Iod

Iod is not a stand-alone element in the periodic table. In most formal contexts the term is either a truncation or misspelling of iodine, or it appears as the root in the chemical prefix “iodo-” used to indicate iodine-containing substituents. Some historical or specialized texts may abbreviate iodination reagents with “iod.,” but as a chemical entry, “iod” by itself has no independent meaning apart from these uses.

Iodine is the element with symbol I and atomic number 53. It is a halogen and relatively rare in Earth’s crust, found mainly in seawater and brines as iodide. Industrial production typically involves extraction from iodide-rich brines or minerals, followed by oxidation to elemental iodine. Iodine exists in several forms and emits violet vapors when heated.

The prefix “iodo-” attaches to organic and inorganic names to signal the presence of an iodine substituent (for example, iodoform, iodide, iodate). The name iodine derives from Greek ioidion, meaning “violet-colored,” a reference to the vapor color.

Iodine is an essential micronutrient required for thyroid hormone synthesis. It is used medically in antiseptics, disinfectants, and as a contrast agent in radiology. Radioisotopes such as I-131 are employed in medical imaging and treatment. Deficiency can cause goiter and developmental issues, while excessive iodine can be toxic. Handling precautions apply to iodine and its compounds due to volatility and irritation.