资源简介

(共63张PPT)
Halogens group 17
Fluorine, Chlorine, Bromine, Iodine, Astatine
Symbol F Cl Br I
Electronic Configuration 2s22p5 3s23p5 4s24p5 5s25p5
Major Oxidation Number –1,0 – 1,0,+1,+3,
+4,+5,+7 – 1,0,+1,+3,
+5,+7 – 1,0,+1,+3,
+5,+7
Electron Affinity/
(kJ ·mol–1 ) 322 348.7 324.5 295
Dissociation Energy of X2/
（kJ ·mol–1） 155 240 190 149
Electronegativity (Pauling) 3.96 3.16 2.96 2.66
General Properties
Physical Properties：
State
g g l s
b.p./℃
-188 -34 59 185
m.p. /℃
-220 -102 -7 114
Color
Pale Yellowish Brown Purple
Yellow Green
Intermolecular
Forces
Small
Large
F2 Cl2 Br2 I2
The Elements
F2 Cl2 Br2 I2
X2 oxidant：
S
W
X- reductant：
W
S
Redox
Strongest Oxidant: F2，Strongest Reductant Iˉ。
Chemical Properties of the Halogens
2.889
1.360
1.0774
0.5345
：
/V
)
/X
X
(
2
-
Conclusion：
F2+NaOH NaF+OF2↑+H2O
（CN)2+2NaOH→NaCN+NaOCN+H2O
Cl2+2NaOH NaCl+NaClO+H2O
Br2+NaOH
50 oC NaBr+NaBrO3+H2O
0 oC NaBr+NaBrO+H2O
3I2+6NaOH→5NaI+NaIO3+3H2O
>80oC
3Cl2+6NaOH 5NaCl +NaClO3+ 3H2O
Proportionation：
The majority exists as elements in aqueous solutions
Reaction with H2O：
Oxidation：
2KMnO4+2KF+10HF+3H2O2 == 2K2MnF6+8H2O+3O2
SbCl5+5HF == SbF6+5HCl
K2MnF6+2SbF5 423K 2KSbF5+MnF4
MnF3+1/2F2
(Oxidation)
F2 (g) Electrolysis：
Cl2 (g)
Preparation of the Elements：
+
HF
Lab：
Industrial：
Br2(l)
oxidant：
(Reverse Proportionation)
I2 (s)
From seaweed ：
Purification：
+
-
-
+
+
+
+
12H
10Cl
2IO
I2
)
(
5Cl
O
6H
3
2
2
excess
O
2H
I
Mn
2I
4H
MnO
2
2
2
2
+
+
+
+
+
+
-
@ Ambient T，colorless, pungent
HF
HCl
HBr
HI
Dec T/℃
>1500
1000
300
Bond E/kJ·mol-1
570
432
366
298
Acidity
Weak
Strong
polarity
bp
stability
mp
*-83.57
-114.18
-86.87
-50.80
m.p./℃
* 19.52
-85.05
-66.71
-35.1
b.p./℃
6.37
3.57
2.76
1.40
μ/(10-30c·m)
Hydrogen Halides
-271.1
-92.3
-36.4
-26.5
/kJ·mol-1
1.Properties
in dilute solution：
in not-so-dilute solution, HF exists as dimer (HF)2：
H2F2
H++HF2－
F–+HF
HF
H++F－
HF2－
Kaθ = 6.6×10–4
Kaθ = 5
SiO2 +4HF == 2H2O+SiF4 ↑
CaSiO3+6HF == CaF2+3H2O+SiF4↑
HF reacts with SiO2 and silicates, etching glass
SiF62- in aqueous solution
HX polar，easily dissolvable in H2O. @ 273K，1m3 dissolve 500m3 HCl，HF miscible with H2O.
forms azeotropic solution with water
HF in solid state:
HCl
HF
metathesis
metathesis
Industrial：
Lab：
2.Preparation of hydrogen halides
Hydrolysis of halides
HBr & HI
(X=Br,I)
No metathesis
Actual
Metathesis with other acid
Intermolecular Forces: Dispersion Force
non-polar
Easily dissolvable in organic solvents, not much in H2O
I2 easily dissolvable in KI、HI and aqueous solution of other iodide solution：
I2 ＋ I－ I3－ K ＝725
I3－ [(I2)n(I－)]
-
3
I
linear
-
Polyhalides
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.
