1 Covalent Bonding: Molecular Geometry Hybridization of Atomic Orbitals Molecular Orbitals.
Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons...
-
Upload
gerard-wade -
Category
Documents
-
view
226 -
download
3
Transcript of Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons...
![Page 1: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/1.jpg)
Valence Bond Theory
Developed by Linus Pauling
![Page 2: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/2.jpg)
Overlap of Atomic Orbitals
The sharing of electrons between atoms is viewed as an overlap of atomic orbitals of the bonding atoms.
![Page 3: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/3.jpg)
The overlap of orbitals
![Page 4: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/4.jpg)
When H – H distance = 74 pm,
Repulsion = Attraction
strongest bond
optimal overlap
lowest energy
74 pm
![Page 5: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/5.jpg)
At H – H distance > 74 pm,
Repulsion < Attraction
weaker bond
too little overlap
atoms come closer
74 pm
> 74 pm
![Page 6: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/6.jpg)
At H – H distance < 74 pm,
Repulsion > Attraction
weaker bond
too much overlap
atoms get further apart74
pm
< 74 pm
![Page 7: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/7.jpg)
Because of orbital overlap, the bonding electrons localize in the region between the bonding nuclei such that
There is a high probability of finding the electrons in the region between the bonding nuclei.
![Page 8: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/8.jpg)
Overlap of two Overlap of two half-filledhalf-filled orbitals orbitals leads to the formation of a covalent leads to the formation of a covalent bond.bond.
1s
1s
1s-1s overlap gives a H – H single bond
![Page 9: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/9.jpg)
F
2s 2p
1s
H
The 1s-2p overlap gives a H – F single bond
![Page 10: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/10.jpg)
Non-bonding Non-bonding electronselectrons
F
2s 2p
1s
H
![Page 11: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/11.jpg)
F
2s 2p
The 2p-2p overlap gives a F – F single bond
F
2s 2p
![Page 12: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/12.jpg)
F
2s 2p
Non-bonding electrons
F
2s 2p
Each F atom has three pairs of non-bonding electrons.
F F
![Page 13: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/13.jpg)
Q.23 Identify the non-bonding electrons in O2 molecules.
Two 2p-2p overlaps give a O=O double bond
O
2s 2p
O
2s 2p
![Page 14: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/14.jpg)
Q.23 Identify the non-bonding electrons in O2 molecules.
Each O atom has two pairs of non-bonding electrons.
O
2s 2p
O
2s 2p
Non-bonding electrons
O O
![Page 15: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/15.jpg)
Overlap of anOverlap of an empty orbitalempty orbital with awith a fully-fully-filled orbitalfilled orbital leads to the formation of aleads to the formation of a co-ordinate covalent bondco-ordinate covalent bond oror dative bonddative bond
![Page 16: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/16.jpg)
O
O
O
Represented by an arrow pointing from the electron pair donor to the electron pair acceptor.
N
H
H
H
H++ N
H
H
H
H
![Page 17: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/17.jpg)
N
O
O O
![Page 18: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/18.jpg)
F3B NH3+
F3B NH3
![Page 19: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/19.jpg)
Interpretation of the Interpretation of the Formation of Covalent Formation of Covalent
Bonds in terms ofBonds in terms of Valence Valence Bond TheoryBond Theory
![Page 20: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/20.jpg)
(a) NH(a) NH44++
N H
H
H
H
By Lewis model, the structure is
4 single bonds are formed,
one of them is a dative bond.
![Page 21: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/21.jpg)
By VB Theory,
Three 2p-1s(half-filled) overlaps lead to the formation of three N – H single bonds.
N
2s 2p
3H H+
1s 1s
N
H
H
H
![Page 22: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/22.jpg)
By VB Theory,
One 2s(fully-filled)-1s(vacant) overlap leads to the formation of one N H dative bond.
N
2s 2p
3H H+
1s 1s
N
H
H
H
H++ N
H
H
H
H
![Page 23: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/23.jpg)
(b) HCN
By Lewis model, the structure is H-CN one H-C single bond and
one CN triple bond.
![Page 24: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/24.jpg)
By VB Theory,By VB Theory,
C
Only 2 single bonds can be formed. Promotion of a 2s electron to a 2p
orbital.
2s 2p
C*
2s 2p
![Page 25: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/25.jpg)
The overlap of one orbital (?) of C* with an 1s orbital of H gives the C-H single bond. Overlaps of three orbitals (???) of C* with three 2p orbitals of N give the CN triple bond.
C*
2s 2p
N
2s 2p
H
1s
![Page 26: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/26.jpg)
The 2s electrons on N are non-bonding electrons.
The energy released by forming a stronger triple bond outweighs the energy required
for promoting an electron from a 2s orbital to a 2p orbital.
C*
2s 2p
N
2s 2p
H
1s
H C N
![Page 27: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/27.jpg)
(c) SO2
By Lewis model, the three possible structures are
OS=O, O=SO, O=S=O
Most stable no separation of opposite formal
charges.
