Transcript hybrid - River Dell Regional School District

Molecular Geometry and
Polarity
Part I: Molecular Geometry –
Valence Bond Theory (B)
Dr. Chin Chu
River Dell Regional High School
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Valence Bond Theory
Combines bonding with geometry.
Addresses the equality of bonds in a
molecule as far as length and energy
are concerned.
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Valence Bond Theory
• Explains the structures of covalently bonded
molecules
– ‘how’ bonding occurs
Principles of VB Theory:
Bonds form from overlapping atomic orbitals
and electron pairs are shared between two
atoms
A new set of hybridized orbitals may form
out of necessity.
Lone pairs of electrons are localized on one
atom
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4
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Hybridization
• When atomic orbitals on the central atom do not
provide sufficient number of orbitals with single
electron for proper bonding with surrounding
atoms, mixing of atomic orbitals to produce
hybrid orbitals with proper orientation in 3D
space provides a viable solution.
• The mixing of several atomic orbitals to form the
same number of hybrid orbitals.
• All the hybrid orbitals that form are the same in
shape and energy but differing in orientation in 3D
space.
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sp3 hybridization
One -s orbitals and 3 – p orbitals
blended to give four identical
hybrid sp3 orbitals
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sp3 hybridization
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sp3 hybridization
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Geometry?
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Hybridization
• We blend the s and p orbitals of the
valence electrons and end up with the
tetrahedral geometry.
• We combine one s orbital and 3 p orbitals.
• sp3 hybridization has tetrahedral
geometry.
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3
sp geometry
• This leads to
tetrahedral shape.
• Every molecule with a
total of 4 atoms and
109.5º
lone pair is sp3
hybridized.
• Gives us trigonal
pyramidal and bent
shapes.
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sp2 Hybridization
We mix 1 – s orbital with 2- p
orbitals to produce three identical
hybrid sp2 orbitals
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Examples? BF3, C2H4, AlCl3
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Where is the P orbital?
• Perpendicular
• The overlap of
orbitals makes
a sigma bond
(s bond)
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sigma bonds in ethene
H
H
C
H
pi bonds in ethene
C
H
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Ethene, sp2 hybridization
Geometry?
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sp2 hybridization in C2H4
•
•
•
•
trigonal planar
120º angle
one p bond
One sigma and one pi bond between the
C-C atoms
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sp Hybridization
We combine an s – orbital with a –
p orbital to form two identical
hybrid sp orbitals
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Bonding in BeCl2: sp Orbital overlap
Lone pairs of Cl stay in the p- atomic orbitals
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What about sp
• one s and one p hybridize
• Linear
• C 2H 2
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sp hybridization
• end up with two lobes 180º
apart.
• p orbitals are at right angles
• makes room for two p bonds
and two sigma bonds.
• a triple bond or two double
bonds possible
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Ethyne
sp hybridization + pi bonds
sp3d Hybridization
Geometry?
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sp3d2 Hybridization
Geometry?
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To predict the hybridization of the central atom:
Count the number of lone pairs AND the number
of atoms bonded to the central atom. What is the
GEOMETRY of electron pairs?
# of Lone Pairs
+
# of Bonded Atoms
Hybridization
Examples
2
sp
BeCl2
3
sp2
BF3
4
sp3
CH4, NH3, H2O
5
sp3d
PCl5
6
sp3d2
SF6
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Hybridization and Geometry of
Electrons
•
•
•
•
•
•
sp3: tetrahedral
sp2: trigonal planar
sp: linear
sp3d: trigonal bipyramid
sp3d2: octahedral
Geometry of molecule determined
by number of shared and unshared
electrons.
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Types of Hybrid Orbitals: Summary
• sp3 : 1 s and 3 p orbitals mix to form 4 sp3
orbitals.
• sp2 :1 s and 2 p orbitals mix to form 3 sp2
orbitals leaving 1 p orbital intact.
• sp : s and 1 p orbitals mix to form 4 sp
orbitals leaving 2 p orbitals intact.
• sp3d: five orbitals
• sp3d2 : six orbitals
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