Silver iodide

Last updated
Silver iodide
AgI sample.jpg
Other names
Silver(I) iodide
3D model (JSmol)
ECHA InfoCard 100.029.125
EC Number 232-038-0
PubChem CID
Molar mass 234.77 g/mol
Appearanceyellow, 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)
3×107g/100mL (20 °C)
8.52 × 10 −17
80.0·10−6 cm3/mol
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., waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeSilver iodide
Flash point Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)
Infobox references

Silver iodide is an inorganic compound with the formula Ag I. 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.

An inorganic compound is typically a chemical compound that lacks C-H bonds, that is, a compound that is not an organic compound, but the distinction is not defined or even of particular interest.

Silver Chemical element with atomic number 47

Silver is a chemical element with symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. The metal is found in the Earth's crust in the pure, free elemental form, as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining.

An iodide ion is the ion I. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts, not organoiodine compounds. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of intellectual disability.



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

Iodargyrite halide mineral

Iodyrite or iodargyrite is a natural mineral form of silver iodide.

In materials science, fast ion conductors are solids with highly mobile ions. These materials are important in the area of solid-state ionics, and are also known as solid electrolytes and superionic conductors. These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. As solid electrolytes they allow the movement of ions without the need for a liquid or soft membrane separating the electrodes. The phenomenon relies on the hopping of ions through an otherwise rigid crystal structure.

The entropy of fusion is the increase in entropy when melting a substance. This is almost always positive since the degree of disorder increases in the transition from an organized crystalline solid to the disorganized structure of a liquid; the only known exception is helium. It is denoted as and normally expressed in J mol−1 K−1

The golden-yellow crystals on this mineral sample are iodargyrite, a naturally occurring form of b-AgI. Iodargyrite-263859.jpg
The golden-yellow crystals on this mineral sample are iodargyrite, a naturally occurring form of β-AgI.

Preparation and properties

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. [4] 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.

Potassium iodide chemical compound

Potassium iodide is a chemical compound, medication, and dietary supplement. As a medication it is used to treat hyperthyroidism, in radiation emergencies, and to protect the thyroid gland when certain types of radiopharmaceuticals are used. In the developing world it is also used to treat skin sporotrichosis and phycomycosis. As a supplement it is used in those who have low intake of iodine in the diet. It is given by mouth.

Silver nitrate chemical compound

Silver nitrate is an inorganic compound with chemical formula AgNO
. This compound is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides. It was once called lunar caustic because silver was called luna by the ancient alchemists, who believed that silver was associated with the moon.

Hydroiodic acid is a highly acidic aqueous solution of hydrogen iodide (HI) (concentrated solution usually 48 - 57% HI). It is the second strongest hydrohalic acid, after hydroastatic acid. Hydroiodic acid is a commonly used chemical reagent and is one of the strong acids that ionize completely in an aqueous solution. Concentrated hydroiodic acid has a pH of less than 0.

Cloud seeding

Cessna 210 equipped with a silver iodide generator for cloud seeding Cessna 210 Hagelflieger Detail.jpg
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. [5]

Freezing is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. In contrast, solidification is a similar process where a liquid turns into a solid, not by lowering its temperature, but by increasing the pressure that it is under. Despite this technical distinction, the two processes are very similar and the two terms are often used interchangeably.


Nucleation is the first step in the formation of either a new thermodynamic phase or a new structure via self-assembly or self-organization. Nucleation is typically defined to be the process that determines how long an observer has to wait before the new phase or self-organized structure appears. For example, if a volume of water is cooled below 0° C, it will tend to freeze into ice. Volumes of water cooled only a few degrees below 0° C often stay completely free of ice for long periods. At these conditions, nucleation of ice is either slow or does not occur at all. However, at lower temperatures ice crystals appear after little or no delay. At these conditions ice nucleation is fast. Nucleation is commonly how first-order phase transitions start, and then it is the start of the process of forming a new thermodynamic phase. By contrast, new phases at continuous phase transitions start to form immediately.

Cloud seeding form of weather modification

Cloud seeding is a type of weather modification that aims to change the amount or type of precipitation that falls from clouds by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud. The usual intent is to increase precipitation, but hail and fog suppression are also widely practised in airports where harsh weather conditions are experienced.


Extreme exposure can lead to argyria, characterized by localized discoloration of body tissue. [6]

Argyria medical condition

Argyria or argyrosis is a condition caused by excessive exposure to chemical compounds of the element silver, or to silver dust. The most dramatic symptom of argyria is that the skin turns purple or purple-grey. It may take the form of generalized argyria or local argyria. Generalized argyria affects large areas over much of the visible surface of the body. Local argyria shows in limited regions of the body, such as patches of skin, parts of the mucous membrane or the conjunctiva.

Related Research Articles

Solubility equilibrium is a type of dynamic equilibrium that exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound. The solid may dissolve unchanged, with dissociation or with chemical reaction with another constituent of the solvent, such as acid or alkali. Each type of equilibrium is characterized by a temperature-dependent equilibrium constant. Solubility equilibria are important in pharmaceutical, environmental and many other scenarios.

A halide is a binary phase, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, astatide, or theoretically tennesside compound. The alkali metals combine directly with halogens under appropriate conditions forming halides of the general formula, MX. Many salts are halides; the hal- syllable in halide and halite reflects this correlation. All Group 1 metals form halides that are white solids at room temperature.

