+ wave mechanics and covalent bond formation ch 9
TRANSCRIPT
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Wave Mechanics and Covalent Bond Formation
Ch 9
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+2 successful theories approach the formation of a covalent bond Valence Bond Theory
Covalent bond is the overlapping of 2 atomic orbitals when electron spins are paired
AP exam tends to focus on the VB approach
Molecular Orbital Theory Considers that a molecule
is similar to an atom in that both have distinct energy levels that can be populated with electrons
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+Valence Bond Theory
2 H atoms approach & interact w/ an overlap of their atomic orbitals with e- that have opposing spins
When the bond forms, the paired e- spread out over the molecule to form the final e- cloud over the nuclei.
Overlap of 2 “s” orbitals – called a SIGMA (σ)BOND
- Every covalent bond has 1 & only 1 σ bond!
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Overlap of an “s” & a “p” orbital
Overlap of 2 “p” orbitals
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Pi (π) bonds Occur if there are double or triple bonds in the molecule Formed by the sideways overlap of 2 “p” orbitals e- density is arranged in the 2 e- clouds, one above and one
below the internuclear axis, so the e- in the π bond do NOT interfere with the σbond
Single bond – 1 σbond
Double bond – 1σbond & 1 π bond
Triple bond - 1σbond & 2 π bonds
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Which represents a double bond and which represents a triple bond?
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+Hybrid Orbital Model
VSEPR theory explains why certain molecules have the geometric shapes that are measureable in the lab.
Hybrid orbitals describe how the e- might rearrange in a molecule to explain the experimental data on bond angles. Hybrid orbital – a set of orbitals with identical
properties formed from the combination of 2 or more different orbitals with different energies
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+sp3 hybrid orbitalsEx. CH4
Structure is tetrahedral, the C has 4 σbonds
e- configuration
1s22s22p2
sp3 hybrid orbital
The “s” and 3 “p” orbitals in C reorganize into 4 sp3 hybrid orbitals. Notice that an sp3 orbital has energy somewhere between the 2s and the 2p
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+sp2 hybrid orbitals Ex. CH2O
sp2 hybrid orbitals The C has 3σbond & 1π bond
Structure is trigonal planar.
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+sp hybrid orbitals
The C has 2σbonds & 2 π bonds It’s linear
sp hybrid orbital
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+Correspondence between hybridization and structure
Structure Hybrid # bonding pairs
# lone pairs
Linear sp 2 0
Trigonal planar sp2 3 0
Bent sp2 2 1
Tetrahedral sp3 4 3
Trigonal pyramidal
sp3 3 1
Bent sp3 2 2
Scientists have NOT been able to demonstrate the existence ofand importance of sp3d and sp3d2 hybrid orbitals and are omitted from the AP Test. Therefore, all other structures will not be shown with their hybridization.