The Halogens: Fluorine, Chlorine, Bromine, and Iodine

The four halogens Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I) are very reactive. I left out Astatine (At) because it’s so rare (yes, even more than Francium).

The Halogens

The halogens are a group of chemical elements (group 17 on the periodic table) containing Fluorine, Chlorine, Bromine, and Iodine.

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These elements are known for their chemical reactivity towards other substances. Fluorine and Chlorine are both gases at room temperature, Fluorine is pale yellow and Chlorine is pale green. Bromine, however, is a reddish-brown liquid at room temperature, and Iodine is a black-purple solid.


Fluorine (F) is the first halogen on the Periodic Table of Elements and it has an atomic number of 9. At normal room temperature and air pressure, Fluorine forms a diatomic bond between every two of it’s atoms (F2). Fluorine is extremely reactive to practically all organic and inorganic substances (the most reactive of all substances). For that reason, it’s very difficult to handle as most surfaces oxidize on contact with Fluorine. Commercially, passivated cylinders are used to move and store Fluorine. It is used for etching glass and Tungsten in industry as Tungsten has a very high melting point (the highest of a metal). Although it may not be visible, Fluorine is a very pale yellow-brown colour. In it’s liquid state, Fluorine is less reactive and easier to handle. In it’s solid state at very low temperatures, it loses even more reactivity with elements such as Mercury (Hg).

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Chlorine (Cl) is the second halogen on the Periodic table. It is also very poisoness and the second most reactive halogen next to Fluorine. It is a pale green gas with an atomic number of 17. It also forms a diatomic bond between it’s atoms, as do all the halogens. Chlorine is the most abundant halogen in nature; it is found in great concentrations in seas and oceans in the form of NaCl (table salt in your everyday kitchen). Nowadays, Potassium Iodide (KI) is added to table salt for Iodine supliment.

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Bromine (Br) is the third halogen and the only liquid one. It has an atomic number of 35 and is diatomic (Br2). It is a red-brown coloured liquid which reacts with many substances. One of these reactions is the popular Aluminum in Bromine. After aluminum foil is placed in Bromine liquid, it will form Aluminum Bromide (AlBr3) after a small activity period. Bromine is concentrated in the Dead Sea between Palestine and Jordan along with Chlorine. Chlorine is passed through bromide salts in a single displacement reaction yielding pure Bromine (2NaBr + Cl2 = 2NaCl + Br2).

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Iodine (I) is the fourth halogen and the first solid one. It is also diatomic and has an atomic number of 53. If heated enough, Iodine sublimates (goes from solid to gas right away). The word “Iodine” in Greek means violet hence it’s vapor colour. Iodine is mainly used in first aid for antiseptics with Povidone because of it’s ability to kill germs. One of the coolest reactions for high school is the Iodine – Aluminum reaction (3I2 + 2Al = 2AlI3). This reaction releases a rich purple Iodine vapour which is very beautiful.

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The halogens are very reactive and dangerous but learning about them is loads of fun. Some schools even have Fluorine gas but it’s rare. If you liked my article, please comment and click on that “I Like It” button below. Good luck and don’t do something stupid!

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2 Responses to “The Halogens: Fluorine, Chlorine, Bromine, and Iodine”
  1. mkd1788 Says...

    On December 11, 2009 at 2:03 pm

    informative post..i think one day will be scientist…make research…all the best

  2. cutedrishti8 Says...

    On December 11, 2009 at 2:08 pm

    Nice researched and well presented…

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