Selenium trioxide is a chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 used in the manufacture of photoelectric cells and solar energy devices.
A laboratory preparation is to react anhydrous K₂SeO₄ and SO₃. The compound is thermodynamically unstable with respect to selenium dioxide

Selenium dioxide

Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium.-Properties:...

. The solid consists of cyclic tetramers, Se₄O₁₂. In the gas phase there is some dissociation into the monomer.
It is a strong oxidizing agent, as is selenic acid

Selenic acid

Selenic acid is the chemical compound with the formula . It is an oxoacid of selenium, and its structure is more accurately described as .As predicted by VSEPR theory, the selenium center is tetrahedral, with a Se–O bond length of 161 pm...

 and all selenate

Selenate

The selenate ion is SeO42–.Selenates are analogous to sulfates and have similar chemistry. They are highly soluble in aqueous solutions at ambient temperatures....

s.

Structure

The molecular shape of selenium trioxide is triagonal planar. Selenium trioxide is a nonpolar molecule. the bonds between the selenium and the oxygen are double bonds. The bond angles are all 120°, and the molecule is flat. There are no lone bonding pairs.