Precipitation (chemistry) chemical term

Precipitation is the creation of a solid from a solution. When the reaction occurs in a liquid solution, the solid formed is called the 'precipitate'. The chemical that causes the solid to form is called the 'precipitant'. Without sufficient force of gravity (settling) to bring the solid particles together, the precipitate remains in suspension. After sedimentation, especially when using a centrifuge to press it into a compact mass, the precipitate may be referred to as a 'pellet'. Precipitation can be used as a medium. The precipitate-free liquid remaining above the solid is called the 'supernate' or 'supernatant'. Powders derived from precipitation have also historically been known as 'flowers'. When the solid appears in the form of cellulose fibers which have been through chemical processing, the process is often referred to as regeneration.

A silver halide is one of the chemical compounds that can form between the element silver and one of the halogens. In particular, bromine, chlorine, iodine and fluorine may each combine with silver to produce silver bromide (AgBr), silver chloride (AgCl), silver iodide (AgI), and three forms of silver fluoride, respectively.

Silver chloride chemical compound

Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water (this behavior being reminiscent of the chlorides of Tl+ and Pb2+). Upon illumination or heating, silver chloride converts to silver (and chlorine), which is signaled by grey to black or purplish coloration to some samples. AgCl occurs naturally as a mineral chlorargyrite.

Triiodide anion

In chemistry, triiodide usually refers to the triiodide ion, I
. This anion, one of the polyhalogen ions, is composed of three iodine atoms. It is formed by combining aqueous solutions of iodide salts and iodine. Some salts of the anion have been isolated, including thallium(I) triiodide (Tl+[I3]) and ammonium triiodide ([NH4]+[I3]). Triiodide is observed to be a red colour in solution .

Copper(I) iodide chemical compound

Copper(I) iodide is the inorganic compound with the formula CuI. It is also known as cuprous iodide. It is useful in a variety of applications ranging from organic synthesis to cloud seeding.

Silver oxide chemical compound

Silver(I) oxide is the chemical compound with the formula Ag2O. It is a fine black or dark brown powder that is used to prepare other silver compounds.

Potassium chromate chemical compound

Potassium chromate is the inorganic compound with the formula (K2CrO4). This yellow solid is the potassium salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially. It is a class two carcinogen as it contains hexavalent chromium.

Ionic conduction is the movement of an ion from one site to another through defects in the crystal lattice of a solid or aqueous solution.

An advanced superionic conductor (AdSIC) is fast ion conductor that has a crystal structure close to optimal for fast ion transport (FIT).

Rubidium silver iodide is a ternary inorganic compound with the formula RbAg4I5. Its conductivity involves the movement of silver ions within the crystal lattice. It was discovered while searching for chemicals which had the ionic conductivity properties of alpha-phase silver iodide at temperatures below 146 °C for AgI.

Cobalt(II) iodide chemical compound

Cobalt(II) iodide or cobaltous iodide are the inorganic compounds with the formula CoI2 and the hexahydrate CoI2(H2O)6. These salts are the principal iodides of cobalt.

Solid state ionics

Solid-state ionics is the study of ionic-electronic mixed conductor and fully ionic conductors and their uses. Some materials that fall into this category include inorganic crystalline and polycrystalline solids, ceramics, glasses, polymers, and composites. Solid-state ionic devices, such as solid oxide fuel cells, can be much more reliable and long-lasting, especially under harsh conditions, than comparable devices with fluid electrolytes.

Cobalt(II) hydroxide chemical compound

Cobalt(II) hydroxide or cobaltous hydroxide is the inorganic compound with the formula Co(OH)
, consisting of divalent cobalt cations Co2+
and hydroxide anions HO
. The pure compound, often called the "beta form" is a pink solid insoluble in water.

Tellurium iodide is an inorganic compound with the formula TeI. Two forms are known. Their structures differ from the other monohalides of tellurium. There are three subiodides of tellurium, α-TeI, β-TeI, and Te2I, and one tellurium tetraiodide.

Silver nitrite chemical compound

Silver nitrite is an inorganic compound with the formula AgNO2.


  1. 1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN   978-0-618-94690-7.
  2. Binner, J. G. P.; Dimitrakis, G.; Price, D. M.; Reading, M.; Vaidhyanathan, B. (2006). "Hysteresis in the β–α Phase Transition in Silver Iodine" (PDF). Journal of Thermal Analysis and Calorimetry. 84 (2): 409–412. CiteSeerX . doi:10.1007/s10973-005-7154-1.
  3. Hull, Stephen (2007). "Superionics: crystal structures and conduction processes". Rep. Prog. Phys. 67 (7): 1233–1314. doi:10.1088/0034-4885/67/7/R05.
  4. 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.
  5. Phyllis A. Lyday "Iodine and Iodine Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi : 10.1002/14356007.a14_381
  6. "Silver Iodide". TOXNET: Toxicogy Data Network. U.S. National Library of Medicine. Retrieved 9 March 2016.
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 YI3 ZrI4 NbI5 MoTcRuRhPd AgI CdI2 InI3 SnI4,
SbI3 TeI4 IXe
CsI BaI2   HfI4 TaI5 WReOsIrPt AuI Hg2I2,
TlI PbI2 BiI3 Po AtI Rn
FrRa RfDbSgBhHsMtDsRgCnNhFlMcLvTsOg
LaCePrNdPm SmI2 EuGd TbI3 DyHoErTmYbLu
Ac ThI4 Pa UI3,