Selenium trioxide

Selenium trioxide
Structural formula of the monomer as found in the gas phase	Space-filling model of the monomer as found in the gas phase
Identifiers
CAS Number	13768-86-0 ;
3D model (JSmol)	monomer: Interactive image; cyclic tetramer: Interactive image;
ChemSpider	103019 ;
ECHA InfoCard	100.033.972
PubChem CID	115128;
CompTox Dashboard (EPA)	DTXSID50895004 ;
	InChI InChI=1S/O3Se/c1-4(2)3 Key: VFLXBUJKRRJAKY-UHFFFAOYSA-N ; InChI=1/O3Se/c1-4(2)3 Key: VFLXBUJKRRJAKY-UHFFFAOYAC;
	SMILES monomer: O=[Se](=O)=O; cyclic tetramer: O=[Se]0(=O)O[Se](=O)(=O)O[Se](=O)(=O)O[Se](=O)(=O)O0;
Properties
Chemical formula	SeO3
Molar mass	126.96 g/mol
Appearance	white hygroscopic crystals
Density	3.44 g/cm3
Melting point	118.35 °C (245.03 °F; 391.50 K)
Boiling point	sublimes
Solubility in water	very soluble
Structure
Crystal structure	tetragonal
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H331, H373, H410
NFPA 704 (fire diamond)	4 0 2 OX
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	7 mg/kg (rat, oral); 7.08 mg/kg (mouse, oral); 5.06 mg/kg (guinea pig, oral); 2.25 mg/kg (rabbit, oral); 13 mg/kg (horse, oral)
LC50 (median concentration)	13 mg/kg (pig, oral); 9.9 mg/kg (cow, oral); 3.3 mg/kg (goat, oral); 3.3 mg/kg (sheep, oral)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Selenium trioxide is the inorganic compound with the formula Se O₃. It is white, hygroscopic solid. It is also an oxidizing agent and a Lewis acid. It is of academic interest as a precursor to Se(VI) compounds.