1. Halogens - Group VII Property F Cl Br I
Atomic radius (Å)
Electron affinity 332 349 325 295
(kJ/mol)
Electronegativity
XX bond energy
Reduction potential
X2 + 2e = 2X(aq)
Properties vary smoothly down group, but F is “special”

2. Halogens Electronegative high ionization energies
high electron affinities
Sources in nature:
F fluorspar CaF2
Cl, Br, I Seawater
Source of diatomic (elemental) form
F, Cl electrolysis
Br, I displacement reactions
Oxidation States
F -1
Cl, Br, I -1 most common
+1, +3, +5, +7 in combo with O, F

3. Fluorine Produced by electrolysis of KHF2
Never has positive oxidation state
Strong oxidizing agent
VERY REACTIVE: reacts with all elements except He, Ne, Ar
Reacts with
-compounds containing H
-glass
-metals
How do you contain it???
In Ni cylinders
Monel: Ni + F2  NiF2

4. USES OF FLUORINE F- is added to toothpaste.
Growing teeth incorporate it as Ca5(PO4)3F which resists tooth decay
2) Freon refrigerants
e.g. CCl3F, CCl2F2 are unreactive and low boiling.
Used in refrigerators, air conditioners, and as propellants in spray cans.
Freons are used less today because they damage the ozone layer.
3) Teflon
F2C=CF2  -CF2 – CF2 – CF2 – CF2-
Non-sticky surface. Resists high temperatures.

5. USES OF FLUORINE CONT. 4) Fluorides of many elements are gases:
e.g. UF6 is used to separate 235U from 238U – they diffuse at different rates.
e.g. SiF4(g) is produced when Si is etched by HF.
5) HF
Source:
CaF2(s) + H2SO4(l)  2HF(g) + CaSO4(s)
HF reacts with glass – used to etch glass to put on “frosty” designs.
Glass
SiO2(s) + 4HF(l)  SiF4(g) + 2H2O(l)
SiF4 + 2HF  H2SiF6(aq)
________________________________
SiO2(s) + 6HF(l)  H2SiF6(aq) + 2H2O(l).

6. Chlorine Yellow-green diatomic gas at 298K
Poisonous, corrosive (good oxidizing agent)
Source:
electroysis of NaCl (aqueous or molten)
Cathode: 2H2O + 2e  H2(g) + 2OH
Anode: Cl  Cl2(g) + 2e
2H2O + 2Cl  H2(g) + Cl2(g) + 2OH
2Na+ + 2OH (=2NaOH) is left behind.

7. 8th ranked industrial chemical
Chlorine:Uses
8th ranked industrial chemical
Main Uses:
production of polyvinyl chloride plastics
Good oxidizing agent:
Cl2 for water purification
Cl2 (g) + 2 OH-(aq)  Cl-(aq) + OCl-(aq) + H2O(l)
Disproportionation (auto oxidation)
NaOCl - sodium hypochlorite
5% solution = Chlorox bleach
Swimming pool disinfectant
Don’t add acid to bleach!! Why?

8. Iodine I2 solid, gray, purple crystals Source: seawater, salt deposits
USE
essential for the human body
(thyroid gland) Lack of I = causes goiter
KI is routinely added to table salt
(iodized salt).

9. INTERHALOGEN COMPOUNDS
1:1 ICl, BrCl
1:3 ClF3, ICl3
1:5 BrF5, IF Only Br & I as central atoms
1:7 IF Only I as central atom
Central atom always bigger and less electronegative
Reaction with water: Oxidation state unchanged
ClF3 + 2 H2O  HClO2 + 3 HF
IF7 + 4 H2O  HIO4 + 7 HF

10. OXYACIDS and OXYANIONS OF HALOGENS
HXOn (X = Cl, Br, I, but not F)
All are strong oxidizing agents
Salts:
NaOCl sodium hypochlorite bleach
NaOClO3H2O sodium chlorite bleach
NaOClO sodium chlorate oxidizing agent
NaOClO sodium perchlorate oxidizing agent

11. NOBLE GASES Group 8 (VIII)
Properties: low electron affinity do not readily form compounds. Source of Ne, Ar, Kr, Xe liquefy air separate through fractional distillation Source of He product of radioactive decay found in large subterranean reservoirs also occupied by natural gas.

12. HELIUM Properties: Gas with a very low boiling point: -268.9°C = 4.2K.
Helium is too light to be held by earth’s gravity. We lose it!
Produced by radioactive decay (a-particle = He nucleus) in uranium and thorium containing minerals.
Found in natural gas wells in Texas and Oklahoma due to geological formations containing U and Th.

13. USES OF INERT GASES Helium:
Inert gas blanket for arc welding.
Diluent for oxygen in breathing gas for divers. It has a very low solubility in water.
3) Liquid helium is used to cool to very low (cryogenic) temperatures.
4) Float blimps.
5) Used in lasers.
6) Very light – vibrates faster in larynx – makes chemistry professors have high squeaky voices like Jacques Cousteau.

14. ARGON - 1% of air NEON RADON
1) Inert gas blanket for welding – heavier than air.
2) Blanketing atmosphere in electric light bulbs – does not react with hot filament, but conducts heat away from it.
3) Used in lasers.
NEON
Ne is used as one of the gases to fill neon-light tubes.
KRYPTON and XENON
Xe and Kr are used as light emitters in flash devices.
RADON
Radon is dangerous because of its radioactivity.

15. Chemistry of Noble Gases
Xe has IE =1176kJ  IE of O2 = 1171kJ
Xe makes compounds with O, F, (N, H, Au,…)
Xe + n F2  XeF oxidation
XeF states
XeF6 +6
XeF6(s) + H2O(l)  XeOF4(l) + 2HF(g)
XeF6(s) + 3H2O(l)  XeO3(l) + 6HF(aq)
KrF2 (can’t make KrF4 or KrF6)
Endohedral complex:
He inside C60 cage
First “compound” made with He: no uses