localized electron model - mister chemistry
TRANSCRIPT
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Localized Electron Model
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Models for Chemical Bonding
Molecular orbital model
(Valence bond model)
Localized electron model
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Useful for explaining the structure of molecules especially nonmetals bonded to nonmetals
Localized Electron Model
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Electron pair can be shared when half-filled orbital of one atom overlaps with half-filled orbital of another.
δ Bond: orbitals overlap along the internuclear axis
Bond: side by side overlap of orbitals parallel to the internuclear axis
π
Localized electron model
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Distance of separation
0
Pote
ntia
l ene
rgy
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As the atoms approach each other, each electron is attracted by the nucleus of the other atom; at the same time, the electrons repel each other, as do the nuclei
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Bond in H2δ
δHH
H Hs s
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H2
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Bond in HFδ
1s 2p
F
H F
H
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F2
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Structure of Methane (CH4 )
structure of methane seems inconsistent with electron configuration of carbon
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carbon
2p
only two unpaired electrons
Carbon Should form δ −bonds with only two Hydrogen atoms ?2s
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Hybridization of AtomicOrbitals
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atomic orbitals obtained when two or nonequivalent orbitals of the same atom combine in preparation for covalent bond formation
Hybrid orbitals
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sp3 Hybridization
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Promote an electron from the 2s to the 2p orbital
2s
2p 2p
2s
sp3 Hybridization
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Mix together (hybridize) the 2s orbital and the three 2p orbitals
2 sp3
2p
2s
sp3 Hybridization
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2 sp3
Mix together (hybridize) the 2s orbital and the three 2p orbitals
sp3 Hybridization
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Shapes of orbitals
s p
sp3
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Bond in CH4δ
s sp3
CH
H CC Hδ
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The model is consistant with structure of methane
Allows for the formation of more bonds (4 rather than 2)
Bonds involving sp3 orbitals are stronger than s-s overlap or p-p overlap
Justification for OrbitalHybridization
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Four electron pairs
= tetrahedral arangement of those electron pairs
Remember
= sp3 hybridization
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tetrahedral arrangement of electron pairs Four electron pairs
C
N
:S:
:
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N
:2 sp3
NH3
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sp Hybridization
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Promote an electron from the 2s to the 2p orbital
2s
2p 2p
2s
Beryllium chloride ( BeCl2 )
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2p
2s
Beryllium chloride ( BeCl2 )
Mix together (hybridize) the 2s orbital and one 2p orbitals
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2p
2sp
Beryllium chloride ( BeCl2 )
Mix together (hybridize) the 2s orbital and one 2p orbitals
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The Be Cl δ Bond in BeCl
p spCl Be
Cl Be
Be Cl
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Cl Be
The Be Cl δ Bond in BeCl
p spCl Be
Cl
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sp2 Hybridization
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Boron trifloride
Promote an electron from the 2s to the 2p orbital
2p
2s2s
2p
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Boron trifloride Mix together (hybridize) the 2s orbital and two 2p orbitals
2p
2s
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Boron trifloride
2 sp2
2p
Mix together (hybridize) the 2s orbital and two 2p orbitals
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B
F
Boron trifloride
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B
F
F
F
Boron trifloride
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hybrid orbitals are used only for atoms in a molecule,
Hybridizing Atomic Orbitals
hybrid orbitals are different in shape from the atomic orbitals from which we derive themnumber of hybrid orbitals equals number of atomic orbitals from which they were generated
hybridization permits more bonds and stronger bondscovalent bond results from overlap of half-filled orbitals
not for isolated atoms
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draw the Lewis structure of the molecule
Procedure For Hybridizing Atomic Orbitals
predict the overall arrangement of the electron pairs using the VSEPR model
deduce the hybridization of the central atom
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PF5SF6
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Hybridization of s, p, and d Orbitals
Beginning with the third period of the periodic table 1 3s orbital + 3 3p orbital + 1 3d orbital
gives sp3dPermits five electron pairs ( trigonal bipyramidal )
1 3s orbital + 3 3p orbital + 2 3d orbital
Permits six electron pairs ( octahedral )
gives sp3d2
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π -Bonds
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Review :Valence bond model
Electron pair can be shared when the half-filled orbital of one atom overlaps with half-filled orbital of another.
δ Bond: orbitals overlap along the internuclear axis
Bond: side by side overlap of orbitalsπ
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Structure of EthyleneC2H4
CH2 CH2
planar
Bond angle 120 °
Requires hybridization different from sp3
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Promote an electron from the 2s to the 2p orbital
2s
2p 2p
2s
Orbital Hybridization
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Orbital Hybridization
2p
2s
Mix together (hybridize) the 2s orbital and the two 2p orbitals
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2 sp2
2p
Orbital HybridizationMix together (hybridize) the 2s orbital and the two 2p orbitals
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Lewis model : Ethylene
HC
H
H
HC
The carbon-carbon double bond of ethylene is a combination of an
δ Bond
δ Bond
Bondπ
Bondπ and
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−Bonding in Ethyleneπ
2 sp2
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sp2
−Bonding in Ethyleneπ
2p
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−Bonding in Ethyleneπ
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−Bonding in Ethyleneπ
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