Silver iodide

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Silver iodide
Jodid stříbrný.PNG
Silver iodide
Other names
Silver(I) iodide
7783-96-2 YesY
ChemSpider 22969 YesY
EC Number 232-038-0
Jmol interactive 3D Image
PubChem 6432717
Molar mass 234.77 g/mol
Appearance yellow, crystalline solid
Odor odorless
Density 5.675 g/cm3, solid
Melting point 558 °C (1,036 °F; 831 K)
Boiling point 1,506 °C (2,743 °F; 1,779 K)
3×10−7g/100mL (20 °C)
8.52 × 10 −17
Solubility soluble in acid
hexagonal (β-phase, < 147 °C)
cubic (α-phase, > 147 °C)
115 J·mol−1·K−1[1]
−62 kJ·mol−1[1]
Safety data sheet Sigma-Aldrich
not listed
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

Silver iodide is an inorganic compound with the formula AgI. The compound is a bright yellow solid, but samples almost always contain impurities of metallic silver that give a gray coloration. The silver contamination arises because AgI is highly photosensitive. This property is exploited in silver-based photography. Silver iodide is also used as an antiseptic and in cloud seeding.


The structure adopted by silver iodide is temperature dependent:[2]

  • Below 420 K, the β-phase of AgI, with the wurtzite structure, is most stable. This phase is encountered in nature as the mineral iodargyrite.
  • Above 420 K, the α-phase becomes more stable. This motif is a body-centered cubic structure which has the silver centers distributed randomly between 2-, 3-, and 4-coordinate sites. At this temperature, Ag+ ions can move rapidly through the solid, allowing fast ion conduction. The transition between the β and α forms represents the melting of the silver (cation) sublattice. The entropy of fusion for α-AgI is approximately half that for sodium chloride (a typical ionic solid). This can be rationalized by considering the AgI crystalline lattice to have already "partly melted" in the transition between α and β polymorphs.
  • A metastable γ-phase also exists below 420 K with the zinc blende structure.
The golden-yellow crystals on this mineral sample are iodargyrite, a naturally occurring form of β-AgI.

Preparation and properties[edit]

Silver iodide is prepared by reaction of an iodide solution (e.g., potassium iodide) with a solution of silver ions (e.g., silver nitrate). A yellowish solid quickly precipitates. The solid is a mixture of the two principal phases. Dissolution of the AgI in hydroiodic acid, followed by dilution with water precipitates β-AgI. Alternatively, dissolution of AgI in a solution of concentrated silver nitrate followed by dilution affords α-AgI.[3] If the preparation is not conducted in the absence of sunlight, the solid darkens rapidly, the light causing the reduction of ionic silver to metallic. The photosensitivity varies with sample purity.

Cloud seeding[edit]

Cessna 210 equipped with a silver iodide generator for cloud seeding

The crystalline structure of β-AgI is similar to that of ice, allowing it to induce freezing by the process known as heterogeneous nucleation. Approximately 50,000 kg are used for cloud seeding annually, each seeding experiment consuming 10–50 grams.[4]


Extreme exposure can lead to argyria characterized by localized discoloration of body tissue.


  1. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X. 
  2. ^ Binner, J. G. P.; Dimitrakis, G.; Price, D. M.; Reading, M.; Vaidhyanathan, B. (2006). "Hysteresis in the β–α Phase Transition in Silver Iodide" (PDF). Journal of Thermal Analysis and Calorimetry 84 (2): 409–412. doi:10.1007/s10973-005-7154-1. 
  3. ^ O. Glemser, H. Saur "Silver Iodide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1036-7.
  4. ^ Phyllis A. Lyday "Iodine and Iodine Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a14_381
LiI BeI2 BI3 CI4 NI3 I2O4,
NaI MgI2 AlI3 SiI4 PI3,
S ICl,
KI CaI2 Sc TiI4 VI3 CrI3 MnI2 FeI2 CoI2 NiI2 CuI ZnI2 Ga2I6 GeI2,
AsI3 Se IBr Kr
RbI SrI2 Y ZrI4 Nb Mo Tc Ru Rh Pd AgI CdI2 InI3 SnI4,
SbI3 TeI4 I Xe
CsI BaI2   Hf Ta W Re Os Ir Pt AuI Hg2I2,
TlI PbI2 BiI3 Po AtI Rn
Fr Ra   Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo
La Ce Pr Nd Pm SmI2 Eu Gd TbI3 Dy Ho Er Tm Yb Lu
Ac ThI4 Pa UI3,
Np Pu Am Cm Bk Cf Es Fm Md No Lr