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The Selenate ion Lewis structure is Se–O single bond, Se–O double bond, Se–O double bond and Se–O single bond; the central Se has 4 electron domains (0 lone pairs), giving a tetrahedral electron-domain arrangement and a tetrahedral molecular geometry with a 109.5° bond angle. Se is best described as sp3-hybridized, and Selenate ion is nonpolar because the bond dipoles cancel by molecular symmetry.
Figure 1: Lewis Structure of Selenate ion (O4Se-2)
| Chemical Formula | O4Se-2 |
| CAS Number | 14124-67-5 |
| Net Charge | -2 |
| Total Valence Electrons | 32 |
| Lewis Structure | Se–O single bond, Se–O double bond, Se–O double bond and Se–O single bond |
| Electron-Domain Geometry | tetrahedral |
| Molecular Geometry | tetrahedral |
| Hybridization Model | sp3 (central Se) |
| Bond Angle | 109.5° |
| Polarity | Nonpolar molecule |
In aqueous and process chemistry, O4Se-2 exists as the anion Selenate ion ion. It is encountered as a counterion and a controlled source of Se in salts, buffers, electrochemistry and analytical protocols, and as a reactant in syntheses that require a defined equivalent of Se-containing material.
To draw the Selenate ion Lewis structure we first count the total valence electrons. O4Se-2 contains 4×6 (O) + 6 (Se) − 2 (net anion); the net charge of -2 gives a total of 32 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 = 4×6 (O) + 6 (Se) − 2 (net anion) = 32 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 single bond, Se–O double bond, Se–O double bond and Se–O single 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 4 electron domains around Se arrange to minimize mutual repulsion, giving an tetrahedral 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 tetrahedral; the Se bond angle is set to 109.5° 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 sp3 hybrid orbitals to form the 4 equivalent electron-domain directions (4 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.
Selenate ion is nonpolar. Although individual Se–terminal bonds are polar when the atoms differ in electronegativity, the tetrahedral geometry makes their vector sum zero, so there is no net molecular dipole.
A common misconception is that polar bonds guarantee a polar molecule. Selenate ion shows the opposite: identical bond dipoles arranged with tetrahedral 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 |
|---|---|---|---|---|---|
| Selenate ion | O4Se-2 | Se | 4 | tetrahedral | Nonpolar |
| Selenium dioxide | O2Se | Se | 3 | bent | Polar |
| Hydrogen selenide | H2Se | Se | 4 | bent | Polar |
Selenate ion is nonpolar. Its tetrahedral symmetry cancels the bond dipoles exactly.
Se–O single bond, Se–O double bond, Se–O double bond and Se–O single bond; no lone pairs on Se. It uses all 32 valence electrons and the preferred structure carries zero formal charge on the central atom.
The Se angle is about 109.5°. Lone-pair repulsion compresses the angle from the ideal tetrahedral value.
The conventional model is sp3. Selenate ion has 4 electron domains around the central Se.
The CAS number is 14124-67-5. PubChem (CID 26473) and NIST identify this with O4Se-2; 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 14124-67-5 identifies the substance, not a universal purity specification.
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