Chemical Bonding
Types of Bonds
Ionic Bonding
Lewis Structures
Covalent Bonding
Resonance Structures
Octet Rule
Polar Molecules
Molecular Geometries
VSEPR
Basic Shapes
3-D Notation
Hybridization (Lab)
Chemical Bonds, Lewis Symbols, and the Octet Rule
• Chemical bond: attractive force holding two or more
atoms together.
• Covalent bond results from sharing electrons between
the atoms. Usually found between nonmetals.
• Ionic bond results from the transfer of electrons from a
metal to a nonmetal.
• Metallic bond: attractive force holding pure metals
together.
Ionic Bonding
Electron Configurations of Ions and their Lewis Structures
Covalent Bonding
Energy Potential Diagram for Covalent Bonds!
Chemical Bonds
Bond Type
Single
Double
Triple
# of e’s
2
4
6
Notation
—
=

Bond order
1
2
3
Bond
strength
Bond length
Increases from Single to Triple
Decreases from Single to Triple
Strengths of Covalent Bonds
Chemical Bonds, Lewis Symbols, and the Octet Rule
Lewis Symbols
Chemical Bonds, Lewis Symbols, and the Octet Rule
The Octet Rule
• All noble gases except He has an s2p6 configuration.
• Octet rule: atoms tend to gain, lose, or share electrons
until they are surrounded by 8 valence electrons (4
electron pairs).
• Caution: there are many exceptions to the octet rule.
Bond Polarity and Electronegativity
Electronegativity
• Electronegativity: The ability of one atoms in a
molecule to attract electrons to itself.
• Pauling set electronegativities on a scale from 0.7 (Cs) to
4.0 (F).
• Electronegativity increases
• across a period and
• down a group.
Figure 8.6: Electronegativities of Elements
Electronegativity
Difference in Electronegativities
0 to 0.5 Nonpolar covalent
0.5 to 1.7 Polar covalent
>1.7 Ionic
Bond Polarity and Electronegativity
Figure 8.7: Electronegativity and Bond Polarity
• There is no sharp distinction between bonding types.
• The positive end (or pole) in a polar bond is represented
+ and the negative pole -.
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Drawing Lewis Structures
1.
2.
3.
4.
5.
6.
Follow Step by Step Method
Total all valence electrons. [Consider Charge]
1. Use Gr # on PT. ex Gr1=1v.e, Gr2=2ve etc
Write symbols for the atoms and guess skeleton structure
[ define a central atom ].
Place a pair of electrons in each bond.
Complete octets of surrounding atoms. [ H = 2 only ]
Place leftover electrons in pairs on the central atom.
If there are not enough electrons to give the central atom
an octet, look for multiple bonds by transferring
electrons until each atom has eight electrons around it.
Lewis Dot Diagrams for Individual Elements
Exceptions to the Octet Rule
•
•
•
•
Central Atoms Having Less than an Octet
Relatively rare.
Molecules with less than an octet are typical for
compounds of Groups 1A, 2A, and 3A.
Most typical example is BF3.
Formal charges indicate that the Lewis structure with an
incomplete octet is more important than the ones with
double bonds.
Exceptions to the Octet Rule
Central Atoms Having More than an Octet
• This is the largest class of exceptions.
• Atoms from the 3rd period onwards can accommodate
more than an octet.
• Beyond the third period, the d-orbitals are low enough in
energy to participate in bonding and accept the extra
electron density.
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Drawing Lewis Structures
Formal Charge
• Consider:
C N
• For C:
•
•
•
There are 4 valence electrons (from periodic table).
In the Lewis structure there are 2 nonbonding electrons and 3
from the triple bond. There are 5 electrons from the Lewis
structure.
Formal charge: 4 - 5 = -1.
Drawing Lewis Structures
Formal Charge
• Consider:
C N
• For N:
•
•
•
There are 5 valence electrons.
In the Lewis structure there are 2 nonbonding electrons and 3
from the triple bond. There are 5 electrons from the Lewis
structure.
Formal charge = 5 - 5 = 0.
