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The Arsenic dioxide Lewis structure is As–O double bond and As–O single bond; the central As has 3 electron domains (1 lone pair), giving a trigonal planar electron-domain arrangement and a bent molecular geometry with a ≈119° bond angle. As is best described as sp2-hybridized, and Arsenic dioxide is polar because the bent shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.
Figure 1: Lewis Structure of Arsenic dioxide (As2O4)
| Chemical Formula | As2O4 |
| CAS Number | 12255-12-6 |
| Total Valence Electrons | 34 |
| Lewis Structure | As–O double bond and As–O single bond |
| Electron-Domain Geometry | trigonal planar |
| Molecular Geometry | bent |
| Hybridization Model | sp2 (central As) |
| Bond Angle | ≈119° |
| Polarity | Polar molecule |
The As oxide Arsenic dioxide 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 Arsenic dioxide Lewis structure we first count the total valence electrons. As2O4 contains 2×5 (As) + 4×6 (O); the net charge of 0 gives a total of 34 valence electrons to place.
The central atom is As. 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 = 2×5 (As) + 4×6 (O) = 34 electrons.
Place As 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: As–O double bond and As–O single bond; one lone pair on As.
Counting bonding and nonbonding electrons around As 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 As–terminals bonds are equivalent in the resonance hybrid.
VSEPR theory states that the 3 electron domains around As arrange to minimize mutual repulsion, giving an trigonal planar electron-domain geometry.
Because 1 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is bent; the As bond angle is set to ≈119° 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 1 lone pair(s) on As, 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, As uses sp2 hybrid orbitals to form the 3 equivalent electron-domain directions (2 bonding + 1 lone pair).
Formal charge on central As = V − N − ½B = 5 − 2 − ½×6 = 0. The preferred Lewis structure carries zero formal charge on the central atom (and on the terminals), so it is the dominant contributor.
Arsenic dioxide is polar. The bent shape prevents cancellation of the bond dipoles. The bond dipoles do not cancel, leaving a net molecular dipole, which strongly influences solvation behavior and intermolecular interactions.
The decisive structural fact is not simply that the individual bonds are polar; it is whether molecular symmetry allows their vector sum to vanish. In Arsenic dioxide the bent arrangement prevents cancellation, so a permanent dipole remains.
Interpretation consistent with standard VSEPR / molecular-geometry references.This polarity profile underpins its behavior as a solvent, reactant or process intermediate; when sourcing, specify grade and container compatibility.
| Species | Formula | Central Atom | Electron Domains | Molecular Geometry | Polarity |
|---|---|---|---|---|---|
| Arsenic dioxide | As2O4 | As | 3 | bent | Polar |
| Arsenic trifluoride | AsF3 | As | 4 | trigonal pyramidal | Polar |
Arsenic dioxide is polar. Its bent geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.
As–O double bond and As–O single bond; one lone pair on As. It uses all 34 valence electrons and the preferred structure carries zero formal charge on the central atom.
The As angle is about ≈119°. Lone-pair repulsion compresses the angle from the ideal trigonal planar value.
The conventional model is sp2. Arsenic dioxide has 3 electron domains around the central As.
The CAS number is 12255-12-6. PubChem (CID 154733448) and NIST identify this with As2O4; 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 12255-12-6 identifies the substance, not a universal purity specification.
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