CONTENTS  INTRODUCTION  CONCEPTS OF WALSH DIAGRAM  APPLICATION IN TRIATOMIC MOLECULES [IN AH₂ TYPE OF MOLECULES(BeH₂,BH₂,H₂O)] INTRODUCTION Arthur Donald Walsh FRS The introducer of walsh diagram (8 August 1916-23 April 1977) was a British chemist, professor of chemistry at the University of Dundee . He was elected FRS in 1964. He was educated at Loughborough Grammar School. Walsh diagrams were first introduced in a series of ten papers in one issue of the Journal of the Chemical Society . Here, he aimed to rationalize the shapes adopted by polyatomic molecules in the ground state as well as in excited states, by applying theoretical contributions made by Mulliken .

1. WALSH DIAGRAM
2015
BASUDEV BARAL
REGD NO - 1311106007
MASTER INSCIENCE( APPLIED CHEMISTRY)
COLLEGE OF ENGINEERINGAND TECHNOLOGY( CET ) | BHUBANESWAR

2. 1
WALSH DIAGRAM
CONTENTS
 INTRODUCTION
 CONCEPTS OF WALSH DIAGRAM
 APPLICATION IN TRIATOMIC MOLECULES
[IN AH₂ TYPE OF MOLECULES(BeH₂,BH₂,H₂O)]
INTRODUCTION
Arthur DonaldWalsh FRS The introducer of walsh diagram (8 August1916-23 April1977) was
a British chemist, professor of chemistry atthe University of Dundee . He was elected FRS in
1964. Hewas educated at Loughborough Grammar School.
Walsh diagrams werefirstintroduced in a series of ten papers in one issueof
the Journalof the Chemical Society . Here, he aimed to rationalizethe shapes adopted by
polyatomic molecules in the ground stateas well as in excited states, by applying theoretical
contributions made by Mulliken .
CONCEPTS
Normally we explain the experimentally observed
geometries of molecules by certain devised rules and concepts
such as VSEPR theory , hybridisation , etc . But Walsh actually
Calculated the energies of molecular orbitals of a reference
Geometry and its several distortion for simple tri atomic molecules .
he correctly predicted the actual geometries of a number of simple tri atomic molecules like
H⁺3 , H₂O , BeH₂etc by plotting a graph between the calculated energies of molecular orbitals
of reference geometry and those of the distorted geometries of a molecule vs the distortion
parameter i.e, bond angle.
The position of the minimum energy of filled molecular orbitals in the graph indicates the most
stable geometry of the molecule . Such graphs are known as “WALSH DIAGRAM”

3. 2
 Here there are three tri atomic molecules we take in example BeH2,BH2,H2O , the
number of H atoms presentis 2 , let them Ha , Hb . thus the outer shell of these atoms
are 1sHa , 1sHb .
 In caseof Be , B , O the outer mostshell are2s , 2p .
 Here ,
2s has one orbital
2p has three orbital ( px, py , pz) .
 So total of 6 numbers of outer most orbitals are presenthere namely
1sHa , 1sHb , 2s , 2px, 2py , 2pz .
 6 atomic orbitals combines to form6 molecular orbitals out of which ,
two BMOs = 2
g
,1
u
two ABMOs = 1
u
two areNBMOs = 3
g ,
2
u
 The electrons are filling in the orbitals on account of the lowestenergy of the orbitals .
 So the orbitals with lowestenergy filled first.
 Atomic orbitals represents with a wavefunction related to Hamiltonian operator ,
Ψ = C1 1sHa+ C2 1sHb+ C3 2sH + C4 2pxA + C5 2pyA +C6 2pzA
FOR BeH2MOLECULE
For linear structureAngle HAH = 180⁰

4. 3
Electronic configuration is (2
g
)² (1
u
)²
So in diagramit corresponds to minimumenergy ,so it is the perfect structure .
For bent structure,angle HAH = 90⁰ or 90⁰-180⁰
electronic configuration are,
(2a₁)² (3a₁)² | (2a₁)² (1b₂)²
Itcorresponds to Emaxso unstable not perfectone .
FOR BH2 MOLECULE
for linear structure angle HAH =180° where configuration is ,
(2
g
)² (1
u
)² (1
u
)¹
here energy is maximum , so unstable not preferred one
for bent structure,angle is 90⁰ or 90⁰-180
electronic configuration is ,
(2a₁)² (3a₁)² (1b₂)¹ | (2a₁)²(1b₂)² (3a₁)¹
Stabilisation & destabilisation of energy(Emin)
the electronic configuration is preferred one .
The angle is HAH= in between 90⁰-180⁰i.e, 131
FOR H2O MOLECULE
FOR linear structure angle HAH = 180⁰
electronic configuration is , (2
g
)² (2
u
)² (1
u
)⁴
This structure correspondsto maximum energy so destabilize and not perfect one
Now for bent structureangleis 90 degree or 90-180 degree.
electronic configuration is ,
(2a₁)² (3a₁)² (1b₂)² (1b₁)² | (2a₁)²(1b₂)² (3a₁)²(1b₁)²
stabilisation& destabilisation constant(Emin.)
The second electronic configuration is preferred ,
angle is HAH = 90⁰-180⁰, very closeto 90⁰ (104⁰.28˝).

5. 4
This same concept can be applied to other species including non-hydride AB
2
and BAC
molecules, HAB and HAAH molecules, tetra atomic hydride molecules (AH
3
), tetra atomic non
hydride molecules (AB), H
2
AB molecules, acetaldehyde, penta atomic molecules (CH3I), hexa
atomic molecules (ethylene), and benzene.
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