![Page 28: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/28.jpg)
By VB Theory,
Only two single bonds can be formed. One 3p electron has to be promoted to a 3d orbital.
Expansion of Octet.
S
3s 3p
![Page 29: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/29.jpg)
By VB Theory,
S
3s 3p
S*
3s 3p
3d
octet expansion
![Page 30: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/30.jpg)
Overlaps of two half-filled orbitals (??) of S* with two half-filled 2p orbitals of an oxygen atom give a S=O double bond.
A total of two S=O bonds are formed with two O atoms
2O
2s 2p
S*
3s 3p
3d
O
S
O
![Page 31: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/31.jpg)
Non-bonding electrons :
S* 3s2 ;
O 2s2 and 2p2
2O
2s 2p
S*
3s 3p
3d
O
S
O
![Page 32: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/32.jpg)
The energy released by forming of two stronger double bonds outweighs the energy required for promoting an electron from a 3p orbital to a 3d orbital.
S
3s 3p
S*
3s 3p
3d
octet expansion
![Page 33: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/33.jpg)
The Concept of The Concept of ResonanceResonance
According to VB theory, the two less stable structures of SO2,
OS=O and O=SO do ‘exist’.
Each of these structures contributes in certain extent to the real structure of SO2.
![Page 34: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/34.jpg)
If represents the wave function of the real structure of SO2 molecules, then
2SO
OSOOSOOSOSO cba 2
where
OSO OSO OSO
are the wave functions of the three possible structures and
a > b = c > 0
![Page 35: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/35.jpg)
In other words, the real structure of SO2 is the resonance hydrid of the three possible structures.
O=S=O OS=O O=SO
More contribution
Less contribution
![Page 36: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/36.jpg)
Q.24
S
3s 3p
O
2s 2p O*
2s 2p
A S=O double bond is formed by 3p(half-filled)-2p(half-filled) overlaps between S and O.
O=SO
![Page 37: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/37.jpg)
Q.24
S
3s 3p
O
2s 2p O*
2s 2p
O=SO
A OS dative bond is formed by 3p(fully-filled)-2p(empty) overlap between S and O*
![Page 38: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/38.jpg)
Q.24
S
3s 3p
O
2s 2p O*
2s 2p
O=SO
Formation of dative bond is not favourable because the two unpaired 2p electrons in O are forced to pair up to give O*
![Page 39: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/39.jpg)
(d) SF2, SF4, SF6
Most stable Lewis
Structure
SF6SF4SF2Molecule
F-S-F S
F
F
F
F S
F
F
F
F
F
F
6B
![Page 40: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/40.jpg)
By VB Theory,
Only two S-F single bonds can be formed by 3p-2p overlaps between one S atom and two F atoms
SF2 is formed.
S
3s 3p F
2s 2p
F-S-F
![Page 41: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/41.jpg)
By VB Theory,
To form four S-F single bonds in SF4, a 3p electron in S has to be promoted to a 3d orbital.
S
3s 3p F
2s 2p
S*
3s 3p
3d
![Page 42: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/42.jpg)
By VB Theory,
To form six S-F single bonds in SF6, a 3s electron in S* has to be promoted to a 3d orbital.
S
3s 3p F
2s 2p
S**
3s 3p
3d
![Page 43: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/43.jpg)
By VB Theory,
S
3s 3p
S**
3s 3p
3d
The energy released by forming more single bonds outweighs the energy required for promoting 3s and 3p electrons to 3d orbitals.
![Page 44: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/44.jpg)
Q.25
Most stable Lewis
Structure
XeF6XeF4XeF2Molecule
F-Xe-F Xe
F
F
F
F Xe
F
F
F
F
F
F
![Page 45: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/45.jpg)
By VB Theory,
To form two Xe-F bonds in XeF2, a 5p electron in Xe has to be promoted to a 5d orbital.
Xe
5s 5p F
2s 2p
Xe*
5s 5p
5d
![Page 46: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/46.jpg)
By VB Theory,
To form four Xe-F bonds in XeF4, a 5p electron in Xe* has to be promoted to a 5d orbital.
Xe*
5s 5p
5d
Xe**
5s 5p
5d
![Page 47: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/47.jpg)
By VB Theory,
To form six Xe-F bonds in XeF6, a 5p electron in Xe** has to be promoted to a 5d orbital.
Xe**
5s 5p
5d
Xe***
5s 5p
5d
![Page 48: Valence Bond Theory Developed by Linus Pauling. Overlap of Atomic Orbitals The sharing of electrons between atoms is viewed as an overlap of atomic orbitals.](https://reader030.fdocuments.net/reader030/viewer/2022032612/56649ec55503460f94bd0bc0/html5/thumbnails/48.jpg)
By VB Theory,
Xe**
5s 5p
5d
Xe***
5s 5p
5d
The energy released by forming more single bonds outweighs the energy required for promoting 5p electrons to 5d orbitals.