NaI

Sodium iodide, NaI, is an inorganic salt composed of sodium cations and iodide anions. It forms white, colorless crystals that are highly soluble in water and moderately hygroscopic. In the solid state it adopts the rock-salt lattice and is stable under normal conditions, though iodide can be oxidized to iodine by strong oxidizers.

Preparation and production typically involve direct combination of sodium metal with iodine to form NaI, or the reaction of hydroiodic acid with sodium hydroxide or sodium carbonate. In the laboratory, NaI can also be prepared by metathesis from other iodide salts.

Applications of sodium iodide are varied. In radiation detection, it is used as the primary scintillator when doped with thallium, producing light in the blue region upon gamma-ray interaction; NaI(Tl) crystals are common components of gamma-ray spectrometers and medical imaging devices. In nutrition and medicine, sodium iodide serves as a source of iodide for dietary supplements and iodized salt to prevent iodine deficiency, although potassium iodide is also widely used for this purpose. In organic and analytical chemistry, NaI is employed as an iodide source for synthesis, including Finkelstein reactions that convert alkyl chlorides or bromides to iodides and in various iodometry and iodide-based assays.

Safety considerations are modest but important. Sodium iodide can cause irritation in eyes or skin and is harmful in large doses due to thyroid effects. It is soluble in water, so spills should be cleaned promptly, and it should be stored in a dry place away from oxidizers.