Selenium dioxide
 |
|
 |
|
 |
|
| Names | |
|---|---|
| Other names
Selenium(IV) oxide
Selenous anhydride |
|
| Identifiers | |
|
3D model (Jmol)
|
|
| ChemSpider | |
| ECHA InfoCard | 100.028.358 |
|
PubChem CID
|
|
| RTECS number | VS8575000 |
| UNII | |
| UN number | 3283 |
|
|
|
|
| Properties | |
| SeO2 | |
| Molar mass | 110.96 g/mol |
| Appearance | White, yellowish white, or red crystalline solid |
| Odor | rotten radishes |
| Density | 3.954 g/cm3, solid |
| Melting point | 340 °C (644 °F; 613 K) (sealed tube) |
| Boiling point | 350 °C (662 °F; 623 K) subl. |
| 38.4 g/100 mL (20 °C) 39.5 g/100 ml (25 °C) 82.5 g/100 mL (65 °C) |
|
| Solubility | soluble in benzene |
| Solubility in ethanol | 6.7 g/100 mL (15 °C) |
| Solubility in acetone | 4.4 g/100 mL (15 °C) |
| Solubility in acetic acid | 1.11 g/100 mL (14 °C) |
| Solubility in methanol | 10.16 g/100 mL (12 °C) |
| Vapor pressure | 1.65 kPa (70 °C) |
| Acidity (pKa) | 2.62; 8.32 |
| −27.2·10−6 cm3/mol | |
|
Refractive index (nD)
|
> 1.76 |
| Structure | |
| see text | |
| trigonal (Se) | |
| Hazards | |
| Safety data sheet | ICSC 0946 |
|
EU classification (DSD)
|
Toxic (T) Dangerous for the environment (N) |
| R-phrases | R23/25, R33, R50/53 |
| S-phrases | (S1/2), S20/21, S28, S45, S60, S61 |
| NFPA 704 | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
|
LCLo (lowest published)
|
5890 mg/m3 (rabbit, 20 min) 6590 mg/m3 (goat, 10 min) 6590 mg/m3 (sheep, 10 min) |
| Related compounds | |
|
Other anions
|
Selenium disulfide |
|
Other cations
|
Sulfur dioxide Tellurium dioxide |
| Selenium trioxide | |
|
Related compounds
|
Selenous acid |
|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
|
 (what is   ?) |
|
| Infobox references | |
Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium.
Solid SeO2 is a one-dimensional polymer, the chain consisting of alternating selenium and oxygen atoms. Each Se atom is pyramidal and bears a terminal oxide group. The bridging Se-O bond lengths are 179 pm and the terminal Se-O distance is 162 pm. The relative stereochemistry at Se alternates along the polymer chain (syndiotactic). In the gas phase selenium dioxide is present as dimers and other oligomeric species, at higher temperatures it is monomeric. The monomeric form adopts a bent structure very similar to that of sulfur dioxide with a bond length of 161 pm. The dimeric form has been isolated in a low temperature argon matrix and vibrational spectra indicate that it has a centrosymmetric chair form. Dissolution of SeO2 in selenium oxydichloride give the trimer [Se(O)O]3. Monomeric SeO2 is a polar molecule, with the dipole moment of 2.62 D pointed from the midpoint of the two oxygen atoms to the selenium atom.
The solid sublimes readily. At very low concentrations the vapour has a revolting odour, resembling decayed horseradishes. At higher concentrations the vapour has an odour resembling horseradish sauce and can burn the nose and throat on inhalation. Whereas SO2 tends to be molecular and SeO2 is a one-dimensional chain, TeO2 is a cross-linked polymer.
SeO2 is considered an acidic oxide: it dissolves in water to form selenous acid. Often the terms selenous acid and selenium dioxide are used interchangeably. It reacts with base to form selenite salts containing the SeO2−
3 anion. For example, reaction with sodium hydroxide produces sodium selenite:
...
Wikipedia