14 group VIIA

HI
1.40
μ/(10-30c· m)
b.p./℃
6.37
3.57
2.76
polarity
m.p./℃ *-83.57 -114.18 -86.87 -50.80 mp
* 19.52
-85.05 -66.71 -35.1 bp
-92.3
△ fHm /kJ· mol-1 -271.1
-36.4
-26.5
Polyhalogen cations
Polyhalogen cations, such as Br2+, I2+, Cl3+, Br3+, I3+, Br5+, I5+, and I42+ are well known, and prepared the dihalogens X2 using strong oxidants. In the X2 the removal of a p* electron shortens the bond (increases the bond order to 1.5) in Br2+ to 215 pm (vs 227 pm in Br2) and in I2+ to 258 pm (vs 272 pm in I2)
322 155 3.96
（kJ · mol–1）
Electronegativity
(Pauling)
The Elements
Physical Properties： State
Intermolecular Forces
F2 g
Small
Cl2 g
Br2 l
I2 s
Large
b.p./℃
-188
-34
Interhalogens
The interhalogens are a large group of compounds containing combinations of different halogen atoms, such as ClF3 or I2Cl6. They are all prepared by direct combinations of the elements, with the product distribution controlled by temperature and the relative amounts of the halogens used. In general lower tempertures give lower oxidation states of the central atom, while higher oxidation states are achieved by raising the temperature of the reaction. Other features are: • F is always in the oxidation state of -1 • the highest oxidation states for X reached are Cl < Br < I
• Reaction with H2O： Oxidation：
X2 2H2O 4HX O2
F2 Cl 2 Br2 X2 H2O HXO HX Proportionation： Cl 2 Br2 I 2
K (Cl2 ) 4.210
-4
K (Br2 ) 7.210-9
+ HF
2KMnO4+2KF+10HF+3H2O2
== 2K MnF +8H O+3O
2 6 2
2
SbCl5+5HF K2MnF6+2SbF5
423K
== SbF +5HCl
6
2KSbF5+MnF4 MnF3+1/2F2
Industrial：
electrolysis 2NaCl 2H2O H2 Cl2 2NaOH
Twenty electrons are found on the outer iodines (14 e-) or central iodine (6 e-) centered non-bonding MOs, which may be treated as lone pairs of electrons.
Lab：
metathesis
500OC
NaCl H2SO4 (concentrated ) HCl NaHSO4
2NaCl H2SO4 (c) 2HCl Na 2SO4
•HF metathesis
CaF 2 H2SO4 (c) CaSO 4 2HF
• Redox F2
-
Cl2
Br2
I2
E (X 2 /X ) /V： 2.889 1.360 1.0774 0.5345
X2 oxidant： S X reductant： W Conclusion： W S
Strongest Oxidant: F2，Strongest Reductant Iˉ。
F2+NaOH NaF+OF2↑+H2O
300
>1500 1000 Dec T/℃ 432 Bond E/kJ· mol-1 570 Acidity Weak
stability
366
298
Strong
HX polar，easily dissolvable in H2O. @ 273K，1m3 dissolve 500m3 HCl， HF miscible with H2O. forms azeotropic solution with water
+,
X
In the X3+, the cations are bent, with similar X-X distances as in X2.
The I42+ cation is a “rectangular” dimer of I2+, with I-I distances of 258 and 326 pm
-
12H

MnO2 4H 2I
-
-
Mn I 2 2H2 O
2-
2IO3 5HSO3 I2 2SO4 3HSO4 H2O
Hydrogen Halides
1.Properties
@ Ambient T，colorless, pungent HCl HBr HF
BrO3 5Br- 6H 3Br2 3H2 O
-
-
-
•I2 (s) From seaweed ：

(Reverse Proportionation)
Cl2 2I- I2 2Cl2IO
3
6H 2 O 5Cl 2 ( excess ) I2
10Cl
2
Lab：
MnO2 4HCl MnCl 2 Cl 2 (g) 2H2 O
•Br2(l)
Br2 2Cl oxidant： Cl 2 2Br 23Br2 3CO3 5Br - BrO3 3CO2 (proportionation) Purification：
Polyhalides
I 2 KI KI3
I
3
linear
I
I
I


-
Molecular Orbital Theory – I3-
I
I ---- I
The linear I3- molecule, with D∞h symmetry, is an example of 3c-2e bonding. I3- has 22 valence electrons and all but one of the MOs are filled (only the su* orbital is empty). A partial MO diagram, with only the interactions of the Xe 5pz orbital and the LGOs derived from the F 2pz orbitals (su and sg) shown, may be constructed to illustrate the 3c-2e bonding.
Halogens
Fluorine, Chlorine, Bromine, Iodine, Astatine
General Properties
Symbol
Electronic Configuration
Major Oxidation Number Electron Affinity/ (kJ · mol–1 )
HF in solid state:
in dilute solution：
HF H++F－ HF2－ Kaθ = 6.6×10–4 Kaθ = 5
F–+HF
in not-so-dilute solution, HF exists as dimer (HF)2： H 2 F2 H++HF2－
HF reacts with SiO2 and silicates, etching glass
K (I2 ) 2.010-13
The majority exists as elements in aqueous solutions
Preparation of the Elements： (Oxidation)
•F2 (g) Electrolysis： •Cl2 (g)