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The Bromous acid Lewis structure is Br–O single bond and Br–O double bond; the central Br has 4 electron domains (2 lone pairs), giving a tetrahedral electron-domain arrangement and a bent molecular geometry with a ≈104.5° bond angle. Br is best described as sp3-hybridized, and Bromous acid is polar because the bent shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.
Figure 1: Lewis Structure of Bromous acid (BrHO2)
| Chemical Formula | BrHO2 |
| CAS Number | 37691-27-3 |
| Total Valence Electrons | 20 |
| Lewis Structure | Br–O single bond and Br–O double bond |
| Electron-Domain Geometry | tetrahedral |
| Molecular Geometry | bent |
| Hybridization Model | sp3 (central Br) |
| Bond Angle | ≈104.5° |
| Polarity | Polar molecule |
Bromous acid is encountered as a reagent, intermediate or specialty chemical in inorganic, organometallic and materials synthesis. Confirm grade, purity and supplier documentation (SDS) before specifying for a process.
To draw the Bromous acid Lewis structure we first count the total valence electrons. BrHO2 contains 7 (Br) + 1 (H) + 2×6 (O); the net charge of 0 gives a total of 20 valence electrons to place.
The central atom is Br. 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 = 7 (Br) + 1 (H) + 2×6 (O) = 20 electrons.
Place Br 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: Br–O single bond and Br–O double bond; 2 lone pairs on Br.
Counting bonding and nonbonding electrons around Br 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 Br–terminals bonds are equivalent in the resonance hybrid.
VSEPR theory states that the 4 electron domains around Br arrange to minimize mutual repulsion, giving an tetrahedral electron-domain geometry.
Because 2 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is bent; the Br bond angle is set to ≈104.5° 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 2 lone pair(s) on Br, 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, Br uses sp3 hybrid orbitals to form the 4 equivalent electron-domain directions (2 bonding + 2 lone pair).
Formal charge on central Br = V − N − ½B = 7 − 4 − 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.
Bromous acid 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 Bromous acid 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 |
|---|---|---|---|---|---|
| Bromous acid | BrHO2 | Br | 4 | bent | Polar |
| Bromine trifluoride | BrF3 | Br | 5 | T-shaped | Polar |
| Hydrogen bromide | HBr | Br | 4 | linear (diatomic) | Polar |
Bromous acid is polar. Its bent geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.
Br–O single bond and Br–O double bond; 2 lone pairs on Br. It uses all 20 valence electrons and the preferred structure carries zero formal charge on the central atom.
The Br angle is about ≈104.5°. Lone-pair repulsion compresses the angle from the ideal tetrahedral value.
The conventional model is sp3. Bromous acid has 4 electron domains around the central Br.
The CAS number is 37691-27-3. PubChem (CID 165616) and NIST identify this with BrHO2; 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 37691-27-3 identifies the substance, not a universal purity specification.
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