Tribromide ion Lewis Structure

Tribromide ion Lewis Structure: Br₃ Lewis Structure, linear Geometry, sp3d Hybridization & Polarity

Tribromide ion Key Facts

The Tribromide ion Lewis structure is Br–Br single bond and Br–Br single bond; the central Br has 5 electron domains (3 lone pairs), giving a trigonal bipyramidal electron-domain arrangement and a linear molecular geometry with a 180° bond angle. Br is best described as sp3d-hybridized, and Tribromide ion is nonpolar because the bond dipoles cancel by molecular symmetry.

Figure 1: Lewis Structure of Tribromide ion (Br₃)

Chemical Formula	Br₃
CAS Number	24929-17-3
Net Charge	-1
Total Valence Electrons	22
Lewis Structure	Br–Br single bond and Br–Br single bond
Electron-Domain Geometry	trigonal bipyramidal
Molecular Geometry	linear
Hybridization Model	sp3d (central Br)
Bond Angle	180°
Polarity	Nonpolar molecule

PubChem and NIST list Tribromide ion as Br ₃ with CAS 24929-17-3; molecular weight ≈ None g/mol. View CAS 24929-17-3 dictionary details on Guidechem →

Applications of Tribromide ion (CAS 24929-17-3)

In aqueous and process chemistry, Br₃ exists as the anion Tribromide ion ion. It is encountered as a counterion and a controlled source of Br in salts, buffers, electrochemistry and analytical protocols, and as a reactant in syntheses that require a defined equivalent of Br-containing material.

Ion Source / Counterion Supplied as salts and solutions; specify hydration, counter-cation and concentration.

Analytical & Electrochemical Used in titrations, plating baths and ionic-strength control where the ion is the active species.

Synthesis Reagent A controlled source of Br in precipitation, complexation and redox procedures.

Procurement Note "Tribromide ion" is supplied in multiple commercial grades and package sizes. Specify purity, grade, moisture/impurity limits, package (cylinder, drum or bulk) and intended process, and use CAS 24929-17-3 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Tribromide ion Lewis structure we first count the total valence electrons. Br₃ contains 3×7 (Br) − 1 (net anion); the net charge of -1 gives a total of 22 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).

Valence-electron count

Total valence electrons = 3×7 (Br) − 1 (net anion) = 22 electrons.

Step 2 - Lewis Structure & Electron Distribution

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–Br single bond and Br–Br single bond; 3 lone pairs on Br.

Counting bonding and nonbonding electrons around Br therefore satisfies the octet/expanded-octet requirement for the drawn structure.

Br–Br Br–Br

Br: 3 lone pairs, 2 bonding domains

2 bonding domains + 3 lone pairs = 5 electron domains

Expanded Octet: d-Orbital Participation Central Br belongs to period 3 or below, so it can accommodate more than eight electrons: low-lying d orbitals become available and the linear arrangement with 5 domains reflects this expanded valence shell. The octet rule alone does not apply to such hypervalent species.

Step 3 - VSEPR Theory & Geometry

VSEPR theory states that the 5 electron domains around Br arrange to minimize mutual repulsion, giving an trigonal bipyramidal electron-domain geometry.

Because 3 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is linear; the Br bond angle is set to 180° rather than the ideal value for the electron-domain geometry.

Repulsion hierarchy

A useful VSEPR approximation is: lone pair–lone pair repulsion > lone pair–bonding pair repulsion > bonding pair–bonding pair repulsion. With 3 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.

Hybridization & Formal Charge

In the conventional localized-bond model, Br uses sp3d hybrid orbitals to form the 5 equivalent electron-domain directions (2 bonding + 3 lone pair).

Formal-charge check

Formal charge on central Br = V − N − ½B = 7 − 6 − ½×4 = -1. The nonzero formal charge is distributed by resonance / charge separation; the drawn structure is the lowest-energy contributor.

Modeling Note Modeling Note: sp3d / sp3d hybridization is a convenient localized-bond teaching model. Modern quantum-chemical descriptions of hypervalent Tribromide ion use molecular orbitals and do not require populated d orbitals as the primary bonding picture.

Is Tribromide ion Polar or Nonpolar?

Tribromide ion is nonpolar. Although individual Br–terminal bonds are polar when the atoms differ in electronegativity, the linear geometry makes their vector sum zero, so there is no net molecular dipole.

Expert Quote — Structural Chemistry Perspective

A common misconception is that polar bonds guarantee a polar molecule. Tribromide ion shows the opposite: identical bond dipoles arranged with linear 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.

Structural Comparison Table

Species	Formula	Central Atom	Electron Domains	Molecular Geometry	Polarity
Tribromide ion	Br₃	Br	5	linear	Nonpolar
Bromine trifluoride	BrF₃	Br	5	T-shaped	Polar
Hydrogen bromide	HBr	Br	4	linear (diatomic)	Polar

Practice question Starting from the 22 valence electrons of Br₃, draw the Lewis structure and confirm the central Br atom is sp3d-hybridized with linear geometry. What happens to the bond angle if one terminal atom is replaced by a more electronegative substituent?

Looking for industrial bulk or specified-grade supplies of Tribromide ion (CAS 24929-17-3)? Browse Supplier on Guidechem →

FAQs

Is Br₃ polar or nonpolar?

Tribromide ion is nonpolar. Its linear symmetry cancels the bond dipoles exactly.

What is the Lewis structure of Tribromide ion?

Br–Br single bond and Br–Br single bond; 3 lone pairs on Br. It uses all 22 valence electrons and the preferred structure carries a formal charge of -1 on the central atom.

What is the bond angle in Tribromide ion?

The Br angle is about 180°. Lone-pair repulsion compresses the angle from the ideal trigonal bipyramidal value.

What is the hybridization of Br in Tribromide ion?

The conventional model is sp3d. Tribromide ion has 5 electron domains around the central Br.

What is the CAS number of Tribromide ion?

The CAS number is 24929-17-3. PubChem and NIST identify this with Br₃; use it to locate suppliers and database records.

References

PubChem, Tribromide ion. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Tribromide ion. Formula, CAS Registry Number and thermochemical / spectroscopic data.
IUPAC Gold Book. Definitions for "lone pair", "VSEPR", "hybridization" and "formal charge".
Atkins, P. & de Paula, J., Physical Chemistry. VSEPR, molecular geometry and dipole moments.
Guidechem supplier & dictionary records. Commercial sourcing and CAS-linked property pages for Tribromide ion (CAS 24929-17-3).

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 24929-17-3 identifies the substance, not a universal purity specification.

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Tribromide ion Lewis Structure

Tribromide ion Lewis Structure