This ppt describe you Molecular orbital energy level diagram, bond order, stabilization energy and magnetic properties of C2, Be2, N2, O2, and F2 molecules

1. Series of lecture on
Bonding in Molecules
Lecture-7
Molecular Orbital
Theory: Part- III
MO energy level diagram, Bond Order,
Stabilization energy, magnetism,
of B2, C2, N2 O2 and F2 molecules
D. R. Shinde
Associate Professor in
ChemistryDepartment of Chemistry
P.D.E.A’s.
Prof. Ramkrishna More
Arts, Commerce and Science College
Akurdi, Pune-411044
1

2. i. Formation of B2, C2, N2, O2 and F2 molecules
ii. MO energy level diagram
iii. Bond Order, Stabilization energy and magnetism
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
2

3. Formation of B2, C2 , N2, O2, F2, Ne2
Molecules
Electronic configuration of elements
B (At. No.-5) is – 1s2, 2s2, 2p1
C (At. No.-6) is – 1s2, 2s2, 2p2
N (At. No.-7) is – 1s2, 2s2, 2p3
O (At. No.-8) is – 1s2, 2s2, 2p4
F (At. No.-9) is – 1s2, 2s2, 2p5
Ne (At. No.-10) is – 1s2, 2s2, 2p6
All these elements consists of full
filled 1s orbital in inner shell.
Hence it cannot take part in
bonding in the molecules.
Valence shell 2s and 2p orbital of
these elements are suitable in
energy and size hence they will
take part in bonding i.e. can
combine to form MO’s.
All these elements can form diatomic
molecules. For all these elements
common thing is that AO that can
take part in bonding are same.05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
3

4. How 2s and 2p orbitals of on atom can interact with other atom?
Depending on symmetry properties and energies the possible interactions between
AO are -
 2s – 2s
 2pz – 2pz
 2py-2py
 2px-2px
 2s – 2s and 2pz – 2pz: These two interactions take
place long inter nuclear axis hence these two
interactions results into formation sigma MO’s.
 2py-2py and 2px-2px: These two interactions take
place perpendicular to inter nuclear axis hence
these two interactions results into formation pi
MO’s.05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
4

5. ++ + or -
2s-2s interaction Bonding MO σ2s
+
Anti-Bonding MO σ*2s
++ - -
+
pz -pz intraction
+
-
+
-
Bonding MO σ2pz
+
- -
Anti-Bonding MO σ*2s
+- -+
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
5

6. +
+
+
-
px –px or py-py
Interaction
+
-
Bonding MO π2px
Anti-Bonding MO π*2px
+ -
-
If you calculated, in the formation of diatomic
molecule, 4 orbitals from each atom will take part in
bonding. Thus, from two atoms 8 AO will form 8 MO
in molecule. Hence, now one can construct MO
energy level diagram for the molecule.
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
6

7. General MO Energy Level Diagram and Labeling of MO
σ*2s
σ2s
2p 2p
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s 2s
Energy
AO of atom-1 AO of atom-2
MO’s
MO energy level diagram
+
++ - -
+
- -
+
-
+
-
+- -+
+ -
-
+ -
-
σ2s
σ*2s
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz Energies of AO’s: 2s < 2p
Energies of MO’s
σ2s < σ*2s, < σ2pz< π2px= π2py
< π*2py = π*2px < σ*2pz
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
7

8. On the basis of this MO energy level diagram we can explain formation of N2, O2,
F2 molecules, while small modification is required in MO energy level diagram for
the explanation of B2 and C2 Molecules.
Very first criterion is to explain magnetic properties of molecules on the basis of
electronic configuration of molecule.
Molecule may be diamagnetic or paramagnetic.
Diamagnetic – all electrons in MO are in paired state
Paramagnetic – One or more electrons in MO are in unpaired state.
Magnetic properties of molecule are obtained practically.
Thus, the practically, B2, O2 molecules are found to be paramagnetic while
molecules C2, N2 and F2 were found diamagnetic.
Thus, keeping magnetic properties in mind we have to construct MO energy level
diagram for these five molecules.
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
8

9. The Case of B2 molecules
↑↓ ↑↓
σ*2s
σ2s
↑↑↑ ↑↑↑
2p1 2p1
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of B AO of B
MO’s of B2
MO energy level diagram for B2 molecule
 Electronic configuration of B (At. No.-5) is – 1s2, 2s2, 2p1
 Electronic configuration of B2 molecule: [kk]
(σ2s)2, (σ*2s)2, σ2pz
2
 B2 molecule is paramagnetic, and it has two unpaired
electrons
 According to this MO energy level diagram B2
molecule is diamagnetic.
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
9

10. The Case of B2 molecules
↑↓ ↑↓
σ*2s
σ2s
↑ ↑
2p1 2p1
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of B AO of B
MO’s of B2
MO energy level diagram for B2 molecule
 Thus, some modification is required in this MO energy
level diagram.
 To have two unpaired electrons σ2pz MO must have
higher energy than π-2(px, py) MO’s. Then two unpaired
electrons will be there in π-2(px, py) orbitals.
 Now electronic configuration of B2 molecule: [kk]
(σ2s)2, (σ*2s)2, (π2px)1, (π2py)1. This is correct order
of MO’s since it explain the paramagnetism of B2
molecule.
σ2pz
π2(px, py)
Stabilization Energy
= (4 × – Δ) – (2 × +Δ)
= – 2Δ
Bond Order = = 1
4 - 2
2
 B2 molecule may be formed but will be very less stable as there is only pi bond.05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
10

