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 XX bond energy 155 242 193 151 Reduction potential 2.87 1.36 1.07 0.54 X2 + 2e = 2X(aq) Properties vary smoothly down group, but F is “special”

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

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

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.

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).

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: 2Cl  Cl2(g) + 2e 2H2O + 2Cl  H2(g) + Cl2(g) + 2OH 2Na+ + 2OH (=2NaOH) is left behind.

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?

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).

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 NaOClO3H2O sodium chlorite bleach NaOClO2 sodium chlorate oxidizing agent NaOClO3 sodium perchlorate oxidizing agent

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.

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 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.

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.

Chemistry of Noble Gases Xe 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