Atomic Properties of I
- Atomic Number of I
- 53
- Atomic Mass of I
- 126.9000 u
- Electron Configuration
- [Kr] 4d10 5s2 5p5
- Electronegativity
- 2.66
- Block
- p-block
- Group
- 17
- Period
- 5
Warm iodine crystals and a violet vapor rises above them, making the element appear to vanish into its own signature color. The familiar classroom demonstration is often called sublimation, although under ordinary pressure iodine can also melt before boiling. Either route reveals a dark solid transformed into an unmistakable molecular vapor.
Iodine is the heaviest element that humans need as a nutrient. The thyroid collects iodide ions and uses them to build hormones that regulate metabolism, growth, and development. Too little iodine can enlarge the thyroid and impair health, which is why small amounts of iodide or iodate are added to salt in many countries. A trace element becomes a public-health tool at the dinner table.
Chemistry and medicine make further use of iodine's ability to join organic molecules and absorb radiation. Iodine-containing compounds serve as contrast agents in medical imaging. Povidone-iodine and tincture of iodine remain useful antiseptics. Radioactive iodine-123 can image thyroid function, while iodine-131 can both reveal and treat thyroid tissue because that tissue naturally concentrates iodine.
Natural iodine is almost entirely stable iodine-127. The radioactive isotopes have different clocks and purposes, from hours in diagnostic work to millions of years in environmental tracing.
Iodine is a Collection Agent in two senses: as a halogen it tends to gain an electron, and inside the body the thyroid actively gathers it. The violet vapor is the showpiece; selective collection is the deeper story.