• We write:
C N
Formal Charge facts to keep in mind:
Formal charges need to cancel out on a neutral
compound. Example SO3
Formal charges equal (when added) the total
charge of the compound. Example NO3-1
Molecular Shapes: VSEPR
• There are five fundamental geometries for molecular
shape:
Molecular Shapes – 3D Notations
VSEPR (Ballons)-Movie Clip
Figure 9.3
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Summary of VSEPR Molecular Shapes
e-pairs
Notation
Name of VSEPR shape Examples
2
AX2
Linear
HgCl2 , ZnI2 , CS2 , CO2
3
AX3
Trigonal planar
BF3 , GaI3
AX2E
Non-linear (Bent)
SO2 , SnCl2
AX4
Tetrahedral
CCl4 , CH4 , BF4-
AX3E
(Trigonal) Pyramidal
NH3 , OH3-
AX2E2
Non-Linear (Bent)
H2O , SeCl2
AX5
Trigonal bipyramidal
PCl5 , PF5
AX4E
Distorted tetrahedral
(see-sawed)
TeCl4 , SF4
AX3E2
T-Shaped
ClF3 , BrF3
AX2E3
Linear
I3- , ICl2-
AX6
Octahedral
SF6 , PF6-
AX5E
Square Pyramidal
IF5 , BrF5
AX4E2
Square Planar
ICl4- , BrF4-
4
5
6
Examples: VSEPR Molecular Shapes - I
# electron
pairs on
Central
Atom A
Notation
2
AX2
2 bp on A
AX3
3 bp on A
3
AX2E
2 bp and
1 lp on A
Example
Lewis
VSEPR & Name of Shape
Examples: VSEPR Molecular Shapes – I – F08
Examples: VSEPR Molecular Shapes - II
# electron
pairs on
Central
Atom A
Notation
AX4
4 bp on A
4
AX3E
3 bp and
1 lp on A
AX2E2
2 bp and
2 lp on A
Example
Lewis
VSEPR & Name of Shape
Examples: VSEPR Molecular Shapes – II – F08
Examples: VSEPR Molecular Shapes - III
# electron
pairs on
Central
Atom A
Notation
AX5
5 bp on A
AX4E
4 bp and 1
lp on A
5
AX3E2
3 bp and 2
lp on A
AX2E3
2 bp and 3
lp on A
Example
Lewis
VSEPR & Name of
Shape
Examples: VSEPR Molecular Shapes – III – F08
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Examples: VSEPR Molecular Shapes - IV
# electron
pairs on
Central
Atom A
Notation
AX6
6 bp on A
6
AX5E
5 bp and
1 lp on A
AX4E2
4 bp and
2 lp on A
Example
Lewis
VSEPR & Name of Shape
VSEPR Model
The Effect of Nonbonding Electrons
• By experiment, the H-X-H bond angle decreases on
moving from C to N to O:
H
H C H
H
109.5O
H N H
H
107O
O
H
H
104.5O
• Since electrons in a bond are attracted by two nuclei, they do
not repel as much as lone pairs.
• Therefore, the bond angle decreases as the number of lone pairs
increases
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VSEPR Model
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Figure 9.10: Shapes of Larger Molecules
• In acetic acid, CH3COOH, there are three central atoms.
Figure 8.10: Drawing Lewis Structures
Resonance Structures
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Figure 9.12
Figure 9.11: Molecular Shape and Molecular Polarity
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Figure 9.13: Molecular Shape and Molecular Polarity
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Covalent Bonding and Orbital Overlap
• Lewis structures and VSEPR do not explain why a bond
forms.
• How do we account for shape in terms of quantum
mechanics?
• What are the orbitals that are involved in bonding?
• We use Valence Bond Theory:
• Bonds form when orbitals on atoms overlap.
• There are two electrons of opposite spin in the orbital overlap.
Figure 9.14: Covalent Bonding and Orbital Overlap
VSEPR Model (Figure 9.6)
• To determine the electron pair geometry:
• draw the Lewis structure,
• count the total number of electron pairs around the central atom,
• arrange the electron pairs in one of the above geometries to
minimize e--e- repulsion, and count multiple bonds as one
bonding pair.
VSEPR
Model
Chemical Bonding
Types of Bonds
Ionic Bonding
Lewis Structures
Covalent Bonding
Resonance Structures
Octet Rule
Polar Molecules
Lewis
AXE notation
Molecular Geometries
VSEPR
Basic Shapes
3-D Notation
Hybridization (Lab)
VSEPR shapes
Polarity