (2 
); h (3 
); i (2 
); j (2 
); k (3

)
(v) Which have sp2 hybridization? Answer: a, h, j, k
(vi) Which feature 120o and 90o angles? Answer: b, d, e, l
(vii) Which have d2sp3 hybridization? Answer: c, f, g
(viii) Which have formal charges other than zero on one or more atoms within the molecule/ion? Answer:
a, e, f, g, h, i, j, k
 Problem Club Question U. (ACS-Style) Answer: D
 Problem Club Question V. (ACS-Style) Answer: A
Skip Sections 7.13 – 7.15.
General Questions:
 Problem Club Question X. In the molecule shown here, ethane, the dark spheres are carbon and the light
spheres are hydrogen.
(a) What is the formula for ethane?
(b) What is the hybridization for each carbon?
(c) What bond angles are present?
(d) What ABE formula describes each carbon?
(e) What is the C-C bond order?
(f and g) Sketch the Lewis dot structure using dots and lines for ethane (two
drawings).
Answer: (a) C H6; (b) sp3; (c) 109o; (d) AB4; (e) 1
Dr. Mattson, General Chemistry, Chm 203, Guide to Chapter 7. Covalent Bonds & Molecular Structure 5