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The Metasilicate ion Lewis structure is Si–O single bond, Si–O double bond and Si–O single bond; the central Si 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. Si is best described as sp2-hybridized, and Metasilicate ion is nonpolar because the bond dipoles cancel by molecular symmetry.
Figure 1: Lewis Structure of Metasilicate ion (O3Si)
| Chemical Formula | O3Si |
| CAS Number | 15593-54-1 |
| Net Charge | -2 |
| Total Valence Electrons | 24 |
| Lewis Structure | Si–O single bond, Si–O double bond and Si–O single bond |
| Electron-Domain Geometry | trigonal planar |
| Molecular Geometry | trigonal planar |
| Hybridization Model | sp2 (central Si) |
| Bond Angle | 120° |
| Polarity | Nonpolar molecule |
In aqueous and process chemistry, O3Si exists as the anion Metasilicate ion ion. It is encountered as a counterion and a controlled source of Si in salts, buffers, electrochemistry and analytical protocols, and as a reactant in syntheses that require a defined equivalent of Si-containing material.
To draw the Metasilicate ion Lewis structure we first count the total valence electrons. O3Si contains 3×6 (O) + 4 (Si) − 2 (net anion); the net charge of -2 gives a total of 24 valence electrons to place.
The central atom is Si. 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) + 4 (Si) − 2 (net anion) = 24 electrons.
Place Si 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: Si–O single bond, Si–O double bond and Si–O single bond; no lone pairs on Si.
Counting bonding and nonbonding electrons around Si 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 Si–terminals bonds are equivalent in the resonance hybrid.
VSEPR theory states that the 3 electron domains around Si 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 Si 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 Si, 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, Si uses sp2 hybrid orbitals to form the 3 equivalent electron-domain directions (3 bonding + 0 lone pair).
Formal charge on central Si = V − N − ½B = 4 − 0 − ½×8 = 0. The preferred Lewis structure carries zero formal charge on the central atom (and on the terminals), so it is the dominant contributor.
Metasilicate ion is nonpolar. Although individual Si–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. Metasilicate ion 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 |
|---|---|---|---|---|---|
| Metasilicate ion | O3Si | Si | 3 | trigonal planar | Nonpolar |
| Silicon tetrafluoride | F4Si | Si | 4 | tetrahedral | Nonpolar |
| Silane | H4Si | Si | 4 | tetrahedral | Nonpolar |
Metasilicate ion is nonpolar. Its trigonal planar symmetry cancels the bond dipoles exactly.
Si–O single bond, Si–O double bond and Si–O single bond; no lone pairs on Si. It uses all 24 valence electrons and the preferred structure carries zero formal charge on the central atom.
The Si angle is about 120°. Lone-pair repulsion compresses the angle from the ideal trigonal planar value.
The conventional model is sp2. Metasilicate ion has 3 electron domains around the central Si.
The CAS number is 15593-54-1. PubChem and NIST identify this with O3Si; 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 15593-54-1 identifies the substance, not a universal purity specification.
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