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Halogen

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Periodic table of elements with the Halogens illustrated with black border.

Halogens are extremely reactive chemical elements found in a group on the right side of the periodic table. Their name derives from the greek word for salt (halas) and the verb generate (gennao), because halogens combine with metals to form salts so easily.

History

The name halogen was given to this elemental group because of its element's abilities to form salts when they reacts with metals. An 18th century french scientist created this name for this group and it has not changed since. The elements that fall into this group are Chlorine(Cl), Bromine(Br), Iodine(I), Astatine(At), and one element that was only recently[1] discovered, Ununseptium(Uus). The halogen group is the only group which contains all three kinds of matter; it consists of two solids, two gases, and one liquid.[2] The two solids are Iodine, and Astatine, the liquid is Bromine, and the two gases are chlorine and fluorine.[3]

Chemical Makeup

In their natural form, halogens exist as diatomic compounds. They need only one more electron to fill their valence shells. Because of their tendency to take on only one electron, they typically form a single negatively charged ion. An ion that has this charge, and is formed through the halogens is called a halide. These halides are most abundantly found in salts. [4]

halogen molecule structure model d(X−X) / pm
(gas phase)
d(X−X) / pm
(solid phase)
fluorine
F2
Difluorine-2D-dimensions.png
Fluorine-3D-vdW.png
143
149
chlorine
Cl2
Dichlorine-2D-dimensions.png
Chlorine-3D-vdW.png
199
198
bromine
Br2
Dibromine-2D-dimensions.png
Bromine-3D-vdW.png
228
227
iodine
I2
Diiodine-2D-dimensions.png
Iodine-3D-vdW.png
266
272

Elements

Group 17
Period
2 9
F
3 17
Cl
4 35
Br
5 53
I
6 85
At
7 117
Uus

Fluorine

Fluorine was first discovered in 1886 by a man named Joseph Henri Moissan. Its name comes from the Latin word fluo, which means "flow". It can be found in mineral fluorite, and is used in refrigerants. The symbol for fluorine is "F". it has the atomic number of 9, and has an atomic mas of about 19 amu. The half life for fluorine is about 1.8 hours. The melting point for fluorine is -219.62 degrees celsius, and its boiling point is 188.14 degrees celsius. It has a cubic crystal structure and has a greenish color.[5]

Chlorine

Chlorine was first discovered in 1774 by a man named Carl Wilhelm Scheele. Its name comes from the Greek word Khloros, which means "green". It can be found in salts, and is commonly used in water purification and bleaches. The symbol for chlorine is "Cl". It has an atomic number of 17, and the atomic mass of about 35 amu. The half life for Chlorine ranges from 37 minutes, to 301000 years, and has 2 completely stable isotopes. Its melting point is -100.98 degrees celsius, and its boiling point is -34.6 degrees celsius. It has an orthorhombic crystal structure, and has a greenish color.[6]

Bromine

Bromine was first discovered in 1826 by a man names Antoine J. Balard. Its name comes from the Greek word bromos, which means "stench". It can be found in sea water, and is used in poisons. The symbol for bromine is "Br". Bromine has an atomic number of 35, and an atomic mass of about 80 amu. The half life for Bromine ranges from 3 minutes to 1.5 days, and has 2 completely stable isotopes. Its melting point is -7.2 degrees celsius, and its boiling point is 58.78 degrees celsius. it has a orthorhombic crystal structure and has a reddish color.[7]

Iodine

Iodine was first discovered in 1811 by a man named Bernard Courtois. Its name comes from the Greek word iodes, which means "violet". It can be found in sodium and potassium compounds, and is used in parts of the human body. The symbol for Iodine is "I". It has an atomic number of 53, and has an atomic mass of about 127 amu. The half life of Iodine ranges from 1.7 minutes to 1.6 years, and has one completely stable isotope. Its melting point is 113.5 degrees celsius, and its boiling point is 184 degrees celsius. It produces an orthorhombic crystal structure and has a blackish color. [8]

