Iodide ion Lewis Structure

Iodide ion Lewis Structure: I^- Lewis Structure, see text Geometry, sp3 Hybridization & Polarity

Iodide ion Key Facts

The Iodide ion Lewis structure is central I bonded; the central I has 4 electron domains (4 lone pairs), giving a tetrahedral electron-domain arrangement and a see text molecular geometry with a — bond angle. I is best described as sp3-hybridized, and Iodide ion is polar because the see text shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.

Figure 1: Lewis Structure of Iodide ion (I^-)

Chemical Formula	I^-
CAS Number	20461-54-5
Net Charge	-1
Total Valence Electrons	8
Lewis Structure	central I bonded
Electron-Domain Geometry	tetrahedral
Molecular Geometry	see text
Hybridization Model	sp3 (central I)
Bond Angle	—
Polarity	Polar molecule

PubChem (CID 30165) and NIST list Iodide ion as I ^- with CAS 20461-54-5; molecular weight ≈ 126.9045 g/mol. View CAS 20461-54-5 dictionary details on Guidechem →

Applications of Iodide ion (CAS 20461-54-5)

In aqueous and process chemistry, I^- exists as the anion Iodide ion ion. It is encountered as a counterion and a controlled source of I in salts, buffers, electrochemistry and analytical protocols, and as a reactant in syntheses that require a defined equivalent of I-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 I in precipitation, complexation and redox procedures.

Procurement Note "Iodide 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 20461-54-5 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Iodide ion Lewis structure we first count the total valence electrons. I^- contains 7 (I) − 1 (net anion); the net charge of -1 gives a total of 8 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).

Valence-electron count

Total valence electrons = 7 (I) − 1 (net anion) = 8 electrons.

Step 2 - Lewis Structure & Electron Distribution

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: central I bonded; 4 lone pairs on I.

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

I: 4 lone pairs, 0 bonding domains

0 bonding domains + 4 lone pairs = 4 electron domains

Octet Rule: Why I Has Eight Electrons I forms 0 bond(s) and retains 8 nonbonding electron(s), reaching an octet. No expanded octet is required for this second-row (or octet-satisfying) central atom.

Step 3 - VSEPR Theory & Geometry

VSEPR theory states that the 4 electron domains around I arrange to minimize mutual repulsion, giving an tetrahedral electron-domain geometry.

Because 4 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is see text; the I bond angle is set to — 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 4 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.

Hybridization & Formal Charge

In the conventional localized-bond model, I uses sp3 hybrid orbitals to form the 4 equivalent electron-domain directions (0 bonding + 4 lone pair).

Formal-charge check

Formal charge on central I = V − N − ½B = 7 − 8 − ½×0 = -1. The nonzero formal charge is distributed by resonance / charge separation; the drawn structure is the lowest-energy contributor.

Modeling Note Modeling Note: sp3 is a compact model for the 4 electron-domain directions around I; full quantum-chemical treatments use molecular orbitals.

Is Iodide ion Polar or Nonpolar?

Iodide ion is polar. The see text 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.

Expert Quote — Structural Chemistry Perspective

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 Iodide ion the see text 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.

Structural Comparison Table

Species	Formula	Central Atom	Electron Domains	Molecular Geometry	Polarity
Iodide ion	I^-	I	4	see text	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

Practice question Starting from the 8 valence electrons of I^-, draw the Lewis structure and confirm the central I atom is sp3-hybridized with see text 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 Iodide ion (CAS 20461-54-5)? Browse Supplier on Guidechem →

FAQs

Is I^- polar or nonpolar?

Iodide ion is polar. Its see text geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.

What is the Lewis structure of Iodide ion?

central I bonded; 4 lone pairs on I. It uses all 8 valence electrons and the preferred structure carries a formal charge of -1 on the central atom.

What is the bond angle in Iodide ion?

The I angle is about —. Lone-pair repulsion compresses the angle from the ideal tetrahedral value.

What is the hybridization of I in Iodide ion?

The conventional model is sp3. Iodide ion has 4 electron domains around the central I.

What is the CAS number of Iodide ion?

The CAS number is 20461-54-5. PubChem (CID 30165) and NIST identify this with I^-; use it to locate suppliers and database records.

References

PubChem CID 30165, Iodide ion. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Iodide 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 Iodide ion (CAS 20461-54-5).

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 20461-54-5 identifies the substance, not a universal purity specification.

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Iodide ion Lewis Structure