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The Iodine tribromide Lewis structure is I–Br single bond, I–Br single bond and I–Br single bond; the central I has 5 electron domains (2 lone pairs), giving a trigonal bipyramidal electron-domain arrangement and a T-shaped molecular geometry with a ≈87.5° bond angle. I is best described as sp3d-hybridized, and Iodine tribromide is polar because the T-shaped shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.
Figure 1: Lewis Structure of Iodine tribromide (Br3I)
| Chemical Formula | Br3I |
| CAS Number | 7789-58-4 |
| Total Valence Electrons | 28 |
| Lewis Structure | I–Br single bond, I–Br single bond and I–Br single bond |
| Electron-Domain Geometry | trigonal bipyramidal |
| Molecular Geometry | T-shaped |
| Hybridization Model | sp3d (central I) |
| Bond Angle | ≈87.5° |
| Polarity | Polar molecule |
Iodine tribromide 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 Iodine tribromide Lewis structure we first count the total valence electrons. Br3I contains 3×7 (Br) + 7 (I); the net charge of 0 gives a total of 28 valence electrons to place.
The central atom is I. 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 = 3×7 (Br) + 7 (I) = 28 electrons.
Place I 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: I–Br single bond, I–Br single bond and I–Br single bond; 2 lone pairs on I.
Counting bonding and nonbonding electrons around I therefore satisfies the octet/expanded-octet requirement for the drawn structure.
VSEPR theory states that the 5 electron domains around I arrange to minimize mutual repulsion, giving an trigonal bipyramidal 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 T-shaped; the I bond angle is set to ≈87.5° 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 I, 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, I uses sp3d hybrid orbitals to form the 5 equivalent electron-domain directions (3 bonding + 2 lone pair).
Formal charge on central I = 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.
Iodine tribromide is polar. The T-shaped 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 Iodine tribromide the T-shaped 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 |
|---|---|---|---|---|---|
| Iodine tribromide | Br3I | I | 5 | T-shaped | Polar |
| Iodine trifluoride | IF3 | I | 5 | T-shaped | Polar |
| Iodine pentafluoride | IF5 | I | 6 | square pyramidal | Polar |
| Iodine heptafluoride | IF7 | I | 7 | pentagonal bipyramidal | Nonpolar |
| Iodine | I2 | I | 4 | linear (diatomic) | Nonpolar |
| Hydrogen iodide | HI | I | 4 | linear (diatomic) | Polar |
Iodine tribromide is polar. Its T-shaped geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.
I–Br single bond, I–Br single bond and I–Br single bond; 2 lone pairs on I. It uses all 28 valence electrons and the preferred structure carries zero formal charge on the central atom.
The I angle is about ≈87.5°. Lone-pair repulsion compresses the angle from the ideal trigonal bipyramidal value.
The conventional model is sp3d. Iodine tribromide has 5 electron domains around the central I.
The CAS number is 7789-58-4. PubChem (CID 5187573) and NIST identify this with Br3I; 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 7789-58-4 identifies the substance, not a universal purity specification.
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