Chemistry:Sodium iodide

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Sodium iodide
Sodium iodide
Sodium iodide
NaI(Tl) scintillators
3D model (JSmol)
RTECS number
  • WB6475000
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
Main hazards Irritant, can harm the unborn child
Safety data sheet [1]
GHS pictograms GHS07: HarmfulGHS09: Environmental hazard
GHS Signal word Danger
H315, H319, H400
P273, P305+351+338[10]
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
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, such as in the treatment of 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]

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)[16]
H2O 1842
Liquid ammonia 1620
Liquid sulfur dioxide 150
Methanol 625–830
Formic acid 618
Acetonitrile 249
Acetone 504
Formamide 570–850
Acetamide 323 (41.5 °C)
Dimethylformamide 37–64
Dichloromethane 0.09[17]


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. 1.0 1.1 1.2 1.3 1.4 1.5 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. doi:10.1143/JPSJ.27.266. Bibcode1969JPSJ...27..266M. 
  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. doi:10.1103/PhysRevB.15.5921. Bibcode1977PhRvB..15.5921G. 
  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. doi:10.1103/PhysRev.21.143. Bibcode1923PhRv...21..143D. 
  9. Haynes, p. 5.36
  10. "Sodium iodide 383112". 
  11. 11.0 11.1 Lyday, Phyllis A. (2005). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 382–390. doi:10.1002/14356007.a14_381. 
  12. Senga, Ryosuke; Suenaga, Kazu (2015). "Single-atom electron energy loss spectroscopy of light elements". Nature Communications 6: 7943. doi:10.1038/ncomms8943. PMID 26228378. Bibcode2015NatCo...6.7943S. 
  13. Finkelstein, Hank (1910). "Darstellung organischer Jodide aus den entsprechenden Bromiden und Chloriden" (in de). Ber. Dtsch. Chem. Ges. 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". Saint-Gobain Crystals. 2016. 
  16. Burgess, John (1978). Metal Ions in Solution. Ellis Horwood Series in Chemical Sciences. New York: Ellis Horwood. ISBN 9780470262931. 
  17. 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

  • Haynes, William M., ed (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 4.49. ISBN 9781498754293. 

External links

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