Group 7A Elements PPT

Group 7A Elements PPT - General Properties Group 17(VII...

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Unformatted text preview: General Properties Group 17 (VII) Elements: Halogens • The most electronegative group - withdrawing ability (enhances Bronsted acidity), electronegativity decreases down the group • Boiling points and melting points are relatively low and increase down the group F Electronegative, Reactive and Here to Stay… Stay… Cl Br I At Electronegativity 4.0 3.0 2.8 2.5 2.2 Melting point / deg C -220 -101 -7.2 114 302 Boiling point/deg C -188 -34.7 58.8 184 • Colors include nearly colorless-yellow (F), colorlessyellow-green (Cl), red-brown (Br), and purple yellow(Cl), red(I) • “That’s color. That’s fun.” ~Bob That’ That’ fun.” States of Halogens At room temperature, fluorine is in gaseous form At room At temperature, Bromine is in liquid form . At room temperature, chlorine is in gaseous form At room temperature, Iodine is in solid form Intermolecular forces are primarily responsible for the differences in the states of the elements. The larger more polarizable atoms induce dipole moments more easily and are less volatile. More General Properties • Covalent and ionic radius: slightly lower than Group 16, decreases down group • First ionization energy, highest except for Noble gases, decreases down the group • Electron affinity, highest vs. other groups, Cl has highest Ea, but generally decreases down group. F Cl Br I At Covalent radius/pm 72 99 114 133 Ionic radius /pm 117 167 182 206 First ionization energy (kJ/mol--1) 15680 1250 1140 1008 Electron affinity (kJ/mol-1) (kJ/mol 334 355 325 295 140 270 1 Fluorine is Special General Reactivity • Most reactive nonmetal group • Bond dissociation enthalpy trends • Oxidation numbers are typically -1, can have +1, +3, +5, & +7 oxidation states • Note: F exception Bond Dissociation Enthalpy (Shriver & Atkins Fig. 16.5) 300 Bo n d Dis. enth alp y (kJ/m o l) 250 243 193 200 159 151 150 100 50 0 F2 Cl2 Br2 Halogens Hydrogen Fluoride Fun • • • • Less acidic than other hydrogen halides Volatile liquid vs. gas (Higher BP) High electrical conductivity Hydrogen Bonding: Linear (No 3D Network which exists in H20) • Excellent non-aqueous solvent non• Very Dangerous – Readily absorbs through skin: toxic and corrosive I2 • The most electronegative element… element… ever… ever… • The strongest oxidizing agent besides Oxygen. Raises cations to high oxidation states. • Fluorine is distinctive: strong Coulombic repulsion, explains lower electron affinity and bond dissociation • Never has positive oxidation state Halogen Gas Formation • All halogen diatomic gases are produced differently… differently… • Bromine gas comes from chemical oxidation of Br - ions in seawater • Fluorine gas isolated from electrolysis of 1:2 molten KF and HF 2 Industrial Applications • Fluorine gas stored in steel or monel metal (Ni/Cu alloy) which forms passivating metal fluoride surface film • Dr. Leland Clark – Perfluorocarbons CH3 H3C C CF 3 CH3 O H2 C F2/He CH F 3C C tert-butyl isobutyl ether CH3 • Grignard Reagents - Mg & Halogens • A powerful synthetic tool to create a variety of polyfunctional heterocycles • Sensitive groups such as nitro, hydroxy and boronic ester. CF3 O F2 C OMe CF OMe N CF 3 Ph N Industrial Applications • Using Halogens in the Combustion of Coal • Halogens react with oxygen free radicals in fluidized bed combustion (FBC). • Greatly increases the CO and hydrocarbon concentrations in the gases when salt halides are added to FBC. - CO CO2 does not occur CO H Ph N Br OMe • Oxycyte - High Oxygen Carrying Capacity, Possible Use as Artificial Blood N + CF3 perfluoro(tert-butyl isobutyl ether) OH O MgCl -120 C CH3 Industrial Applications Br OMe • Professor Ila - Preparation and Reactions of Heteroaryl Organomagnesium Compounds Industrial Applications • Halogens increase NO concentrations because the reaction NO N2O involves free radicals. • I2 is better at decreasing the oxygen free radicals than Cl2 3 Environmental Applications • Volatile organohalogens break down ozone. • Some volatile organohalogens; organohalogens; including methyl chloride, methyl bromide, methyl iodide, chloroform, and bromoform; form highly reactive bromoform; halogen radicals. Environmental Applications Environmental • These volatile organohalogens are produced by marine macroalgae. macroalgae. • It has been discovered that UV light actually catalyzes the production of volatile organohalogens by macroalgae. macroalgae. • The problem is cyclical. 4 ...
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