24.2 part 3
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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)
ChlorineUsesAbout 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
brines2NaBr(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