24.2 part 3


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24.2 part 3

  1. 1. Other Group 6A elements<br />Selenium is a semi-conductor; poor conductor of electricity in dark, good in light; this makes it useful in photovoltaic cells, also used in photocopying machines<br />Te is rare, and its compounds are toxic<br />
  2. 2. Halogens, Group 7A<br />Do not exist in nature uncombined, but their compounds are abundant; many of their sodium salts (NaF, NaI,NaCl,NaBr) are found in seawater; CaF2 is fluorspar- a mineral<br />All are nonmetals<br />Fluorine and chlorine are gases and yellowish to green; bromine is dark red liquid, iodine is a black solid ( vapors are purple)<br />All are very reactive ( they only need 1e-)<br />
  3. 3. Most are water soluble<br />All hydrogen halides, except HF, form strong acids ( hi ionization)<br />Halogens, Group 7A<br />
  4. 4. Chlorine<br />Chlorine is 10th in the Top 50 list of chemicals produced.<br />It is a yellow, pungent and highly corrosive gas.<br />Cl2 is too reactive to occur free in nature.<br />Chlorine occurs mostly as sodium chloride in salt waters and mineral deposits.<br />Industrial preparation - electrolysis of NaCl.<br />2NaCl (aq)+ 2H2O (l) 2NaOH (aq) + Cl2 (g) + H2 (g)<br />
  5. 5. Chlorine<br />Uses<br />About 70% of all chlorine is used in the chemical industry. In many cases, the final compound does not even contain chlorine.<br />About 20% is used to bleach wood pulp and paper to make it white.<br />Another 5% is used for water treatment.<br />Household bleach is made by allowing chlorine to react with NaOH.<br />Cl2 (aq) + 2NaOH (aq) NaOCl (aq) + NaCl (aq) + H2O (l)<br />Also used to make vinyl chloride and polyvinyl chloride (PVC)<br />
  6. 6. Hydrochloric acid<br />HCl is 27th on the Top 50 list of chemicals.<br />Most is produced as a by-product of the chlorination of organic compounds.<br />CH4 (g) + 2Cl2 (g) CH2Cl2 (l) + 2HCl (g)<br />Hydrochloric acid is a strong acid.<br />Concentrated HCl is produced by saturation of water - approximately 12M.<br />In the hardware store, you would find it under the name muriatic acid.<br />
  7. 7. Chlorine oxides<br />Two oxides are made industrially, dichlorine monoxide and chlorine dioxide.<br />Both are used for bleaching paper and flour.<br />A radical, ClO, has been studied as a result of the role it plays in destruction of the ozone layer. Using Freon-12 as an example, CCl2F2:<br />
  8. 8. CHLORINE<br />Cl video<br />
  9. 9. Fluorine<br />Made by electrolyzing an ice-cold solution of KF in HF (1886- Henri Moissan)<br />Most chemically reactive of all nonmetals<br />Strong oxidizing agent<br />Forms compounds w/ elements except He, Ne, Ar<br />HF acid is used to etch glass<br />Used to separate the isotopes of Uranium<br />
  10. 10. Iodine and Bromine<br />Br is obtained from sea water and salt-well brines<br />2NaBr(aq) + Cl2(g)------2NaCl(aq) + Br2(l)<br />Iodine used to be extracted from ashes of seaweeds; now it is produced from sodium iodate ( NaIO3)<br />Iodine is necessary for the thyroid gland to work properly<br />