24.2 part 3
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24.2 part 3 24.2 part 3 Presentation Transcript

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