Group 15 elements halogens

In order to prepare hydrolytically stable polythionyiphosphazenes the perchlo-rinated polymers were reacted with nucleophiles to substitute the hydrolytically sensitive main group-element halogen bonds [2]. This type of post-polymerization structural modification is well-established in polyphosphazene chemistry [2,8]. Thus, aryloxide nucleophiles or primary amines were used to substitute the polymers leading to poly(aryloxythionylphosphazenes) 24 and poly(amino-thionylphosphazenes) 25 respectively [35,37] ... 

Halogenation. Normally, 2-halopropane derivatives are prepared from isopropyl alcohol most economically by reaction with the corresponding acid haUde. However, under appropriate conditions, other reagents, eg, phosphoms haUdes and elemental halogen, also react by replacement of the hydroxyl group to give the haUde (46). 

Boranes also form derivatives ia which main group elements occupy a bridging position between two boron atoms, rather than a polyhedral vertex. An extensively studied system is -R MB Hg, where R = H, CH, C2H3, halogen, and M = Si, Ge, Sn, Pb (185). The stmcture of l-Br- J.-[(CH3)3Si]-B3H2... 

Derivatives of the boranes include not only simple substituted compounds in which H has been replaced by halogen, OH, alkyl or aryl groups, etc., but also the much more diverse and numerous class of compounds in which one or more B atom in the cluster is replaced by another main-group element such as C, P or S, or by a wide range of metal atoms or coordinated metal groups. These will be considered in later sections. 

Note Such halogenation can be done by addition of elemental halogen to alkenyl or alkynyl groups or by replacement of one or more of the hydrogen atoms attached to alkyl or aryl substituents, using a variety of reagents. 

The only liquid nonmetal does full justice to its name and to its group (the halogens) it stinks and is aggressive. Bromine compounds capture radicals hence the application as flame retardant. Is a component of the previously widespread sleeping agent "Bromural" as a consequence the element became popular (bromine calms). Its most important role is as a silver salt in photography. It is present in small amounts in our bodies (ca. 250 mg), but its function has still not been established. 

Boudreau AE, Mathez EA McCallum IS (1986) Halogen geochemistry of the Stillwater and Bushveld complexes evidence for transport of the platinum-group elements by Cl-rich fluids. J Pet 27 967-986 Boudreau AE, Stewart MA, Spivack AJ (1997) Stable Cl isotopes and origin of high-Cl magmas of the Stillwater Complex, Montana. Geology 25 791-794... 

Symbol Br atomic number 35 atomic weight 79.904 a halogen group element electron affinity 3.36359 eV electronegativity 2.8 electron configuration [Ar] 3di°4s24p5 most stable valence states -1 and -i-5, less stable valence states -1-1 and -i-3 a diatomic molecule (Br2) in liquid and vapor states over a wide range of temperature two stable isotopes, Br-79 (50.57%) and Br-81 (49.43%). 

Favorable elements for the element/halogen exchange at alkyl groups are according to our investigations localized in the marked small area of Scheme 14. 

Halogens (7A group elements) have an oxidation state of -1 in their compounds formed with hydrogen and metals. 

FLUORINE. CAS 7782-41-4], Chemical element symbol F. at. no. 9. at. wt. 18.9984, periodic table group 17 (halogens), mp -2l9,62nC, bp - 188.1°C. density 1.696 g/l (gas at 0CC, 1.108 g/cm (liquid at bp). Fluorine is a pale yellow gas, poisonous, very reaclive. combines with most other elements in the dark, except it does not combine readily with oxygen. Critical pressure is 55 atm critical temperature is -129.2 C. First identified by Scheele in 1771. but not isolated until 1886 by Moissan who electrolyzed fused potassium hydrogen fluoride in a platinum apparatus. Fluorine is a high-tonnage chemical, used mainly in the production of fluorides, in the synthesis of fluorocarbons, and us rut oxidizer for rocket fuel. 

Just as atoms shrink when converted to cations by loss of an electron, they expand when converted to anions by gain of an electron. As shown in Figure 6.2 for the group 7A elements (halogens), the expansion is dramatic. Chlorine, for example, nearly doubles in size, from 99 pm for the neutral atom to 184 pm for the chloride anion. 

Reaction with Halogens The alkali metals react rapidly with the group 7 A elements (halogens) to yield colorless, crystalline ionic salts called halides ... 

Group 7A elements (halogens), such as fluorine, have seven valence electrons and form one bond, as in hydrogen fluoride, HF. The fluorine atom in the resultant molecule has one bonding pair of electrons and three lone pairs. 

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