Halogens


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Halogens

 

the chemical elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At), which form the main subgroup of Group VII of the Mendeleev periodic system. They are called halogens (from the Greek hals, salt) because they form salts (for example, common salt, NaCl) upon combination with metals. The name “halides” is sometimes used. There are seven electrons (configuration s2p5) in the outer electron shell of the halogen atoms, that is, they are one electron short of the stable eight-electron inert-gas configuration (s2p6). Upon reacting with a metal, each halogen atom removes an electron from it, thus showing oxidizing properties. All halogens are very reactive, combining directly with most chemical elements. The chemical reactivity of halogens decreases from fluorine to iodine as the atomic radius increases. Under ordinary conditions fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Astatine is a radioactive element. The molecules of the halogens are diatomic.

References in periodicals archive ?
Geometrical characters of all halogen nitrobenzene complexes (2-4) were found almost similar, and all three halogens (chlorine, bromine and fluorine) interact with nitrobenzene in the same fashion.
Rather than replace halogens with potentially equally harmful substitutes, it would be more logical and effective to address this issue at the e-waste sites.
In task group meetings, it has been stated that the standard is more for show (read: marketing) than substance, and that it does not attempt to provide a scientifically supported reason for why a company would need to limit the halogen content in its products.
A cluster of three bulbs drawing a total of 9 watts of electricity--from a traditional wall outlet--will deliver diffused illumination equivalent to a 40-watt halogen light bulb.
The mystery element commonly combines with halogens. Which of the following elements is not a halogen?
The most commonly reported illnesses and injuries (59%) came from exposure to halogens, and the skin and eyes were the most commonly affected organs.
Tungsten halogen lights are more energy efficient than ordinary incandescents but are also costly to use and present safety issues.
These products consist of halogens, bromine and/or chlorine.
In addition to obvious environmental concerns with halogen gases, the specific degassing process (lance, rotor, etc.) affects the degassing performance more than which gas is used.
The pure white light halogens emit makes them ideal for certain fixtures and situations.
He adds that halogen lamps represent the best opportunity for increasing sales.