Iodine

Introduction

Iodine is a chemical element with the symbol I and atomic number 53. It is a member of the halogen group that can be found in various states of matter such as solid, liquid, and gas. Iodine and its compounds are primarily used in nutrition, and industrially in the production of acetic acid and certain polymers.

Characteristics

Iodine is a dark-gray/purple-black, lustrous, solid element at standard conditions that sublimes readily to form a violet gas. Its properties are mostly intermediate between those of chlorine and bromine. It is less reactive than the other halogens, which include fluorine, chlorine, and bromine. Iodine exhibits significant nonmetallic character and is a relatively good insulator and a weak conductor of electricity.

History

Iodine was discovered by French chemist Bernard Courtois in 1811. He was extracting sodium and potassium compounds from seaweed ash, and once these were removed, he added sulfuric acid to further process the ash. He observed a violet vapor that crystallized on cold surfaces, which he subsequently identified as a new element.

Occurrence and Production

Iodine is the heaviest essential element utilized widely by life in biological functions. It is primarily obtained from seawater, oil well brines, and nitrate deposits. The world's largest iodine producers are Chile and Japan, where it is obtained from iodate solutions found in natural gas fields and brine water.

Applications

The largest use of iodine is in the production of acetic acid. It is also widely used in medical treatments and industrial processes. Iodine is used as a test for starch and to make solutions for antiseptics. In medicine, radioactive isotopes of iodine can be used to treat thyroid cancer.

Biological Role and Health Effects

Iodine is an essential trace element; the thyroid hormones thyroxine and triiodothyronine contain iodine. In areas where there is little iodine in the diet, typically remote inland areas where no marine foods are eaten, iodine deficiency gives rise to goiter, and in severe cases can lead to cretinism in children, which is a disorder of severely stunted physical and mental growth.

Environmental Impact

Iodine plays a crucial role in the environment as it cycles between the atmosphere, lithosphere, and hydrosphere in various forms. It is both a primary nutrient and a significant pollutant, particularly in the form of iodine-131, a radioactive isotope.