Halogens





Halogens 3368
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The halogens are the family of chemical elements that includes fluorine (atomic symbol F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The halogens make up Group VIIA of the Periodic Table of the elements. Elemental halogens are diatomic molecules. However, due to their high reactivity, the halogens are never found in nature in native form. The family name means "salt-forming," from the Greek for salt, halos, and for generating genes. The salinity of the oceans on Earth is due in large part to such halogen salts (halides) as sodium chloride (NaCl) and potassium iodide (KI).

Halogens display physical and chemical properties typical of nonmetals. They have relatively low melting and boiling points that increase steadily down the group. Near room temperature, the halogens span all of the physical states: Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. All of the elements are colored, with the color becoming more intense moving down the group. Fluorine gas is pale yellow, and chlorine gas is a yellowish green. Liquid bromine and its vapors are brownish red. Solid iodine appears as shiny, dark gray crystals, and the vapors are a deep purple. The halogens are poor thermal and electrical conductors in all phases, and as solids they are brittle and crumbly. The halogens have distinctive, unpleasant odors, will burn exposed flesh, and are toxic.

The neutral atoms of the halogens possess seven outer electrons. An additional electron can be added to halogen atoms to form singly charged negative ions. These ions have a closed outer-shell configuration. Electronegativity is a measure of the ability of an atom of one element to remove an electron from an atom of another element. As a group, the halogens are among the most electronegative elements. Fluorine has the highest electronegativity of all the elements. Halogens are so reactive that all the elements except helium and neon have been found to react with at least one of the halogens. Fluorine is always assigned a formal oxidation number of –1, whereas the other halogens can exhibit a range of oxidation numbers.

The ability of halogens to form chemical compounds with all metals and most nonmetals has led to a wide variety of uses for these elements. Chlorine is used as a bleach and a disinfectant. Iodine has been used as a topical microbicide. Iodine and bromine are added to halogen lamps to lengthen

Chlorine gas belongs to the halogen chemical family.
Chlorine gas belongs to the halogen chemical family.

the life of the filament and prevent darkening of the bulb. Chloride and iodide are essential dietary minerals for humans. Organic compounds containing halogens are used as fire-retardants (halons), as refrigerants (Freons), and in nonstick coatings (Teflon). Silver bromide and silver iodide have been used in photographic emulsions since the early days of photography. Many halogenated compounds are toxic. A well-known example is DDT (dichlorodiphenyltrichloroethane), once a widely applied pesticide that was banned in the United States after severe environmental effects were discovered. All known isotopes of astatine are radioactive, with the longest-lived isotope having a half-life of about eight hours. Relatively little is known of the physical and chemical properties of astatine. However, it is predicted to have properties similar to iodine.

SEE ALSO Bromine ; Chlorine ; Fluorine ; Iodine .

John Michael Nicovich

Bibliography

Lide, David R., ed. (2003). The CRC Handbook of Chemistry and Physics , 84th edition. Boca Raton, FL: CRC Press.

Internet Resources

Winter, Mark. "WebElements™ Periodic Table." The University of Sheffield and WebElements, Ltd., U.K.. Available from http://www.webelements.com .



Also read article about Halogens from Wikipedia

User Contributions:

Fazalullah
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Oct 12, 2008 @ 2:14 pm
I solved my probilm. Thank you very much, it is very helpful.
Karla
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Feb 9, 2009 @ 8:20 pm
The information is really good and it really helps! thanks!
sylvia
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Aug 25, 2009 @ 6:18 pm
I was so confused about different families of elements. Especially halogens. Thank you for all of your help. Keep doing what you're doing!
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Mar 25, 2010 @ 10:10 am
this article is really helpful, but i would like to know why is it this halogen group has very high electronegativity ?
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Apr 27, 2010 @ 1:13 pm
Why can fluoride prevent iodine in synthesizing two hormones (triiodothyronine and
thryoxine) critical for normal metabolic activity throughout the body?
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May 19, 2010 @ 1:13 pm
how many electrons do halogen atoms have on their outer shell
Jay
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Oct 14, 2010 @ 4:04 am
Thanks for this copied and pasted it all for my assignment in science A* thanks,
upset
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Nov 12, 2010 @ 1:13 pm
I wanted to use your website for a science project, but it has next to nothing about astatine, the element that I'm doing my project on. So, thanks for nothing!
MIDNIGHT
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Nov 30, 2010 @ 6:18 pm
How many electrons does an atom of the Halogen family usually lose?
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Oct 16, 2011 @ 10:22 pm
thank you all, this really helped me in my essay(:
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Oct 31, 2011 @ 12:12 pm
@ elman there are seven electrons in the outer most shell of halogens as there group valency also shows that it contains 7 electrons in their outer most shell.
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Nov 11, 2011 @ 10:10 am
wow this sucks it didnt help me at all this is horible wow get a life
abdulsalam
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May 2, 2012 @ 2:14 pm
what will be the product of the reaction of chlorine and bromine
raghuram
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Sep 10, 2013 @ 9:21 pm
It is good. it helps lot for every one . thank you all, this really helped me in my essay

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