Culver City H.S.  Chemistry Honors
Name _________________________________
Period ___ Date ___/___/___
9  Covalent Bonding
LEWIS STRUCTURES
1. A bond forms when two orbitals ____________
allowing electrons to be close to two nuclei at
the same time. When two atoms bond, they
overlap electrons in their __________ orbitals.
2. As two atoms approach each other, the potential
energy ____________ because of the electronproton attractions. The potential energy
__________ because of electron-electron and
proton-proton repulsions. See Figure 9-1 on
p.242.
3. When a covalent bond forms, two ______ __________ orbitals overlap. Hydrogen only
uses one orbital, the _____ orbital.
Draw and label oxygen’s valence orbitals:
Oxygen:
Consider the two H atoms and the O atom in a
water molecule.
How many bonds are shown? _____
For each bond, the hydrogen orbital uses its
____ orbital. The oxygen atom uses its two
half-filled ____ orbitals to overlap each of the
hydrogen’s half-filled orbitals.
4. Draw the Lewis dot symbol for H2O.
The oxygen atom is surrounded by ____ e-‘s.
5. The Lewis symbol for O can be drawn two
ways, so the Lewis symbol for H2O can be
drawn two ways. Draw them:
Which one is correct? ________________
(Consider the picture of water.)
6. Not all atoms follow the octet rule.
Elements ___ through ___ are too small.
Families ___, ___, and ___ also do not follow
the octet rule when forming covalent bonds.
However, these families are USUALLY
involved in ionic bonds.
Some atoms have MORE than an octet, too, this
is called the “extended valence shell”.
7. Each of the diatomic elements involves a
covalent bond.
Draw the Lewis symbol for each one.
Which one does not follow the octet rule? ___
Diatomic
Lewis
Molecule
Symbol
H2
H H
N2
N N
O2
O O
F2
F F
Cl2
Cl Cl
Br2
Br Br
I2
I I
8. The Lewis Structure of a molecule shows how
the valence electrons are arranged among the
atoms in the molecule.
Steps for Writing Lewis Structures:
a. Sum the valence electrons from all the
atoms. Do not worry about keeping track of
which electrons come from which atoms. It
is the total number of electrons that is
important.
b. Use a pair of electrons to form a bond
between each pair of bound atoms.
c. Arrange the remaining electrons to satisfy
the duet rule for hydrogen and the octet rule
for the second-row elements.
Example: Give the Lewis structure for each of the
following:
a. HF
9. The rules we have used for Lewis structures
apply to most molecules, but there are
exceptions.
Incomplete Octet:
Boron, for example, tend to form compounds in
which the boron atom as fewer than 8 electrons.
BF3
Expanded Octet:
Some atoms exceed the octet rule. This behavior
is observed only for those elements in Period 3
of the periodic table and beyond.
SF6
b. N2
c. NH3
d. CH4
e. CF4
f. NO+
Comments about the Octet Rule:
1. The second-row elements C,N,O, and F
should always be assumed to obey the octet
rule.
2. The second-row elements B and Be often
have fewer than 8 electrons around them in
their compounds. These electron-deficient
compounds are very reactive.
3. The second-row elements never exceed the
octet rule, since their valence orbitals (2s
and 2p) can accommodate only 8 electrons.
4. Third-row and heavier elements often satisfy
the octet rule but can exceed the octet rule
by using their empty valence d orbitals.
5. When writing the Lewis structure for a
molecule, satisfy the octet rule for the atoms
first. If electrons remain after the octet rule
has been satisfied, then place them on the
elements having available d orbitals
(elements in Period 3 or beyond).