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Heteroatomic Molecular Orbitals: Fill Mos in Order

This document discusses heteroatomic molecular orbitals using carbon monoxide and hydrogen fluoride as examples. It explains that heteroatomic molecular orbitals are formed by mixing atomic orbitals of similar energy and symmetry from each atom. The molecular orbital energies are estimated using diagrams and calculated using computer simulations. Configurations and terms are determined by filling the molecular orbitals in order of energy. Bond order is also discussed for hydrogen fluoride.

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281 views2 pages

Heteroatomic Molecular Orbitals: Fill Mos in Order

This document discusses heteroatomic molecular orbitals using carbon monoxide and hydrogen fluoride as examples. It explains that heteroatomic molecular orbitals are formed by mixing atomic orbitals of similar energy and symmetry from each atom. The molecular orbital energies are estimated using diagrams and calculated using computer simulations. Configurations and terms are determined by filling the molecular orbitals in order of energy. Bond order is also discussed for hydrogen fluoride.

Uploaded by

serna
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Heteroatomic molecular

orbitals
Heteroatomic molecular Carbon monoxide
orbitals
Physical Chemistry


Mix atomic orbitals
For discussion, treated
simplistically as one orbital
from each center
Lecture 25 Often close to correct
because a single orbital
Heteronuclear Diatomic Molecules predominates
Must mix orbitals of
Similar energy
Same symmetry
Molecular orbital energies
Rough estimation by
diagram
Calculated with computer
simulations

Example: carbon monoxide Example: carbon monoxide


Carbon monoxide
Atomic orbitals Hartree-Fock
2pC similar to 2pO calculations give 1 20.58 hartree
2sC similar to 2sO relative energies of
Allows an energy diagram
states 2 * 11.32 hartree
similar to homonuclear
diatomics Calculated with 3 1.55 hartree
Mixing occurs to create Gaussian
bonding and antibonding Not correct 4 * 0.79 hartree
states energies, but gives
Some mixing of 2s states
into the states from 2p
order of stability 1 0.64 hartree
Some mixing of 2p states Gives a filling order

into the states from 2s for producing 5 0.54 hartree
Produces a filling order for configurations
producing configurations

Determining configuration and


term of carbon monoxide Example 2: hydrogen fluoride
Fill MOs in order When atoms are of different energies, one must be
concerned with the relative energies and
Ground configuration symmetries of orbitals
(1)2(2*)2(3)2(4*)2(1)4(5)2 Orbitals of same symmetry and approximately similar
energy combine most effectively
Total angular momentum = 0 Can estimate approximate HF molecular orbitals
Total spin = 0 Energies calculated with Gaussian
Gives filling order of orbitals
Use term symbols as with 1 1sF 26.11 hartree
homonuclear diatomics 2 2sF


1.55 hartree
Note lack of indication of 1 3 C2 p0 F 1s H 0.71 hartree
inversion symmetry 1 2 p1F , 2 p1F 0.60 hartree
4 * D2 p0 F 1s H

1
Example 2: hydrogen fluoride Example 2: hydrogen fluoride
Finding ground configuration
Bond-order
10 electrons
Fill molecular orbitals in order 1 is a nonbonding orbital
2 is a nonbonding orbital
1 2 3 1
2 2 2 4

1 is a nonbonding orbital
Eigenvalues with respect to operations 3 is a bonding orbital
= 0 (all shells filled)

Consider only bonding and antibonding
S = 0 (all shells filled)
Even under reflection in vertical plane electrons
Term symbol 1
( 2 0) 1


BOHF
1 2

Example 3: hydrogen fluoride Example 4: Nitric oxide, NO


Excited configuration found by promoting a single
electron Fifteen (15) electrons
1 2 3 1 4
2 2 2 3 1 Use heteroatomic filling order
Eigenvalues of operators 1 2 2 2 3 2 1 4 4 2 (2 )3
Treat 3 electrons like 1 electron
The state of a hole is the state of an electron.
=1
Leads to term
S = 0, 1 (either paired or unpaired) S=
Terms that arise from this configuration Results ground-state term
1
3
2

Summary
Heteroatomic molecules are analyzed in a
manner similar to homoatomic molecules
Must know MOs
Must know filling order
MOs are more complex
Must involve atomic orbitals of similar energy and
symmetry
Energies calculated by computer
Hartree-Fock calculation relatively straightforward

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