The Halogens

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Rachel Simm L6WY

The Halogens


        The word ‘halogen’ is from the Greek word meaning for ‘salt producing’. Jӧn Jacob Berzelius in the early nineteenth century used it to indicate that chlorine, bromine and iodine all occur in the sea as salts.

        The halogens all have common characteristics excluding astatine, as it is highly radioactive. These characteristics are: -


Fluorine occurs naturally as fluorspar (fluorite), CaF2, and Cryolite Na3AlF6. These deposits are quite thin and are rarely economical to extract. However Fluorine can occur as semi-precious minerals, which are mine, polished and used for their appearance e.g. Blue John instead of its chemical properties. Fluorine is unable to be oxidized, as there is no existing agent strong enough to oxidize fluorine.  

Chlorine is the most common halogen found in nature, it is commonly found as sodium chloride in seawater and rock salt. It also occurs in all living organisms. Roughly 30g of sodium chloride are found in every kilogram of seawater.

Bromine is a much rarer element. Approximately 70 parts per million of seawater are bromides which can be extracted economically.  

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Iodine is present at 0.05 p.p.m of seawater. However certain varieties of seaweed concentrate iodides greatly. The main source of iodine is sodium iodate (V) NaI03 found only in Chile.

The chlor-akali industry is the production of chlorine by electrolysis of brine (concentrated rock salt in water) and the production of sodium hydroxide. Flowing mercury is cathode used and the sodium produced dissolved into the mercury to form an amalgam. The sodium is then extracted and the mercury is recycled. The use of recycling the mercury means that all the products are useful. Also no energy has to be inputted to ...

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