Halogen

The halogens [ halogenated ː nə ] (" salt formers ", from Ancient Greek ἅλς halos "salt" and γεννάω gennao " produce " ) form the main group 7 or after re- grouping of the periodic table group 17 in the periodic table of the elements consists of the following six elements: fluorine, chlorine, bromine, iodine, the extremely rare radioactive astatine and the first time in 2010 artificially generated, very unstable Ununseptium. The group of halogens is on the right side of the periodic table between the chalcogens ( 6th main group ) and noble gases ( 8 main group ).

These are non-metals in the elemental state very reactive ( fluorine can react with ignition ), colored and react with metals to form salts ( name origin) and with hydrogen under normal condition to hydrogen halides ( gaseous, monobasic acids).

The former four stable elements play important roles in chemistry, biology and medicine. Astatine is used in organic compounds in nuclear medicine for irradiation of malignant tumors.

• 5.1 halides
• 5.2 hydrogen halides
• 5.3 halogen oxyacids
• 5.4 Inter halogen compounds

Occurrence

Halogens are found in nature mainly as singly negatively charged anions in salts. The corresponding cation is usually an alkali or alkaline earth metal, especially the sodium salts of the halogens are often encountered. From this then the halogens can be obtained by electrolysis. A considerable part of the halides dissolved in seawater.

Important halide compounds:

• Sodium fluoride, NaF
• Aluminiumtrinatriumhexafluorid, Na3 [ AlF6 ] ( cryolite )
• Sodium chloride, NaCl (table salt)
• Potassium chloride, KCl
• Sodium bromide, NaBr
• Potassium bromide, KBr
• Sodium iodide, NaI

In contrast to the other halogens iodine is in the nature as iodate. Astatine, the rarest naturally occurring element, is an intermediate product of the uranium and thorium decay series. The total amount in the earth's crust is only 25 g

Obtaining the pure elements

Fluorine gas F2 can win only through electrochemical processes, since there is no element and compound has a greater redox potential than fluorine and this could oxidize (oxidation, because electron donation of 2 F to F2, other halogens analog).

All other halogens can be produced in addition to the electrochemical representation ( eg chlor-alkali electrolysis) with oxidants such as MnO2 ( pyrolusite ), KMnO4 ( potassium permanganate ).

A further possibility for the production of bromine or iodine is the introduction of chlorine gas as oxidizing agent in concentrated bromide or Iodidlösungen:

Here is for the recovery of chlorine and the above Deacon process ( oxidation-reduction reaction of hydrogen chloride gas with air as the oxidant to form water and chlorine gas ):

Properties

Physical Properties

Elemental halogens are colored, volatile to gaseous substances that are soluble in water ( fluoride reacts ). Your color intensity, boiling points and density increase with the atomic number. They are in the form of diatomic molecules of the form X2 before (eg F2 and Cl2 ) and are therefore non-conductors ( insulators ).

• The color intensity in the gaseous state increases with increasing atomic number.

• Density, melting point and boiling point to take down due to the increase in molecular weight from above. In standard conditions, fluorine and chlorine are gases, bromine is a liquid and iodine resistant.

Chemical Properties

Halogens are highly reactive nonmetals, because they lack only a single valence electron to the full occupation of the valence shell. Since the halogen -halogen bond is not very stable, also halogen molecules react violently; the reactivity decreases as the electronegativity of fluorine to from iodine. Simultaneously, the first ionization energy increases towards the top. However, the properties of astatine are largely unexplored, but it is probably very similar to the iodine from chemical point of view.

• Halogens react with metals to form salts, which earned them their name.

• Halogens react exothermically with hydrogen to form hydrogen halides which, dissolved in water, a more or less strong acids. The violence of the reaction decreases from fluorine to iodine from.

• The solubility in water decreases from the halogens fluorine to iodine, and fluorine with water to form hydrogen fluoride and oxygen react.

• The halogens are increasingly toxic iodine to fluorine.

Use

In organic chemistry, they are used for the synthesis of halogen compounds. The process is generally referred to as halogenation.

By the addition of halogens in incandescent lamps is increased by the tungsten-halogen cycle which lifespan and luminous efficiency. We also speak of halogen lamps.

Compounds

Halides

Ionic halogen compounds such as fluorides, chlorides, bromides and iodides are salt-like substances. Accordingly, they have high melting points, are brittle and electrical non-conductor except in melt and solution. Most halides are soluble in water (such as sodium chloride, sodium chloride, insoluble in water, lead, mercury and silver halides ( cf. hydrochloric acid group ) and copper (I ) halides Many halides occur in nature in the form of minerals before ( s. . below).

Hydrogen halides

• HF, hydrogen fluoride is dissolved in water is a weak acid ( hydrofluoric acid). Due to the strong hydrogen bonds boiling hydrofluoric despite the low molecular weight only at 19.5 ° C.
• HCl, hydrogen chloride dissolves in water to form a strong acid ( hydrochloric acid). Boiling point: -85 ° C
• HBr, hydrogen bromide, in aqueous solution is one of the strongest acids ( hydrobromic acid ). Boiling point: -67 ° C
• HI, hydrogen iodide in water forms the strongest known oxygen-free ( non-complex ) acid ( hydroiodic acid ). Boiling point: -35 ° C

Halogen oxyacids

With the exception of fluorine, the only oxygen acid is unstable Hypofluorous acid halogens are four kinds of oxo acids, which are named as follows:

• HXO: hypohalous acid (Example: hypochlorous acid)
• HXO2: halous acid (Example: chlorous acid)
• HXO3: halogen acid (Example: chloric acid )
• HXO4: perhalogen (example: perchloric acid )

Chlorous acid

Chloric acid

Perchloric

The acid strength increases with increasing number of oxygen atoms, as well as the oxidizing action. Most oxyacids of halogens are very unstable and decompose exothermically.

Inter halogen compounds

Inter- halogen compounds, compounds of the halogens themselves. There are the following types (Y is the more electronegative element ):

• XY: all possible combinations of existing
• XY3: Y is fluorine, chlorine or bromine ( in IBr3 )
• XY5: Y is always fluorine
• XY7: only IF7 known

Inter halogen compounds are unstable at standard conditions or extremely reactive.

There are also Interhalogenidionen such as BrF6 - and - IF6. Also Sauerstoffsäurehalogenide such as perchloryl ClO3F or Iodoxipentafluorid IOF5 are known.