Introduction, History, Properties, and Applications Halogens


Halogens: The chemical elements of Group 17 are called halogens. The word halogen means salt-forming. When halogens react with metals, salts are produced. Halogens include Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At), and Tennessine (Ts). Astatine is a radioactive element with short-lived. Tennessine is a man-made element. Halogen is the only group of the periodic table that has three main states of matter. Halogens react with hydrogen to form acid. These elements have seven electrons in their valence shell. They require one electron to complete their valence shell. Therefore, they are very reactive. Due to their reactivity, they do not occur in free form. They can exist in combined form.



In 1811, German chemist Johann Schweigger put forward that the word halogen means salt-forming. In 1826, Swedish chemist Jacob Berzelius suggested the term halogens for these elements.


Fluorspar (fluorine mineral) was known as early as 1529. Chemists know that fluorspar contains an undiscovered element. But they were unable to isolate it. In 1860, An English chemist George Gore passed electricity through HF and produced F. But he could not prove his result. In 1886, a Peris chemist Henri Moissan electrolyzed the solution of potassium bifluoride with hydrogen fluoride and successfully isolated fluorine. 

Early chemists and alchemists were well-known HCl. However, elemental chlorine was not prepared until 1774. In 1774, Carl Wilhelm Scheele heated HCl with MnO2 and got a new element. He called the new element dephlogisticated muriatic acid. This name was used for 33 years. In 1807, Humphry Davy investigated chlorine and discovered it an actual element.

In 1820, Antoine Jerome Ballard discovered bromine. He discovered it by passing chlorine gas through a sample of brine. He proposed the name muride for the new element. French Academy suggested the name bromine for the new element.

Bernard Courtois used seaweed for the manufacture of saltpeter. He heated the seaweed ash with water to prepare KCl. He added sulfuric acid to this process. He found that his process gave purple fumes. These fumes were condensed into black crystals. He sent samples to other chemists for further investigation. Joseph Gay-Lussac proved iodine to be a new element.

In 1931, Fred Allison asserted that he had been discovered an element with an atomic number 85 by using a magneto-optical machine. He named the element Alabamine but he was wrong. In 1937, Rajendralal De asserted that he had been discovered an element 85. He named the element dakine but he was wrong. In 1939, Horia Hulubei and Yvette Cauhois were unsuccessful in discovering element 85. In the same year, Walter Minder discovered an iodine-like element from the beta decay of polonium. Now, element 85 is named astatine. In 1940, Dale R. Corson, K.R.Mackenzie, and Emilio G. Segre successfully prepared astatine by bombarding BI with AL-FA particles.

In 2010, a team headed by Yuri Oganessiansucces successfully discovered  Tennessie-294 by bombarding berkelium-249 with calcium-48. 

General Properties

The atomic radius of halogens increases down the group. The melting and boiling points of Halogens increase down the group due to van der Waals forces. The atomic size increases down the group. The increase in size increases the strength of van der Waal forces. Ionization energy, electron affinity, and electronegativity of halogens decrease down the group. Halogens are poor conductors of heat and electricity. They are extremely toxic. Their molecules are diatomic. They are highly reactive. They form negative ions.

Colors & States

  • Fluorine is a pale yellow
  • Chlorine is a greenish gas
  • Bromine is a dark red liquid
  • Iodine is a black solid and when heated it forms purple fumes
  • Astatine is a black solid


Fluorine has one stable isotope(fluorine-19) that is naturally occurring. 18 isotopes of F have been discovered with atomic masses ranging from 14 to 31. Chlorine has two stable isotopes (chlorine-35 & chlorine-36) that are naturally occurring. 24 isotopes of Cl have been discovered with atomic masses ranging from 28 to 51. Bromine has two stable isotopes (bromine-79 & bromine-81) that are naturally occurring. 33 isotopes of Br have been discovered with atomic masses ranging from 66 to 98.

Iodine has one stable isotope (iodine-127) that is naturally occurring. 38 isotopes of I have been discovered with atomic masses ranging from 108 to 145. Astatine has no stable isotopes. However, there are 4 naturally occurring radioactive of At. These are astatine-215, astatine-217, astatine-218, and astatine-219. 


Cl and F are used as disinfectants for drinking water, swimming pools, spas, dishes, and surfaces. They kill bacteria through sterilization. Sodium hypochlorite(produced from Cl) is used in the production of paper. Cl reacts with Na to form NaCl. NaCl is used as table salt. Halogens lamps are used nowadays. These lamps are a type of incandescent lamps. These lamps glow at high temperatures with white light.



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