Halogens: Difference between revisions

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The '''halogens''' are the [[nonmetals|nonmetallic]] [[element|elements]] found in [[chemical group|Group 17]] of the [[periodic table|periodic table of the elements]]: [[fluorine]] ('''F'''), [[chlorine]] ('''Cl'''), [[bromine]] ('''Br'''), [[iodine]] ('''I'''), and [[astatine]] ('''At'''). The name "halogen" (Greek ''halos'', salt and ''-genes'', forming) is derived from their tendency to form a [[salt]] when reacted with a [[metal]].


==Chemistry==
The valence shells of halogen atoms need only one more [[electron]] to form a completely filled shell of either eight or eighteen electrons. As such, the halogens have a strong tendency to form ions with a charge of -1 in order to complete their valence shells. They also do not exist as isolated atoms in their elemental forms; instead, they each share one electron with one other atom to form diatomic molecules.
A third consequence of the halogens' nearly filled valence shell is high [[reactivity]] towards cationic or low-ionization-potential species. Halogen [[anion|anions]] in the body can bind to [[potassium]], [[calcium]] and [[magnesium]] [[cation|cations]], rendering them useless. This is particularly true for fluoride ions, which can easily diffuse through the [[skin]] and enter the bloodstream.
[[hydrohalic acid|Hydrohalic acids]], diatomic compounds of one hydrogen atom and one halogen atom, are particularly strong owing to high halogen [[electron affinity]]. Care should be taken when handling these acids, particularly at high concentrations.
The halogens are found in some [[hypervalent]] compounds (eg. SF<sub>6</sub>) and were instrumental in the formation of the first compounds of the [[noble gas|noble gases]] (eg. XEF<sub>4</sub>). They can also react with each other to form the so-called [[interhalogen|interhalogens]].

Revision as of 23:41, 7 February 2007

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