Silver iodide

Silver iodide
Names


Other names Silver(I) iodide
Identifiers
CAS Number	7783-96-2^Y
3D model (Jmol)	Interactive image
ChemSpider	22969^Y
ECHA InfoCard	100.029.125
EC Number	232-038-0
PubChem	6432717
UNII	81M6Z3D1XE^Y
InChI InChI=1S/Ag.HI/h;1H/q+1;/p-1^Y Key: MSFPLIAKTHOCQP-UHFFFAOYSA-M^Y InChI=1/Ag.HI/h;1H/q+1;/p-1 Key: MSFPLIAKTHOCQP-REWHXWOFAV
SMILES [Ag]I
Properties
Chemical formula	AgI
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)
Solubility in water	3×10⁻⁷g/100mL (20 °C)
Solubility product (K_sp)	8.52 × 10 ⁻¹⁷
Solubility	soluble in acid
Structure
Crystal structure	hexagonal (β-phase, < 147 °C) cubic (α-phase, > 147 °C)
Thermochemistry
Std molar entropy (S^o₂₉₈)	115 J·mol⁻¹·K⁻¹^[1]
Std enthalpy of formation (Δ_fH^o₂₉₈)	−62 kJ·mol⁻¹^[1]
Hazards
Safety data sheet	Sigma-Aldrich
EU classification (DSD)	not listed
NFPA 704	0 2 0
Flash point	Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is ^YN ?)
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.

Structure

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 face-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

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

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]

Safety

Extreme exposure can lead to argyria, characterized by localized discoloration of body tissue.^[5]

References

1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X.
↑ 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.
↑ 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.
↑ Phyllis A. Lyday "Iodine and Iodine Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a14_381
↑ "Silver Iodide". TOXNET: Toxicogy Data Network. U.S. National Library of Medicine. Retrieved 9 March 2016.

Wikimedia Commons has media related to Silver iodide.

HI																	He
LiI	BeI₂											BI₃	CI₄	NI₃	I₂O₄, I₂O₅, I₄O₉	IF, IF₃, IF₅, IF₇	Ne
NaI	MgI₂											AlI₃	SiI₄	PI₃, P₂I₄	S	ICl, ICl₃	Ar
KI	CaI₂	Sc	TiI₄	VI₃	CrI₃	MnI₂	FeI₂	CoI₂	NiI₂	CuI	ZnI₂	Ga₂I₆	GeI₂, GeI₄	AsI₃	Se	IBr	Kr
RbI	SrI₂	Y	ZrI₄	Nb	Mo	Tc	Ru	Rh	Pd	AgI	CdI₂	InI₃	SnI₄, SnI₂	SbI₃	TeI₄	I	Xe
CsI	BaI₂		Hf	Ta	W	Re	Os	Ir	Pt	AuI	Hg₂I₂, HgI₂	TlI	PbI₂	BiI₃	Po	AtI	Rn
Fr	Ra		Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Nh	Fl	Mc	Lv	Ts	Og
		↓
		La	Ce	Pr	Nd	Pm	SmI₂	Eu	Gd	TbI₃	Dy	Ho	Er	Tm	Yb	Lu
		Ac	ThI₄	Pa	UI₃, UI₄	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr

Silver compounds

Silver(0,I)	Ag₂F

Silver(I)	AgBF₄ AgBr AgBrO₃ AgCN AgCNO AgCl AgClO AgClO₂ AgClO₃ AgClO₄ AgF AgI AgIO₃ AgMnO₄ AgNO₂ AgNO₃ AgN₃ Ag₃N AgReO₄ AgSCN AgC₂H₃O₂ AgC₂₂H₄₃O₂ AgC₄H₃N₂NSO₂C₆H₄NH₂ AgCF₃SO₃ AgPF₆ Ag₂CO₃ Ag₂C₂ Ag₂C₂O₄ Ag₂CrO₄ Ag₂MoO₄ Ag₂O Ag₂S Ag₂SO₃ Ag₂S₂O₃ Ag₂SO₄ AgHSO₄ Ag₂Se Ag₂SeO₃ Ag₂Te Ag₃AsO₄ Ag₃PO₄ KAg(CN)₂ RbAg₄I₅ Ag(NH₃)₂NO₃

Silver(II)	AgF₂

Silver(III)	Ag₂O₃ AgF₃ Ag₂S₃

Silver(I,III)	Ag₄O₄

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