Greenwood & Earnshaw - University of Tennesseeweb.utk.edu/~adcock00/g531ch17.pdf · 1 Greenwood &...
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1 Greenwood & Earnshaw 2 nd Edition Chapter 17 The Halogens Fluorine, Chlorine, Bromine, Iodine and Astatine Molecular Orbital Diagram – F 2 2s 2s σ* σ σ π σ* π* 2p 2p F F F 2 2s & 2p atomic orbitals are too widely separated in energy to allow significant mixing (hybridization) to occur. Bond Energies for the Halogens, kJ/mol Fluorine bond energies are “anomalous”. The F-F bond is very weak due to lone-pair/lone-pair repulsions (cf. O-O, N-N). Fluorine has tightly held, non-polarizable electrons, the atoms are small and no low-lying “d” atomic orbitals exist. The fluorine lone pairs are strong π-donors to atoms having low-lying empty orbitals. Fluorine forms strong, polar bonds to carbon, hydrogen and many other elements. Fluorine is very electrophilic and strongly oxidizing.
Transcript of Greenwood & Earnshaw - University of Tennesseeweb.utk.edu/~adcock00/g531ch17.pdf · 1 Greenwood &...
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Greenwood & Earnshaw2nd Edition
Chapter 17
The Halogens
Fluorine, Chlorine, Bromine, Iodine and Astatine
Molecular Orbital Diagram – F2
2s 2s
σσσσ*
σσσσ
σσσσ
ππππ
σσσσ*
ππππ*
2p 2p
F F
F2
2s & 2p atomic orbitals are too widely separated in energy to allow significant mixing (hybridization) to occur.
Bond Energies for the Halogens, kJ/mol
Fluorine bond energies are “anomalous”. The F-F bond is very weak due to lone-pair/lone-pair repulsions (cf. O-O, N-N). Fluorine has tightly held, non-polarizable electrons, the atoms are small and no low-lying “d” atomic orbitals exist. The fluorine lone pairs are strong ππππ-donors to atoms having low-lying empty orbitals. Fluorine forms strong, polar bonds to carbon, hydrogen and many other elements. Fluorine is very electrophilic and strongly oxidizing.
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Molecular Orbital Diagram – Cl2, Br2, I2
3s & 3p and higher atomic orbitals are not so widely separated in energy and allow significant mixing (hybridization) to occur.
This mixing causes the inversion of the σσσσ and ππππmolecular orbitals’ energy.
σσσσ
ππππ
σσσσ*ππππ*
3,4,5 p
3, 4,5 s
σσσσ*
σσσσ
3,4,5 s
3,4,5 p
Interhalogens
Br
BrF
F
BrF
F
F
F
IF
F F
F
F
F
BrF
F
F
F
FI
F
F
F
IFF
FF
FF
F
Cs+IF8-
square antiprismatic?
diatomicY is the heavier halogen!
YXY+ -X- +X-YX2
-
X2
YX3YX2+ -X- +X-
YX4-
X2
YX5YX4+ -X- +X-
YX6-
X2
YX7YX6+ -X- +X-
YX8-
FI
F
F F
FBr
F
F F
F
Br FF
F
Trihalide Anions�The heavier halogen is invariably in the center position.
�The anion is linear or near linear. One Deviation is for Br3
- which is 171EEEEmost 176EEEE or higher.
�The bonding is almost certainly 3c-4e bonding.
�The two bonds in YX2 species need not be equivalent and may vary with the cation.
�The bond length is longer than the single bond covalent radii. The formal bond order is 0.5. In BrI2
- the Br-I bond is longer than the I-I bond.
�Iodine forms an extensive set of polyiodine anions: In- n =
odd; In2- n = even, I16
4- . (see page 837).
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Iodine Oxides and Oxoacids of Iodine
OI O
I O
OO
I2O5
183 pm179 pm
195 pm192 pm
178 pm177 pm
139.2EEEE
∆∆∆∆HEEEEf = -158.1 kJI4O9 & I2O4 also known
IHOHO
OHOH
OH
O
ortho-periodic acidH5IO6
189 pm
178 pm
- H2O
-2 H2O
Dimer
Trimer
I
O
OO
O
-178 pm
NaIO4 K3IO5 K5IO6periodate
ortho-periodate
meso-periodate (edge-sharing)
IO O
O
O O
O
O
O
O
I
4-
meso-periodate (face-sharing)
I
O
O O
OO
OH O
O
O
OH
I
4-
I
O
O O
OO
3-178 pm
177 pm
95EEEEI
O
O O
OO
O
5-
185 pm
