1 molecular orbitals in chemical bonding. 2 molecular orbital theory ztypes of molecular orbitals...
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1
Molecular Orbitals in Chemical Bonding
2
Molecular Orbital Theory
Types of molecular orbitals that can be produced by the overlap of atomic orbitals.Head-on overlap of atomic orbitals produces
(sigma) orbitals.Side-on overlap of atomic orbitals produces
(pi) orbitals.Two s atomic orbitals can overlap and
produce two molecular orbitals designated as a s and a s
* molecular orbital.
3
Molecular Orbital Theory
Graphically we can represent this as
4
Molecular Orbital Theory
5
Molecular Orbital Theory
6
Molecular Orbital Theory
The head-on overlap of two corresponding p atomic orbitals on different atoms, say px with px produces p and p
* molecular orbitals.
7
Molecular Orbital Theory
8
Molecular Orbital Theory
Side-on overlap of two corresponding p atomic orbitals on different atoms (say py with py or pz with pz) produces and (pi) molecular orbitals.
9
Molecular Orbital Theory
10
Molecular Orbital Energy-Level Diagram
Order of filling of MO’s obeys same rules as for atomic orbitals.
Including Aufbau principle Hund’s Rule
11
Molecular Orbital Energy-Level Diagram
12
Bond Order and Bond Stability
Bond order (bo) of a molecule is defined as half the number of electrons in bonding orbitals minus half the number of electrons in antibonding orbitals
bo =
# e in bonding orbitals # e in antibonding orbitals
2
- -
13
Homonuclear Diatomic Molecules
Consider the overlap of the atomic orbitals of two nitrogen atoms to form an N2 molecule.
Each N atom has 7 electrons thus the N2 molecule has 14 electrons.
14
Homonuclear Diatomic Molecules
15
Homonuclear Diatomic Molecules
In shorthand notation we represent this configuration as
N 2 1s2
1s*2
2s2
2s*2 2
22 2
2p p py y
*2
16
Homonuclear Diatomic Molecules
The greater the bond order of a bond the more stable we predict it to be.
For N2 the bond order is
theory VB in bond
a triple toingcorrespond 32
62
4-10bo
17
Homonuclear Diatomic Molecules
MO treatment can also be applied to ions. Ions are charged and that charge affects the stability as well as the
bond order. Write out the electron configuration of the N2
+ ion in abbreviated notation (s
2 s*2……). What is the bond order?
18
Homonuclear Diatomic Molecules
Write out the electron configuration of the N2
+ ion in abbreviated notation (s2
s*2……). What is the bond order?
21
-
12
2*2
22
*22s
22s
*21s
21s
+2
22
4-9=bo
e 13 of total
N
xzy ppp
19
Homonuclear Diatomic Molecules
Write out the electron configuration of the O2 molecule in abbreviated notation. What is the bond order? Is the molecule paramagnetic or diamagnetic?
20
Homonuclear Diatomic Molecules
Write out the electron configuration of the O2 molecule in abbreviated notation.
What is the bond order? Is the molecule paramagnetic or diamagnetic?
icparamagnet is O -ally experiment
cdiamagneti is O that predicts theory BondValence
icparamagnete unpaired 2
22
6-10=bo
O
2
2
-
1*2
1*2
22
22
22
*22s
22s
*21s
21s2
zyzyx ppppp
21
Homonuclear Diatomic Molecules
Write out the electron configuration of the Be2 molecule in abbreviated notation. What is the bond order? Would you predict that the molecule exists?
You do it!
22
Homonuclear Diatomic Molecules
Write out the electron configuration of the Be2 molecule in abbreviated notation.
What is the bond order? Would you predict that the molecule exists?
exist. toexpectednot is Be
0, oforder bond a hasit Since
02
4-4=bo
Be
2
*22s
22s
*21s
21s2
23
Homonuclear Diatomic Molecules
Write out the electron configuration for F2.
In this molecule the p molecular orbital is lower than the p molecular orbitals. What is the bond order? Is F2 paramagnetic?
24
Homonuclear Diatomic Molecules
Write out the electron configuration for F2.
In this molecule the p molecular orbital is lower than the p molecular orbitals. What is the bond order? Is F2 paramagnetic?
cdiamagnetie unpaired No
12
8-10=bo
F
-
2*2
2*2
22
22
22
*22s
22s
*21s
21s2
zyzyx ppppp
25
Delocalization and Shapes of Molecular Orbitals
Valence bond theory discusses resonance formulas. Carbonate ion (CO3
2-) is an example.
OC
O
O
2-
OC
O
O
2-
OC
O
O
2-
26
Delocalization and Shapes of Molecular Orbitals
Molecular orbital theory describes shapes in terms of delocalization of electrons. Again carbonate ion (CO3
2-) is a good example.
O
C OO
O
C OO
O
C OO
27
Delocalization and Shapes of Molecular Orbitals
The structure of benzene is described well by molecular orbital theory.
28
Delocalization and Shapes of Molecular Orbitals
Resonance structure - VB theory.
29
Delocalization and Shapes of Molecular OrbitalsMolecular orbital theory
30
Delocalization and Shapes of Molecular OrbitalsMolecular orbital theory
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