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.
The remaining 2 electrons are found in bonding su MO, such that I3- has a bond order of and the bonding may be described as 3c-2e bonding.
Note that I3- is isoelectronic with XeF2, one of the few known rare gas compounds
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)
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
X
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
the highest oxidation states are achieved in combination with fluorine
Interhalogens
Interhalogens
The interhalogens tend to be good oxidizing agents, and most are fluorides. These interhalogens, XFn, are good fluorinating agents.
UF4(s) + ClF3(g) UF6(s) + ClF(g)
The highest oxidation state for the central atom X is found in IF7, as the smaller halogens are not large enough to accommodate more than 5 fluorides, with the large interfluoride lone pair repulsions.
While ClF3 and BrF3 are T-shaped, ICl3 dimerizes to form I2Cl6
In I2Cl6 each I atom has two “axial” lone pairs, such that the molecule is planar, with D2h symmetry
Hypofluorous acid HOF
For fluorine, the only known oxoacid is hypofluorous acid, HOF, in which fluorine is in the +1 oxidation state. It can be made by passing F2 gas over ice at -40 °C and collecting the HOF gas which condenses. It decomposes at room temperature to form HF and O2
F2 + H2O HOF + HF
Instead of ionizing in water, it reacts with water to form hydrogen peroxide and hydrogen fluoride.
HOF + H2O H2O2 + HF
Halogen oxoacids
Oxoacids of chlorine Oxoacids of bromine Oxoacids of iodine
Hypochlorous acid (Cl +1) HOCl Hypobromous acid HOBr Hypoiodous acid HOI
Chlorous acid
(Cl +3) HOClO (HClO2)
Chloric acid
(Cl +5) HOClO2 (HClO3) Bromic acid HOBrO2 (HBrO3) Iodic acid HOIO2 (HIO3)
Perchloric acid
(Cl +7) HOClO3 (HClO4) Perbromic acid HOBrO3 (HBrO4) Periodic acid
Ortho-periodic acid HOIO3 (HIO4)
(HO)5IO
(H5IO6)
Hypohalous acids HOX
HOX HOCl HOBr HOI
pKa 4.53 8.69 10.64
The hypohalous acids (HOX) are known for each halogen (HOF described before) and for X = Cl, Br, and I, can be made by the reaction of the halogen with mercuric oxide.
2 X2 + 3 HgO + H2O Hg3O2X2 + 2 HOX
These acids cannot be isolated, but in aqueous solution they behave as weak acids.
hypohalorous acid and hypohalogenite
HClO HBrO HIO
acidity↓
Oxidizing power↓
stability：
stable
less stable
2.8×10-5 2.6×10-9 2.4×10-11
1.495 1.341 0.983
)/V
X
/
XO
(
-
-
Hypohalite anions
Hypochlorite salts can be isolated with cations such as Na+, K+, and Ca2+ . Sodium hypochlorite, NaOCl, is a bleaching agent (pool bleach) and disinfectant
Hypohalites are powerful oxidizing agents (Eo = 1.61 V for HOCl, 1.58 V for HOBr, and 1.44 for HOI)
2 HOX + 2e- + 2 H+ X2 + 2 H2O
Hypohalite anions
The hypohalites are all unstable with respect to disproportionation. At room temperature, this process is slow for HOCl, fast for HOBr, and very fast for HOI. The products are the halate anions (XO3-) and the halide (X-)
3 NaOCl NaClO3 + 2 NaCl
Why are the hypohalites unstable with respect to disproportionation We can look at the thermodynamics of the process, using the reduction potentials for the various halogen species in solution.
