VSEPR
Lecture G Summary
Bonding explains shapes of molecules
VSEPR valence shell electron pair repulsion simple theory that successfully
= =
the
predicts shape of molecules assumes shape is determined by
+
electron-electronrepulsions .
Sidgwick and Powell (1948) then extended by
Gillespie and Nyholm .
Assumptions :
Atoms in molecule bound by
bondinglone
·
a
pairs
Electron pairs not involved in
bonding are pairs
·
Bonding and lone
pairs arrange
to minimise their interaction ase repelled by electrostatic
·
force and the Pauli principle (electrons seek to
get away from each other) .
Lone pairs occupy space than bonding pairs
·
more
Double bonds occupy space than
more
single bonds
·
Methane Letrahedral. 109 bond
angle
:
He pairs
4 -or
from each other
repelling each other ,
trying to get as
far away
possible
↓
as .
G
repulsions Shape determined by
get
e to
.
trying away
from each other
H S
H 1098
Ammonia :
pyramidal
00
""" +
,Shapes of molecules
:
2 e
pairs
= linear 1800 ) 18
3 c
·
171200
1208
pairs % X
=
↳ pairs .0g
I
3 pairs =
trigonal pyramidal
-
17
G pairs = octahedron
·
7
pairs =
pentagonal bipyramid ·
VSEPR Recipe
·
Draw a LewisStructure centered on atom of interest
Assign to central atom
charge
·
any
·
Determine number of valence shell electrons around central atom.
·
Determine number of double and triple bonds
single
4 6 c
, (2 , ,
domains
Find
domains/regions
-
number of a
·
Assign geometry and +lone
bonding
·
pairs .
Betz
Be 2e
Bett
=
:
Be-f
2
pairs
2 + Be = F linear
~
1800
, BCIz Ch
B Se
B
=
I
B-C B) 1200
&
·
Y
Ch
: pairs a
PT j
J P :
Se F
]
21
--
J P =
- =
6 x 12 1
...
P
· PT
-ve = 12 E
/
I
The -> 6 pairs
F
J
F
Multiple Bonds
·
Determine connectivity .
·
Electron count (valence shell e from bonds) +
·
Where each e is (domains lone pairs) +
50%
S =
Ge 2 Ze domain
&
. k
x
2xle
·
S J
-
:
1 x 4 dom in A
0 3 : S
0 1 x lone
pair
:
based on tetrahedral :
-
Trigonal bipyramidal
CLI ,
asie
,
Clie 1 eq .
-
4
2: pairsequatoriasite
.
Y
Lecture G Summary
Bonding explains shapes of molecules
VSEPR valence shell electron pair repulsion simple theory that successfully
= =
the
predicts shape of molecules assumes shape is determined by
+
electron-electronrepulsions .
Sidgwick and Powell (1948) then extended by
Gillespie and Nyholm .
Assumptions :
Atoms in molecule bound by
bondinglone
·
a
pairs
Electron pairs not involved in
bonding are pairs
·
Bonding and lone
pairs arrange
to minimise their interaction ase repelled by electrostatic
·
force and the Pauli principle (electrons seek to
get away from each other) .
Lone pairs occupy space than bonding pairs
·
more
Double bonds occupy space than
more
single bonds
·
Methane Letrahedral. 109 bond
angle
:
He pairs
4 -or
from each other
repelling each other ,
trying to get as
far away
possible
↓
as .
G
repulsions Shape determined by
get
e to
.
trying away
from each other
H S
H 1098
Ammonia :
pyramidal
00
""" +
,Shapes of molecules
:
2 e
pairs
= linear 1800 ) 18
3 c
·
171200
1208
pairs % X
=
↳ pairs .0g
I
3 pairs =
trigonal pyramidal
-
17
G pairs = octahedron
·
7
pairs =
pentagonal bipyramid ·
VSEPR Recipe
·
Draw a LewisStructure centered on atom of interest
Assign to central atom
charge
·
any
·
Determine number of valence shell electrons around central atom.
·
Determine number of double and triple bonds
single
4 6 c
, (2 , ,
domains
Find
domains/regions
-
number of a
·
Assign geometry and +lone
bonding
·
pairs .
Betz
Be 2e
Bett
=
:
Be-f
2
pairs
2 + Be = F linear
~
1800
, BCIz Ch
B Se
B
=
I
B-C B) 1200
&
·
Y
Ch
: pairs a
PT j
J P :
Se F
]
21
--
J P =
- =
6 x 12 1
...
P
· PT
-ve = 12 E
/
I
The -> 6 pairs
F
J
F
Multiple Bonds
·
Determine connectivity .
·
Electron count (valence shell e from bonds) +
·
Where each e is (domains lone pairs) +
50%
S =
Ge 2 Ze domain
&
. k
x
2xle
·
S J
-
:
1 x 4 dom in A
0 3 : S
0 1 x lone
pair
:
based on tetrahedral :
-
Trigonal bipyramidal
CLI ,
asie
,
Clie 1 eq .
-
4
2: pairsequatoriasite
.
Y
