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 ?
As a result of these properties it can act as a potential candidate for the halogen bonding and here the main focus of this study was to investigate the halogen bonding ability of different halogens (Cl2, Br2 and F2) and chlorofluorocarbons with nitrobenzene theoretically.
LED lighting can nowbe used to replace existing halogen spotlights and security lights.
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.
Companies have committed to consumers that they will eliminate halogens as part of an environmentally responsible business strategy, regardless of the obvious science.
The first thing to do is to get rid of your halogen torchieres," says Jennifer Thorne, an ACEEE research associate.
Working in Barrow, on the north-central coast of Alaska, Lindberg and his colleagues correlated the buildup of these halogens during the Arctic spring with a dramatic, localized depletion of elemental mercury in the air.
In addition to obvious environmental concerns with halogen gases, the specific degassing process (lance, rotor, etc.
The pure white light halogens emit makes them ideal for certain fixtures and situations.
Halogen-free is defined as both (1) no halogen compounds are intentionally added to the product or used in the manufacturing process for the product, and (2) any impurities present are less than 900 ppm bromine, less than 900 ppm chlorine, and/or less than 1500 ppm total bromine and chlorine.
Elemental halogens have seven valence electrons and are very reactive.
Fyrebloc and Envirostrand products can incorporate other flame retardants such as halogens, in addition to antimony, and can be tailored to suit application requirements.
Joseph Green retired from FMC Corporation where he was a research Fellow working in the area of phosphorus and halogen flame retardants.