11. ↑↓ ↑↓
σ*2s
σ2s
↑ ↑
2p2 2p2
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of C AO of C
MO’s of C2
MO energy level diagram for C2 molecule
σ2pz
π2(px, py)
↑ ↑
The Case of C2 molecules
 The MO energy level diagram of C2 is similar to
boron.
 Thus, electronic configuration of C2 molecule:
[kk] (σ2s)2, (σ*2s)2, (π2px)2, (π2py)2. This is
correct order of MO’s since it explain the
diamagnetism of C2 molecule.
 Electronic configuration of C (At. No.-6) is – 1s2, 2s2, 2p2
 C2 molecule is diamagnetic i.e. all electrons are paired.
Stabilization Energy
= (6 × – Δ) – (2 × +Δ)
= – 4Δ
Bond Order = = 2
6 - 2
2
σ2pz Orbital is higher in energy than π2pxand π2py.
 C2 molecule, bond order=2,
but have pi bonds only, Thus
it may be formed but will be
very less stable.
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
11

12. ↑↓ ↑↓
σ*2s
σ2s
MO energy level diagram for N2 Molecule:
 Electronic configuration of N (At. No.-7) is – 1s2, 2s2, 2p3
 The filled 1s orbital of two N atom cannot take part in
bonding as it is inner shell orbital.
 Valence shell 2s and 2p orbital of two N atom can combine
to form MO’s.
 The eight MO formed in N2 molecule are - σ2s, σ*2s,
π2px, π2py, σ2pz, π*2py, π*2px, σ*2pz.
 Electronic configuration of N2 molecule – 10 electrons
are to filled in MO’s: [kk], (σ2s)2, (σ*2s)2, (π2px)2,
(π2py)2
, σ2pz
2.
↑↑↑ ↑↑↑
2p3 2p3
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of N AO of N
MO’s of N2
MO energy level diagram for N2 molecule
 N2 molecule, bond order=3, It is highly stable.
 It is diamagnetic in nature as all electrons are
in paired state.
Bond Order = = 3
8 - 2
2
Stabilization Energy
= (8 × – Δ) – (2 × +Δ)
= – 6Δ
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
12

13. ↑↓ ↑↓
σ*2s
σ2s
↑↓↑↑ ↑↑↑ ↓
2p4 2p4
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of O AO of O
MO’s of O2
MO energy level diagram for O2 molecule
MO energy level diagram for O2 Molecule:
 Electronic configuration of O (At. No.-8) is – 1s2, 2s2, 2p4
 The filled 1s orbital of two O atom cannot take part in
bonding as it is inner shell orbital.
 Valence shell 2s and 2p orbital of two O atom can combine
to form MO’s.
 The eight MO formed in O2 molecule are - σ2s, σ*2s,
σ2pz, π2px, π2py, π*2py, π*2px. σ*2pz.
 Electronic configuration of O2 molecule: 12 electrons are
to filled in MO’s[kk], (σ2s)2, (σ*2s)2, σ2pz
2
, (π2px)2,
(π2py)2 (π*2px)1, (π*2py)1
 O2 molecule, bond order=2, It is highly stable.
 In consists of 2 electrons in unpaired state.
Therefore, it is paramagnetic in nature
Bond Order = = 2
8 - 4
2
Stabilization Energy
= (8 × – Δ) – (4 × +Δ)
= – 4Δ
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
13

14. ↑↓ ↑↓
σ*2s
σ2s
↑↓↑↑ ↑↑↓↑↓
2p4 2p5
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of O AO of O- ion
 O2 molecule can form O2
- (oxygen superoxide)
ion by gain of one electron.
 It is paramagnetic in nature as it consists of one
unpaired electron.
Thus Bond Order = = 1.5
8 - 5
2
MO’s of O2
-
MO energy level diagram for O2
- molecule
05/08/2020 D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
14

15. ↑↓ ↑↓
σ*2s
σ2s
↑↓↑↑ ↑↑↑ ↓
2p4 2p4
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of O AO of O
 O2 molecule can form O2
2- (superoxide ion)
ion. It is formed by gain of two electron by O2.
 It is diamagnetic in nature as it consists of all
electrons in paired state.
Thus Bond Order = = 1.0
8 - 6
2
MO’s of O2
2-
MO energy level diagram for O2
2- molecule
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
15

16. MO energy level diagram for F2 Molecule:
 Electronic configuration of F (At. No.-9) is – 1s2, 2s2, 2p5
 The filled 1s orbital of two F atom cannot take part in
bonding as it is inner shell orbital.
 Valence shell 2s and 2p orbital of two F atom can combine
to form MO’s.
 The eight MO formed in F2 molecule are - σ2s, σ*2s,
σ2pz, π2px, π2py, π*2py, π*2px. σ*2pz,
 Electronic configuration of F2 molecule: 14 electrons are
to filled in MO’s. [kk], (σ2s)2, (σ*2s)2, σ2pz
2
, (π2px)2,
(π2py)2 (π*2px)2, (π*2py)2
 F2 molecule, bond order=1, It is highly stable.
 In consists of all electrons in paired state.
Therefore, it is diamagnetic in nature.
Bond Order = = 1
8 - 6
2
Stabilization Energy
= (8 × – Δ) – (6 × +Δ)
= – 2Δ
↑↓ ↑↓
σ*2s
σ2s
↑↓↑↓↑ ↑↑↓↑↓
2p5 2p5
σ2pz
π2(px, py)
Π*2(px, py)
σ*2pz
2s2 2s2
Energy
AO of F AO of F
MO’s of F2
MO energy level diagram for F2 molecule
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
16

17. In Summary
1. We have seen formation of B2, C2, N2 O2 and F2 molecules on the basis of MOT
2. MO energy level diagram and electronic configuration of these molecules.
3. We have predicted bond order and magnetic properties of these molecules.
05/08/2020
D. R. Shinde, Asociate Prof., P.D.E.A's. Prof Ramkrishna More
College, Akurdi, Pune
17