8.2
The Nature of Covalent Bonding
The colors in this map
indicate the concentrations
of ozone in various parts of
Earth’s atmosphere.
Oxygen atoms can join in
pairs to form the oxygen
you breathe and can also
join in groups of three
oxygen atoms to form
ozone.
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The Octet Rule in Covalent Bonding
In covalent bonds, electron sharing
usually occurs so that atoms attain the
electron configurations of noble gases.
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Single Covalent Bonds
Two atoms held together by sharing a pair of
electrons are joined by a single covalent bond.
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Single Covalent Bonds
The halogens form single covalent bonds in their
diatomic molecules. Fluorine is one example.
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Single Covalent Bonds
A pair of valence electrons that is not shared
between atoms is called an unshared pair, also
known as a lone pair or a nonbonding pair.
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Single Covalent Bonds
The hydrogen and oxygen atoms in water attain
noble-gas configurations by sharing electrons.
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Double and Triple Covalent Bonds
A bond that involves two shared pairs of
electrons is a double covalent bond.
Ex O2
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A bond that involves three pairs of shared electrons is called
a triple covalent bond
Ex N2
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Electron Dot Structures
Rules for Drawing Lewis Structures:
1. Count valence electrons for entire
molecule
ex NH3
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2. Draw skeleton structure, connecting all
atoms with single bonds (think
symmetry!!!)
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3. Add unshared pairs of electrons to give
all atoms an octet. (Remember
Hydrogen only gets 2 electrons)
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4. Count total electrons in molecule. If this
number equals number of electrons
from step #1, you’re done. If not, you
must make double or triple bonds.
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Try these:
1 . CO
2. COH2
3. CHCl3
4. HCN
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Double and Triple Covalent Bonds
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Double and Triple Covalent Bonds
Carbon dioxide gas is soluble in water and is
used to carbonate many beverages. A carbon
dioxide molecule has two carbon-oxygen double
bonds.
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Double and Triple Covalent Bonds
Carbon dioxide is an example of a triatomic
molecule.
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Coordinate Covalent Bonds
In carbon monoxide, oxygen has a stable
configuration but the carbon does not.
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Coordinate Covalent Bonds
As shown below, the dilemma is solved if the
oxygen donates one of its unshared pairs of
electrons for bonding.
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Coordinate Covalent Bonds
A polyatomic ion, such as NH4+, is a tightly
bound group of atoms that has a positive or
negative charge and behaves as a unit.
Most plants need nitrogen that is already
combined in a compound to grow.
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Coordinate Covalent Bonds
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8.2
Section Assessment
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Practice Problems for Conceptual Problem 8.2
Section Assessment
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Bond Dissociation Energies
Bond Dissociation Energies
How is the strength of a covalent bond
related to its bond dissociation energy?
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Bond Dissociation Energies
The energy required to break the bond between
two covalently bonded atoms is known as the
bond dissociation energy.
A large bond dissociation energy
corresponds to a strong covalent bond.
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Resonance
Ozone in the upper
atmosphere blocks
harmful ultraviolet
radiation from the sun.
At lower elevations, it
contributes to smog.
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Resonance
The actual bonding of oxygen atoms in
ozone is a hybrid, or mixture, of the
extremes represented by the resonance
forms.
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Resonance
A resonance structure is a structure that
occurs when it is possible to draw two or more
valid electron dot structures that have the same
number of electron pairs for a molecule or ion.
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Exceptions to the Octet Rule
Exceptions to the Octet Rule
There are molecules in which an atom
has fewer, or more, than a complete
octet of valence electrons.
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Exceptions to the Octet Rule
The electron dot structure for PCl5 can be written
so that phosphorus has ten valence electrons.
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8.2 Section Quiz.
Assess students’ understanding
of the concepts in Section 8.2.
Continue to:
-or-
Launch:
Section Quiz
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8.2 Section Quiz.
1. In covalent bonding, atoms attain the
configuration of noble gases by
a. losing electrons.
b. gaining electrons.
c. transferring electrons.
d. sharing electrons.
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8.2 Section Quiz
2. Electron dot diagrams are superior to
molecular formulas in that they
a. show which electrons are shared.
b. indicate the number of each kind of atom in
the molecule.
c. show the arrangement of atoms in the
molecule.
d. are easier to write or draw.
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8.2 Section Quiz
3. Which of the following molecules would
contain a bond formed when atoms share
three pairs of electrons?
a. Se2
b. As2
c. Br2
d. Te2
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