Name: iodine
Symbol: I
Atomic number: 53
Atomic weight: 126.90447 (3)
Group in periodic table: 17
Group name: Halogen
Period in periodic table: 5
Block in periodic table: p-block
CAS registry ID: 7553-56-2
Iodine is a bluish-black, lustrous solid. It volatilises at ambient temperatures into a pretty blue-violet gas with an irritating odour.
It forms compounds with most elements, but is less reactive than the other halogens, which displace it from iodides. Iodine exhibits some metallic-like properties. It dissolves readily in chloroform, carbon tetrachloride, or carbon disulphide to form beautiful purple solutions. It is only slightly soluble in water. Iodine compounds are important in organic chemistry and very useful in medicine and photography. Lack of iodine is the cause of goitre (Derbyshire neck). The deep blue colour with starch solution is characteristic of the free element. It is assimilated by seaweeds from which it may be recovered, and is found in Chilean saltpetre, caliche, old salt brines, and salt wells.