Sodium iodide
Sodium iodide
Sodium iodide
Sodium iodide
Sodium iodide

NaI(Tl) scintillators
3D model (JSmol)
ECHA InfoCard 100.028.800 Edit this at Wikidata
RTECS number
  • WB6475000
  • InChI=1S/HI.Na/h1H;/q;+1/p-1 checkY
  • InChI=1/HI.Na/h1H;/q;+1/p-1
  • [Na+].[I-]
Molar mass 149.894[1]
Appearance white solid
Odor odorless
Density 3.67 g cm−3[1]
Melting point 661 °C (1,222 °F; 934 K)[1]
Boiling point 1,304 °C (2,379 °F; 1,577 K)[1]
1587 g/L (0 °C)
1842 g/L (25 °C)
2278 g/L (50 °C)
2940 g/L (70 °C)
3020 g/L (100 °C)[2][3]
Solubility ethanol, acetone[1]
Band gap 5.89 eV[4][5]
−57×10−6 cm3 mol−1[6]
1.93 (300 nm)
1.774 (589 nm)
1.71 (10 μm)[7]
Halite, cF8
Fm3m, No. 225
a = 0.6462 nm
52.1 J mol−1 K−1
98.5 J mol−1 K−1
−287.8 kJ mol−1
−286.1 kJ mol−1
Occupational safety and health (OHS/OSH):
Main hazards
Irritant, can harm the unborn child
GHS labelling:
GHS07: Exclamation markGHS09: Environmental hazard
H315, H319, H400
P273, P305+P351+P338[10]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
Flash point Non-flammable
Safety data sheet (SDS) [1]
Related compounds
Other anions
Sodium fluoride
Sodium chloride
Sodium bromide
Sodium astatide
Other cations
Lithium iodide
Potassium iodide
Rubidium iodide
Caesium iodide
Francium iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions (I) in a crystal lattice. It is used mainly as a nutritional supplement and in organic chemistry. It is produced industrially as the salt formed when acidic iodides react with sodium hydroxide.[11] It is a chaotropic salt.


Food supplement

Sodium iodide, as well as potassium iodide, is commonly used to treat and prevent iodine deficiency. Iodized table salt contains 10 ppm iodide.[11]

Organic synthesis

Monatomic NaI chains grown inside double-wall carbon nanotubes.[12]

Sodium iodide is used for conversion of alkyl chlorides into alkyl iodides. This method, the Finkelstein reaction,[13] relies on the insolubility of sodium chloride in acetone to drive the reaction:[14]

R–Cl + NaI → R–I + NaCl

Nuclear medicine

Some radioactive iodide salts of sodium, including Na125I and Na131I, have radiopharmaceutical uses for thyroid cancer and hyperthyroidism or as radioactive tracer in imaging (see Isotopes of iodine > Radioiodines I-123, I-124, I-125, and I-131 in medicine and biology).

Thallium-doped NaI(Tl) scintillators

Sodium iodide activated with thallium, NaI(Tl), when subjected to ionizing radiation, emits photons (i.e., scintillate) and is used in scintillation detectors, traditionally in nuclear medicine, geophysics, nuclear physics, and environmental measurements. NaI(Tl) is the most widely used scintillation material. The crystals are usually coupled with a photomultiplier tube, in a hermetically sealed assembly, as sodium iodide is hygroscopic. Fine-tuning of some parameters (i.e., radiation hardness, afterglow, transparency) can be achieved by varying the conditions of the crystal growth. Crystals with a higher level of doping are used in X-ray detectors with high spectrometric quality. Sodium iodide can be used both as single crystals and as polycrystals for this purpose. The wavelength of maximum emission is 415 nm.[15]


António Egas Moniz searched for a radiocontrast agent for cerebral angiography.[16] After experiments on rabbits and dogs he settled upon sodium iodide as the best medium.[16]

Solubility data

Sodium iodide exhibits high solubility in some organic solvents, unlike sodium chloride or even bromide:

Solvent Solubility of NaI (g NaI/kg of solvent at 25 °C)[17]
H2O 1842
Liquid ammonia 1620
Liquid sulfur dioxide 150
Methanol 625–830
Formic acid 618
Acetonitrile 249
Acetone 504[18]
Formamide 570–850
Acetamide 323 (41.5 °C)
Dimethylformamide 37–64
Dichloromethane 0.09[19]


Iodides (including sodium iodide) are detectably oxidized by atmospheric oxygen (O2) to molecular iodine (I2). I2 and I complex to form the triiodide complex, which has a yellow color, unlike the white color of sodium iodide. Water accelerates the oxidation process, and iodide can also produce I2 by photooxidation, therefore for maximum stability sodium iodide should be stored under dark, low temperature, low humidity conditions.