Important RXNs：
bleaching powder
Halogen oxoacids and oxoanions
Hypohalite disproportionation:
3 OX- XO3- + 2 X-
(X +1) (X +5) (X -1)
which is made up of:
OX- + 2 H2O XO3- + 4 e- + 4H+
OX- + 2 H+ + 2 e- 2 X- + H2O
Halic acids, HXO3
The halic acids, HXO3, are strong acids (pKa < 0 for X = Cl and Br, and 0.77 for X = I), but only HIO3 can be isolated, as a stable white solid. The halic acids are prepared by:
Ba(XO3)2 + H2SO4 BaSO4 + 2 HXO3 (X = Cl or Br)
I2O5 + H2O 2 HIO3
The HIO3 is stabilized in the solid state by considerable H bonding
Halic Acids and Halates
Halic acid： HClO3 HBrO3 HIO3
acidity：↓ S S M
1.458 1.513 1.209
Cmax Obtained：
40% 50% crystal
Stability：
high
low
)/V
X
/
XO
(
2
-
3
Halate anions
The halate anions, XO3-, have a number of uses:
ClO3- strong oxidizing agent, used as a weedkiller and in the manufacturing of ClO2, and in fireworks and safety matches
BrO3- and IO3- are used in volumetric analyses
IO3- + 5 I- + 6 H+ 3 I2 + 3 H2O
Potassium chlorate
The gritty material on the side of a match-box is coated with red phosphorus. The match-head contains potassium chlorate and some red colouring. When the match-head rubs against the box, friction ignites the mixture of phosphorus and potassium chlorate.
Potassium chlorate
By separating the strong oxidizer (potassium chlorate) from the reducer (phosphorus) the matches are prevented from igniting spontaneously.
Perhalic Acids and Perhalates
HClO4 HBrO4 H5IO6
Acidity：↓strongest strong weak
1.226 1.763 1.60
All are strong oxidizing agents, stable pure form
4
-
=
)
10
4
.
4
(
×
HIO4
)/V
/XO
(XO
3
4
-
-
O
40% max solution
May obtainsolid
1.495 1.55 1.45 1.409
Oxidizing power ↓(except HClO2)
Oxo acids of chlorine
HClO HClO2 HClO3 HClO4
Acidity：
Stability：
/V
)
X
/
(
-
ox
low low relatively S Stable
Oxo acids and their sodium salts
acid Stability & acidity oxidant salt stability Oxidant basicity
+1 HOCl 　　
NaClO 　
　
　 　　
　　
+3 HOCl2 NaClO2
+5 HOCl3 NaClO3
+7 HOCl4 NaClO4
stabilty
oxidant
Important RXN：
Periodic acids and anions
The equilibria between different forms of periodic acids an anions is quite complex:
H3IO62- + H+ HIO4- + 2H2O
2 H3IO62- 2 HIO52- + 2 H2O
2 HIO52- H2I2O104- I2O94- + H2O
Structure of oxoacids
Identification of I-、Br- mixture
THE NOBLE GASES GROUP 18
helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn)
Rare Gases, Inert Gases
Group 8A – The Noble Gases
Discovery
He: 1868 by P Janssen & J N Lockyer discovered while looking at the chromosphere of the Sun.
Ar: 1895 by Lord Rayleigh & W Ramsay found air was mixed with another gas: argon. During his search for argon, Ramsay also managed to isolate helium for the first time while heating cleveite, a mineral.
krypton, neon, and xenon: 1898 by Ramsay by fractional distillation of liquid air.
Radon: 1898 by F E Dorn from radium emanation (镭射气).
Uses
Liquid helium is used to cool the superconducting magnets in modern MRI scanners
15,000-watt xenon short-arc lamp used in IMAX projectors
Discharge Color
Gas 2004 price (USD/m3)
Helium (industrial grade) 4.20–4.90
Helium (laboratory grade) 22.30–44.90
Argon 2.70–8.50
Neon 60–120
Krypton 400–500
Xenon 4000–5000
Prices
Radon
Radon is radioactive, and is formed in rocks and soil by the radioactive decay of uranium and thorium. 222Rn can infiltrate the air in basements. Since it is gaseous, it is breathed into the lungs where it undergoes radioactive decay, bombarding lung tissue with alpha and beta particles. These particles disrupt living cells and can initiate lung cancer.

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