Valence Bond Theory - ic.arc.losrios.edu
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Bonds between atoms occur when the orbitals on those atoms interacted to make a bond A covalent bond forms when the orbitals of two atoms overlap and a pair of electrons occupy the overlap region. The space formed by the overlapping orbitals can accommodate a maximum of two electrons and these electrons must have opposite (paired) spins. The greater the orbital overlap, the stronger the bond. The extent of orbital overlap depends on: orbital shape and direction whether the orbitals align along the axis between the nuclei, or outside the axis Valence Bond Theory As two atoms approached, the half-filled valence atomic orbitals on each atom would interact to form molecular orbitals regions of high probability of finding the shared electrons in the molecule more stable than the separate atomic orbitals because they would contain paired electrons shared by both atoms Valence Bond Theory 1 2
Transcript of Valence Bond Theory - ic.arc.losrios.edu
Bonds between atoms occur when the orbitals on those atoms interacted to make a bond
A covalent bond forms when the orbitals of two atoms overlap and a pair of electrons occupy the overlap region.
The space formed by the overlapping orbitals can accommodate a maximum of two electrons and these electrons must have opposite (paired) spins.
The greater the orbital overlap, the stronger the bond.
The extent of orbital overlap depends on: orbital shape and direction
whether the orbitals align along the axis between the nuclei, or outside the axis
Valence Bond Theory
As two atoms approached, the half-filled valence atomic orbitals on each atom would interact to form molecular orbitals
regions of high probability of finding the shared electrons in the molecule
more stable than the separate atomic orbitals because they would contain paired electrons shared by both atoms
Valence Bond Theory
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Valence Bond Theory
H2S
Valence Bond Theory
CH4
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Some atoms hybridize their orbitals to maximize bonding
more bonds = more full orbitals = more stability
Same type of atom can have different types of hybridization
C = sp, sp2, sp3
Hybridizing is mixing different types of atomic orbitals in the valence
shell to make a new set of degenerate hybrid orbitals
sp, sp2, sp3, sp3d, sp3d2
Valence Bond Theory
Valence Bond Theory
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The number of atomic orbitals combined = the number of hybrid orbitals formed combining one s orbital with three p orbital gives
H cannot hybridize!! its valence shell only has one orbital
The number and type of atomic orbitals combined determines the shape of the hybrid orbitals
Valence Bond Theory
Valence Bond Theory
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Unhybridized
2s2p
Valence Bond Theory# of orbitals
sp3 hybridized C
HH H
H
sp2 hybridized2p
sp2
C
O
H H
sp2sp2
2p 2p
sp hybridized
sp2p
N C H
sp2p
sp3sp3 sp3 sp3
Place electrons into hybridized and unhybridized valence orbitals as if all the orbitals have equal energy
Valence Bond Theory
unhybridized C atom
2s2p2p 2p
sp3 hybridized C atom
sp3 sp3 sp3sp3
sp2 hybridized C atom
sp2 sp2
2p
sp2
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Valence Bond Theory
unhybridized N atom
2s2p 2p2p
sp3 hybridized N atom
sp3 sp3 sp3sp3
Place electrons into hybridized and unhybridized valence orbitals as if all the orbitals have equal energy
Lone pairs generally occupy hybrid orbitals
sp hybridized P atom
sp
3p 3p
sp
Bonding takes place between atoms when their atomic or hybrid orbitals interact (“overlap”)
Valence Bond Theory
To interact, the orbitals must either be aligned along the axis between the atoms, or
The orbitals must be parallel to each other and perpendicular to the interatomic axis
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A sigma () bond results when the interacting atomic orbitals point along the axis connecting the two bonding nuclei
A pi () bond results when the bonding atomic orbitals are parallel to each other and perpendicular to the axis connecting the two bonding nuclei
The interaction between parallel orbitals is not as strong as between orbitals that point at each other; therefore bonds are stronger than bonds
Valence Bond Theory
“Overlap” between a hybrid orbital on one atom with a hybrid or unhybridizedorbital on another atom results in a bond
“Overlap” between unhybridized p orbitals on bonded atoms results in a bond
Valence Bond Theory
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Valence Bond Theory
H C N
H
H
H
H
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Valence Bond Theory
C
O
H H
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The number of atomic orbitals combined = the number of hybrid orbitals formed combining one s orbital with two p orbital gives
In this case,
H cannot hybridize!! its valence shell only has one orbital
The number and type of atomic orbitals combined determines the shape of the hybrid orbitals
Valence Bond Theory
Valence Bond Theory
Hybrid orbitals overlap to form a bond.
Unhybridized p orbitals overlap to form a bond.
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Because the orbitals that form the bond point along the internuclear axis, rotation around that bond does not require breaking the interaction between the orbitals
Valence Bond TheoryThe orbitals that form the bondinteract above and below the internuclear axis, so rotation around the axis requires the breaking of the interaction between the orbitals
Valence Bond Theory
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The number of atomic orbitals combined = the number of hybrid orbitals formed combining one s orbital with one p orbital gives
In this case, there must be
H cannot hybridize!! its valence shell only has one orbital
The number and type of atomic orbitals combined determines the shape of the hybrid orbitals
Valence Bond Theory
Valence Bond Theory
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Valence Bond Theory
C NH
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The number of atomic orbitals combined = the number of hybrid orbitals formed combining one s orbital with three p orbitals and one d orbital gives
In this case, there must be
H cannot hybridize!! its valence shell only has one orbital
The number and type of atomic orbitals combined determines the shape of the hybrid orbitals
Valence Bond Theory
Valence Bond Theory
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Valence Bond Theory
S
O
FF
F F
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The number of atomic orbitals combined = the number of hybrid orbitals formed combining one s orbital with three p orbitals and one d orbital gives
In this case, there must be
H cannot hybridize!! its valence shell only has one orbital
The number and type of atomic orbitals combined determines the shape of the hybrid orbitals
Valence Bond Theory
Valence Bond Theory
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Valence Bond Theory
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“The Dreaded Turtle”
C C
H
H Cl
H
OS
O
OSO3
2–
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