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The Selenium trioxide Lewis structure is Se–O double bond, Se–O double bond and Se–O double bond; the central Se has 3 electron domains (0 lone pairs), giving a trigonal planar electron-domain arrangement and a trigonal planar molecular geometry with a 120° bond angle. Se is best described as sp2-hybridized, and Selenium trioxide is nonpolar because the bond dipoles cancel by molecular symmetry.
Figure 1: Lewis Structure of Selenium trioxide (O3Se)
| Chemical Formula | O3Se |
| CAS Number | 13768-86-0 |
| Total Valence Electrons | 24 |
| Lewis Structure | Se–O double bond, Se–O double bond and Se–O double bond |
| Electron-Domain Geometry | trigonal planar |
| Molecular Geometry | trigonal planar |
| Hybridization Model | sp2 (central Se) |
| Bond Angle | 120° |
| Polarity | Nonpolar molecule |
The Se oxide Selenium trioxide is a key industrial intermediate. Nonmetal oxides such as SO3 and P4O10 are acid anhydrides for sulfuric and phosphoric acid manufacture, while metal/semimetal oxides are ceramics, refractories, catalysts and pigment precursors.
To draw the Selenium trioxide Lewis structure we first count the total valence electrons. O3Se contains 3×6 (O) + 6 (Se); the net charge of 0 gives a total of 24 valence electrons to place.
The central atom is Se. It is the least electronegative atom capable of forming multiple bonds and is surrounded by the more electronegative terminal atom(s); hydrogen, when present, always occupies a terminal position. Electronegativity considerations place the electron density toward the terminal atom(s).
Total valence electrons = 3×6 (O) + 6 (Se) = 24 electrons.
Place Se at the center and connect each surrounding atom with a single bond, complete octets on the terminal atoms, and place any remaining electrons on the central atom. The resulting electron distribution is: Se–O double bond, Se–O double bond and Se–O double bond; no lone pairs on Se.
Counting bonding and nonbonding electrons around Se therefore satisfies the octet/expanded-octet requirement for the drawn structure.
This species is best represented by resonance structures; the π bonding is delocalized over the equivalent terminal atom(s), so all Se–terminals bonds are equivalent in the resonance hybrid.
VSEPR theory states that the 3 electron domains around Se arrange to minimize mutual repulsion, giving an trigonal planar electron-domain geometry.
Because 0 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is trigonal planar; the Se bond angle is set to 120° rather than the ideal value for the electron-domain geometry.
A useful VSEPR approximation is: lone pair–lone pair repulsion > lone pair–bonding pair repulsion > bonding pair–bonding pair repulsion. With 0 lone pair(s) on Se, the lone-pair domains occupy positions that minimize overall repulsion while pushing the bonding domains (and therefore the bonded atoms) closer together.
In the conventional localized-bond model, Se uses sp2 hybrid orbitals to form the 3 equivalent electron-domain directions (3 bonding + 0 lone pair).
Formal charge on central Se = V − N − ½B = 6 − 0 − ½×12 = 0. The preferred Lewis structure carries zero formal charge on the central atom (and on the terminals), so it is the dominant contributor.
Selenium trioxide is nonpolar. Although individual Se–terminal bonds are polar when the atoms differ in electronegativity, the trigonal planar geometry makes their vector sum zero, so there is no net molecular dipole.
A common misconception is that polar bonds guarantee a polar molecule. Selenium trioxide shows the opposite: identical bond dipoles arranged with trigonal planar symmetry cancel exactly, yielding a nonpolar species.
Interpretation consistent with standard VSEPR / molecular-geometry references.Its nonpolar character governs solvation and intermolecular behavior; specify grade and handling when sourcing.
| Species | Formula | Central Atom | Electron Domains | Molecular Geometry | Polarity |
|---|---|---|---|---|---|
| Selenium trioxide | O3Se | Se | 3 | trigonal planar | Nonpolar |
| Selenium dioxide | O2Se | Se | 3 | bent | Polar |
| Hydrogen selenide | H2Se | Se | 4 | bent | Polar |
Selenium trioxide is nonpolar. Its trigonal planar symmetry cancels the bond dipoles exactly.
Se–O double bond, Se–O double bond and Se–O double bond; no lone pairs on Se. It uses all 24 valence electrons and the preferred structure carries zero formal charge on the central atom.
The Se angle is about 120°. Lone-pair repulsion compresses the angle from the ideal trigonal planar value.
The conventional model is sp2. Selenium trioxide has 3 electron domains around the central Se.
The CAS number is 13768-86-0. PubChem (CID 115128) and NIST identify this with O3Se; use it to locate suppliers and database records.
Technical scope: Lewis structures, VSEPR and hybridization are model-based descriptions for chemical communication and structure prediction; actual molecular electronic structure is more accurately represented by molecular-orbital and quantum-chemical methods. Commercial grades vary substantially by supplier and intended use; CAS 13768-86-0 identifies the substance, not a universal purity specification.
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