Astatine

Astatine was first discovered in 1940 by a man named D.R. Corson. Its name comes from the Greek word astatos, which means "unstable". It is a man made element, and there are no uses known for it yet. The symbol for Astatine is "At". It has an atomic number of 85, and an atomic mass of about 210 amu. The half life for it ranges from .1 milliseconds to 7.2 hours. It has no stable isotopes. Its melting point is about 302 degrees celsius, and its boiling point is about 337 degrees celsius. it has an unknown crystal structure and color.[9]

Properties

Halogen Atomic Mass (u) Melting Point (K) Boiling Point (K) Electronegativity (Pauling)
Fluorine 18.998 53.53 85.03 3.98
Chlorine 35.453 171.6 239.11 3.16
Bromine 79.904 265.8 332.0 2.96
Iodine 126.904 386.85 457.4 2.66
Astatine (210) 575 610 ? 2.2
Ununseptium (291)* * * *

* Ununseptium has only recently been discovered; chart values are either unknown if no value appears, or are estimates based on other similar chemicals.


Because of their need for only a single electron, the elements in the halogen group are extremely reactive. Their high reactivity makes it possible for them to be easily harmful, and in some cases even lethal to a biological organism, granted that enough is provided. The most reactive of these elements is Fluorine. It has been known to attack glass, and form compounds with noble gasses. It is one of the most deadly, and corrosive toxic gasses. In another case, Chlorine and Iodine are very effective disinfectants. They have reactive properties that allow them to kill many microorganisms that could be harmful to biological organisms, a process which is known as sterilization. Because of their tendency to take on only one electron, they typically form a single negatively charged ion. An ion that has this charge, and is formed through the halogens is called a halide. when a halide ion reacts with a hydrogen atom, it forms a hydroholic acid. The hydroholic acids are very strong. Examples of a few forms of hydroholic acids would be (HF, HCl, HBr, HI). Even then, these hydroholic acids can react with each other and form interhalogen compounds. These compounds have properties that are very similar to the pure halogens.[10] One of the most interesting features that this group of elements has is its ability to oxidize. Fluorine has an extremely high and strong oxidizing ability, and will cause many other elements to react and have their highest possible oxidation number. Chlorine will react directly with many elements, it bromine, and iodine will react quite readily with many other elements, but many times, UV light or heat is required.[11]

Occurrences

The halogens typically are found very abundantly in many synthetic organic compounds like plastic polymers. These organic compounds are known as halogenated compounds, or are better known as organic halides. Out of all the halogens, Chlorine is by far the most abundant. It is a very important element that is used in the processes that our brain makes mediating the action of the inhibitory transmitter (GABA). Chlorine can also be found in stomach acid as a disinfectant. The body also uses other halogens, such as iodine. Iodine can be found in small amounts being used in producing the thyroid hormones, like thyroxine. Even though these halogens are used in the body as necessities, there are some that are argued not to be as important to the human functions. fluorine and bromine can be found in the body, but are not considered a necessity of the body to work, however, fluoride can be found in some small amounts in and around the mouth. [12]

Uses

Chlorine and Iodine are very effective disinfectants. Because of this, they are used for many different jobs such as cleaning swimming pools, filtering water, washing dishes, and killing the bacteria in fresh wounds and on kitchen surfaces. Many fabric bleaches are known to have Chlorine in them as the active ingredient with which the clothes are cleaned. As well as this, there are many new drugs being discovered and implemented that use halogens as main ingredients. For example, because of the use of halogens in medicine, analogues have been made that are more lipophilic (easily dissolve in fats but not in water), and not as soluble by water. Because of this, halogens can be used to help the penetration through lipid membranes. This dramatically helps medical science.[13]

References

  1. Superheavy element 117 makes debut International team fills gap in the periodic table, by Alexandra Witze, Web edition : Tuesday, April 6th, 2010, accessed 7 April 2010.
  2. [1]
  3. [2]
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  5. [4]
  6. [5]
  7. [6]
  8. [7]
  9. [8]
  10. [9]
  11. [10]
  12. [11]
  13. [12]

Additional Information