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