Chapter 1: Structure and Bonding

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Chapter 1 Structure and Bonding
Coverage 1. Electron Configurations and
review 2. Lewis Structures 2. Covalent and Ionic
bonds 3. Atomic and Molecular Orbitals 4.
Hybridization

• Goals
• Be able to write the electron configuration for
  C, N, O, S, and P.
• Be able to write Lewis line bond structures for
  simple organic molecules.
• Know the definitions of a sigma and pi bonds.
• Be able to predict the number of sigma and pi
  bonds in a molecule.
• Be able to predict the hybridization of an atom
  in a molecule.
• Be able to predict the approximate bond angles in
  a molecule.

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Linus Pauling 1901-1994 Nobel Prize Chemistry
1954 Nobel Prize Peace 1963 Chemical bonding,
medicine, biology
Both independently recognized that carbon atoms
link together to form carbon chains. Kekule
proposes that carbon is tetravalent
For more see http//www.chemheritage.org/Educatio
nalServices/chemach/home.html
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Orbitals and Wave Functions

• Bohr and Quantum Mechanical Method
• de Broglie electrons have wave properties
• Y Wave Function that describes orbital
• Y2 Electron Density around Nucleus

2s
2p
1s
Analogy Guituar String
and indicate mathematical sign of wave, not
charges!
1s orbital
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See HyperChem 3-D Model
2p orbital
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Atomic and Molecular Orbitals

• Guidelines for Combining Atomic Orbitals
• 1. Atomic Orbitals (AOs) on different atoms
  combine to produce Molecular Orbitals (Mos) that
  are bonding or antibonding.
• This is referred to as a Linear Combination of
  Atomic Orbitals (LCAO).
• MO1 aAO1 bAO2 c AO3 where a,b,c are
  coefficients.
• Each AO results in an MO. For example, if three
  AOs are used to construct the MOs, then three MOs
  must result.
• 3. When AOs on the same atom combine they
  produce hybrid AOs.

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H2 Molecule
s
In the Ground State, the Antibonding MO is empty.
Antibonding MO
.
1s AO
1s AO

• s

In the Ground State, the Bonding MO has two
electrons
Bonding MO
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Sigma Bond (s) covalent bond that is symmetric
about the bond axis.
s orbitals of H interacting to form sigma bond.
p orbital interacting end-on-end to form sigma
bond
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Pi (p) Bond
p
In the Ground State, the Antibonding MO is empty.
Antibonding MO
.
.
2p AO
2p AO

• p

In the Ground State, the Bonding MO has two
electrons
Bonding MO
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Two atomic p orbitals
Pi (p) Bond
3D view of Pi (p) Bond

• (pi) Bond overlap of two p orbitals oriented
  perpendicular
• to the line connecting the
  nuclei.

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Hybridization of Atomic Orbitals

• AOs on a single atom mix to form new, hybrid
  orbitals. These hybrid orbitals
• have characteristics of both s and p orbitals.
• Provides a means of explaining observed bond
  angles in organic molecules.
• Acetylene

sp
sp
180o
__ __ __ p
E
__ __ __
__ __ p __ __ sp hydrid
promote e-
Mix orbitals
__ s
__
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s p
sp
sp
z
Remember, there are two p orbitals leftover and
these would be located on the y and z axes.
y
Each sp orbital possesses 50 s character and 50
p character.
x
Two sp orbitals
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Orbital Picture of Acetylene
?
?
C C
?
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sp2 sp2
Ethylene
The carbon atom is sp2 hybridized to obtain
trigonal planar geometry
__ __ __ p
E
__ __ __
__ p __ __ __ sp2 hydrid
Promote e-
Mix orbitals
__ s
__
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sp2 Hybridization

s 2 p
There is one p orbital left over, and it would be
along the z axis.
3 sp2 orbitals
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Orbital Picture of Ethylene
px
px
?
sp2
sp2
?
?
C C
?
sp2
sp2
sp2
sp2
?
?
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Methane
sp3
The carbon atom is sp3 hybridized to obtain
tetrahedral geometry. All bond angles are equal
at 109.50.
__ __ __ p
E
__ __ __
__ __ __ __sp3
Promote e-
Mix orbitals
__ s
__
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s 3 p
4 sp3 orbitals
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Orbital Picture of Methane
?
sp3
?
sp3
?
sp3
sp3
?