Gourt Home::Gourt :: Silver iodide
| Silver iodide | |
|---|---|
| General | |
| Other names | Silver(I) iodide |
| Molecular formula | AgI |
| Molar mass | 234.773 g/mol |
| Appearance | yellow, crystalline solid |
| CAS number | * |
| Properties | |
| Density and phase | 5.675 g/cm3, solid |
| Solubility in water | 3x10-7g/100mL (20 °C) |
| Melting point | 552°C |
| Boiling point | 1506°C |
| Hazards | |
| EU classification | not listed |
| NFPA 704 | nfpa_f0.pngnfpa_r0.png|
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Chemical infobox | |
Silver iodide (AgI) is a chemical compound used in photography, an antiseptic in medicine, rainmaking and cloud seeding.
The crystalline structure adopted by silver iodide changes with temperature:
- At room temperature (298K), the compound exists as γ-AgI which takes the zinc blende structure.
- Between 409K (136°C) and 419K (146°C), the compound exists as β-AgI which takes the wurtzite structure.
- Above 409K (136°C), the compound exists as α-AgI which has body-centered cubic packed iodide ions with silver ions distributed randomly between 2,3 and 4 coordinate sites.
Silver iodide as a fast ion conductor
The transition between the β and α forms represents the melting of the silver (cation) sublattice. The entropy of fusion (melting) for α-AgI is approximately half that for sodium chloride (a typical ionic solid). This can be rationalised by noting that the AgI crystalline lattice has essentially already partly melted in the transition between α and β forms. Adding the entropy of transition from α-AgI to β-AgI to the entropy of fusion gives a value that is much closer to the entropy of fusion for sodium chloride:
External links
Metal halides | Iodides | Silver compounds | Photographic chemicals | Weather modification | Antiseptics
"Silver iodide"
