Halogens - Group VII
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Transcript of Halogens - Group VII
Halogens - Group VII
Property F Cl Br I Atomic radius (Å) 0.72 1.00 1.15 1.40
Electron affinity 332 349 325 295(kJ/mol) Electronegativity 4.0 3.2 3.0 2.7
XX bond energy 155 242 193 151(kJ/mol)
Reduction potential 2.87 1.36 1.07 0.54X2 + 2e = 2X(aq)
Properties vary smoothly down group, but F is “special”
Electronegative high ionization energies high electron affinities
Sources in nature:F fluorspar CaF2
Cl, Br, I Seawater
Source of diatomic (elemental) formF, Cl electrolysis Br, I displacement reactions
Oxidation StatesF -1Cl, Br, I -1 most common
+1, +3, +5, +7 in combo with O, F
Halogens
FluorineProduced 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
USES OF FLUORINE
1) 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) TeflonF2C=CF2 -CF2 – CF2 – CF2 – CF2-
Non-sticky surface. Resists high temperatures.
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) HFSource:CaF2(s) + H2SO4(l) 2HF(g) + CaSO4(s)
HF reacts with glass – used to etch glass to put on “frosty” designs.
GlassSiO2(s) + 4HF(l) SiF4(g) + 2H2O(l)
SiF4 + 2HF H2SiF6(aq)________________________________ SiO2(s) + 6HF(l) H2SiF6(aq) + 2H2O(l).
Chlorine
Yellow-green diatomic gas at 298KPoisonous, corrosive (good oxidizing agent)
Source: electroysis of NaCl (aqueous or molten)
Cathode: 2H2O + 2e H2(g) + 2OH
Anode: 2Cl Cl2(g) + 2e
2H2O + 2Cl H2(g) + Cl2(g) + 2OH
2Na+ + 2OH (=2NaOH) is left behind.
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 hypochlorite5% solution = Chlorox bleachSwimming pool disinfectant
Don’t add acid to bleach!! Why?
Chlorine:Uses
I2 solid, gray, purple crystals
Source: seawater, salt deposits
USEessential for the human body(thyroid gland) Lack of I = causes goiter KI is routinely added to table salt (iodized salt).
Iodine
INTERHALOGEN COMPOUNDS
1:1 ICl, BrCl
1:3 ClF3, ICl3
1:5 BrF5, IF5 Only Br & I as central atoms
1:7 IF7 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
OXYACIDS and OXYANIONS OF HALOGENS
HXOn (X = Cl, Br, I, but not F)All are strong oxidizing agents
Salts:
NaOCl sodium hypochlorite bleach
NaOClO3H2O sodium chlorite bleach
NaOClO2 sodium chlorate oxidizing agent
NaOClO3 sodium perchlorate oxidizing agent
Properties: low electron affinitydo not readily form compounds.
Source of Ne, Ar, Kr, Xeliquefy airseparate through fractional distillation
Source of Heproduct of radioactive decay found in large subterranean reservoirs also occupied by natural gas.
NOBLE GASESGroup 8 (VIII)
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.
USES OF INERT GASESHelium:
1) Inert gas blanket for arc welding.
2) 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.
ARGON - 1% of air1) 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.
NEONNe 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.
RADONRadon is dangerous because of its radioactivity.
Chemistry of Noble GasesXe has IE =1176kJ IE of O2 = 1171kJ
Xe makes compounds with O, F, (N, H, Au,…)
Xe + n F2 XeF2 +2 oxidation
XeF4 +4 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