1. #13 p. 229 in the book: What electron configurations
do atoms usually achieve by sharing electrons to form
covalent bonds?
In forming covalent bonds, electron sharing usually occurs so that
atoms attain the electron configurations of noble gases.
symbol
electron configuration
helium He
1s2
neon Ne
[He]2s22p6
argon Ar
[Ne]3s23p6
krypton Kr
[Ar]3d104s24p6
xenon Xe
[Kr]4d105s25p6
radon Rn
[Xe]4f145d106s26p6
The s and p orbitals
are full (8 electrons)

2. #14 How is an electron dot structure used
to represent a covalent bond?
An electron dot structure such as H:H (seen below)
represents the shared pair of electrons
of the covalent bond by two dots
Please see the on-line textbook Chapter 8 section 2
simulation 6 CHEM ASAP! “simulate the covalent bonding between molecules”

4. #15 When are two atoms likely to form
a double bond between them? A triple bond?
Atoms form double or triple covalent bonds if
they can attain a noble gas structure by sharing
two pairs or three pairs of electrons.
Oxygen is
an example
of two atoms
joining and
sharing two
pairs of elect-
rons to form
a double bond.

5. Nitrogen is an example
of two atoms joining and
sharing three pairs of elect-
rons to form a triple bond.

6. #16 How is a coordinate covalent bond different
from other covalent bonds?
In most cova-
lent bonds each
atom contributes
one electron to
the bond. In a
coordinate coval-
ent bond both
electrons are
contributed by
the same atom
Oxygen has to “kick in” two additional electrons to
allow both to have a full octet (eight total) valence
electrons

7. #17 How is the strength of a covalent bond related
to its bond dissociation energy?
A large bond dissociation energy
corresponds to a strong covalent bond.
As you can see in the
table on the right dif-
ferent covalent bonds
have different amounts
of energy needed to
break apart. A large
dissociation energy
(see N triple N) is a
strong bond. A low
(see N-O) is a weak
bond.

8. #18 Draw the electron dot resonance structures
for ozone and explain how they describe its
bonding.
When you have two equally valid options for dot structure
as seen above you have RESONANCE.
Click here to see a movie about how ozone is formed in the upper atmosphere
and its importance in shielding the earth from Ultraviolet radiation
Click here to see a movie about how ozone is destroyed by CFC’s

9. O N O #19 List three ways in which the octet rule can sometimes
fail to be obeyed.
The octet rule cannot be satisfied in molecules:
1. whose total number of valence electrons is an odd number.
2. There are also molecules in which an atom has FEWER THAN 8 valence
electrons,
3. Molecules with MORE than a complete octet of valence electrons. ● ●● ●● ●
Nitrogen has
only 7 valence
electrons ●
O N O ● ● ● ● ● ●
1. Nitrogen
as an ODD
number (5)
of valence
electrons
and thus
sometimes
does not
obey the octet
rule ● ● ● ●

10. #19 continued
2. The boron in BF3 has a deficiency of valence electrons (only 6 total) so it doesn’t obey the octet rule F F B
3. In the case of PCl5 and SF6 the P and the S have MORE THAN the octet (P
has 10 and S has 12) F

11. #20 What kinds of information does a structural
formula reveal about the compound it represents?
It reveals the way the atoms are bonded together:
ie; single bonds, double bonds, triple bonds, and bond angles, unshared pairs, etc.

12. H2S S H H #21 Draw electron dot structures for the following
molecules which have onlysingle covalent bonds.
H2S S H H

13. H P H H
PH3

14. ClF Cl F Cl F

15. The hydrogen bond is stronger due to its greater bond dissociation
# 22. Use the bond dissociation energies of
H2 (435 kJ/mole) and of a typical carbon-
carbon bond (347kJ/mole) to decide which
bond is stronger. Explain your reasoning.
The hydrogen
bond is stronger
due to its greater
bond dissociation
energy (the
amount of energy
needed to break
it.)