See also


  1. ^ a b c d e f Haynes, p. 4.86
  2. ^ Seidell, Atherton (1919). Solubilities of inorganic and organic compounds c. 2. D. Van Nostrand Company. p. 655.
  3. ^ Haynes, p. 5.171
  4. ^ Miyata, Takeo (1969). "Exciton Structure of NaI and NaBr". Journal of the Physical Society of Japan. 27 (1): 266. Bibcode:1969JPSJ...27..266M. doi:10.1143/JPSJ.27.266.
  5. ^ Guizzetti, G.; Nosenzo, L.; Reguzzoni, E. (1977). "Optical properties and electronic structure of alkali halides by thermoreflectivity". Physical Review B. 15 (12): 5921–5926. Bibcode:1977PhRvB..15.5921G. doi:10.1103/PhysRevB.15.5921.
  6. ^ Haynes, p. 4.130
  7. ^ Haynes, p. 10.250
  8. ^ Davey, Wheeler P. (1923). "Precision Measurements of Crystals of the Alkali Halides". Physical Review. 21 (2): 143–161. Bibcode:1923PhRv...21..143D. doi:10.1103/PhysRev.21.143.
  9. ^ Haynes, p. 5.36
  10. ^ "Sodium iodide 383112". Sigma Aldrich.
  11. ^ a b Lyday, Phyllis A. (2005). "Iodine and Iodine Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 382–390. doi:10.1002/14356007.a14_381. ISBN 978-3527306732.
  12. ^ Senga, Ryosuke; Suenaga, Kazu (2015). "Single-atom electron energy loss spectroscopy of light elements". Nature Communications. 6: 7943. Bibcode:2015NatCo...6.7943S. doi:10.1038/ncomms8943. PMC 4532884. PMID 26228378.
  13. ^ Finkelstein, Hank (1910). "Darstellung organischer Jodide aus den entsprechenden Bromiden und Chloriden". Ber. Dtsch. Chem. Ges. (in German). 43 (2): 1528–1532. doi:10.1002/cber.19100430257.
  14. ^ Streitwieser, Andrew (1956). "Solvolytic Displacement Reactions At Saturated Carbon Atoms". Chemical Reviews. 56 (4): 571–752. doi:10.1021/cr50010a001.
  15. ^ "Scintillation Materials and Assemblies" (PDF). Saint-Gobain Crystals. 2016. Archived from the original (PDF) on October 31, 2017. Retrieved June 21, 2017.
  16. ^ a b "Antonio Egas Moniz (1874-1955) Portuguese Neurologist". JAMA: The Journal of the American Medical Association. 206 (2). American Medical Association (AMA): 368–369. 1968. doi:10.1001/jama.1968.03150020084021. ISSN 0098-7484. PMID 4877763.
  17. ^ Burgess, John (1978). Metal Ions in Solution. Ellis Horwood Series in Chemical Sciences. New York: Ellis Horwood. ISBN 9780470262931.
  18. ^ Kowalczyk, James J. (15 April 2001). "Sodium Iodide". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rs087.
  19. ^ De Namor, Angela F. Danil; Traboulssi, Rafic; Salazar, Franz Fernández; De Acosta, Vilma Dianderas; De Vizcardo, Yboni Fernández; Portugal, Jaime Munoz (1989). "Transfer and partition free energies of 1:1 electrolytes in the water–dichloromethane solvent system at 298.15 K". Journal of the Chemical Society, Faraday Transactions 1. 85 (9): 2705–2712. doi:10.1039/F19898502705.

Cited sources