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    chlorine (Cl)

    chlorine
    A poisonous, greenish-yellow, gaseous element, with a choking smell. Chlorine is one of the halogens. It occurs widely in nature as sodium chloride in seawater and as halite (NaCl), carnalite (KCl.MgCl2.6H2O), and sylvite (KCl). Chlorine is more than twice as dense as air and is quite soluble in water. It does not burn but is a very reactive substance, combining directly with many elements, both metals and non-metals (e.g. sodium and phosphorus) and compounds. In some reactions it acts a strong oxidizing agent by removing hydrogen from compounds. The hydrogen combines with the the chlorine to yield hydrogen chloride. The action of chlorine as a bleaching agent is one example of its oxidizing properties.

    Chlorine was discovered by C. W. Scheele in Uppsala, Sweden, in 1774. Its name comes from the Greek chloros, meaning "pale green".


    Preparation

    Chlorine may be prepared by the oxidation of hydrochloric acid – hydrogen ions are oxidized to water thus releasing the free element chlorine. The usual way of bringing about the reduction is to heat manganese dioxide with concentrated hydrochloric acid. Although the gas is soluble in water, it may be collected over a strong solution of sodium chloride.

    Chlorine is also obtained by the electrolysis of sodium chloride solution using carbon electrodes. Chlorine is liberated at the anode (positive electrode) while sodium is set free at the cathode (negative electrode). However, sodium is so reactive that it reacts with the water – hydrogen is liberated at the same time as sodium hydroxide is formed.


    Atomic number 17
    Atomic mass 35.453
    Electronic configuration 1s22s22p63s23p5
    First ionization energy 1,251 kJ/mol
    Electronegativity 3.2
    Atomic radius 99 pm
    Ionic radius 181 pm
    Density 3.214 g/dm3
    Melting point -101.5 °C (171.6 K)
    Boiling point -34.04 °C (239.1 K)


    Related category

       • INORGANIC CHEMISTRY


    External link
    chlorine (interactive periodic table)



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