The element fluorine (F), chlorine (cl),Bromine (Br), Iodine (I) and Astatine (At) are called halogen.
(Greek word hals means salts and gennan means to form or generate).
Thus halogens are literally the salt formers.They are members of VIIA group. Astatine is special halogen and first four mr]embers are standard halogens.
It is radioactive. The most stable isotope Of astatine has a half life of 8.3 hours.
General Properties of Halogens:
- All the halogens exist as discrete diatomic molecule.
- Colour and state: Fluorine and Chlorine are gasses. Fluorine has pale yellow and chlorine has greenish yellow colours. Bromine is a liquid of red brown color. Iodine is a solid of greyish black colour.
- Odour and body effect: All the halogen have irritating odour. They attack the skin. Bromine produces burns that heat slowly.
- The outer shell electronic configuration of halogen is ns2np5. It is an electron of noble gases short of a stable octet.
- Atomic Size: The atomic size of halogen increases from fluorine to iodine.
- Ionization Energy: The ionization of halogens decreases from fluorine to iodine. It means that valences electrons in fluorine are very tightly bound and in iodine valence electrons are loosely bound.
- Electron affinity: The electron affinity values of halogens of halogen are high and negative.
- Electronegativity: The halogen have very high electronegativity. Fluorine is the most electronegativity element. Their Electronegativity decreases from fluorine to iodine.
- Electrode Potential: The halogens have large, positive standard electrode potential.On this basis halogens are use oxidizing.
- Intermolecular forces: The intermolecular forces increase from fluorine to iodine. The reason is that atomic size increases from fluorine to iodine. The large size atoms show more polarizability than small size atoms.
Hence vander waal’s forces in iodine are stronger than other halogens.
Occurence of Halogen:
We should realize that there are typically elements with higher electronegativity values as negative ions. The element with lower values of electronegativity exist as positive ions. The element with intermediate values of electronegativity exist as ions or molecules or in free form.
None of the halogen is found in free form in nature . They are found in the form of compounds.Their most common state is the halide are soluble in water. We are therefore found in salt ponds, sea and surface salt beds.
- Fluorine occurs as Fluorspar ,Caf2, cryolite Na3Alf6, Apatite CaF2.3Ca3(PO4)2.
- Chlorine occurs as Halite, Nacl: NaCl is found are form in brine wells, and Sea water.
- Iodine occurs as NaIO3 (Sodium iodate) and NaIO4 ( Sodium per iodate) in chile brine wells.