Hydrogen iodide Lewis Structure

Hydrogen iodide Lewis Structure: HI Lewis Structure, linear (diatomic) Geometry, sp3 Hybridization & Polarity

Hydrogen iodide Key Facts

The Hydrogen iodide Lewis structure is a linear diatomic with a polar bond between its two atoms; because the two atoms differ in electronegativity, Hydrogen iodide is polar.

Figure 1: Lewis Structure of Hydrogen iodide (HI)

Chemical Formula	HI
CAS Number	10034-85-2
Total Valence Electrons	8
Lewis Structure	linear diatomic molecule with one single bond
Electron-Domain Geometry	linear
Molecular Geometry	linear (diatomic)
Hybridization Model	sp3
Bond Angle	180°
Polarity	Polar molecule

PubChem (CID 24841) and NIST list Hydrogen iodide as HI with CAS 10034-85-2; molecular weight ≈ 127.9124 g/mol. View CAS 10034-85-2 dictionary details on Guidechem →

Applications of Hydrogen iodide (CAS 10034-85-2)

Hydrogen iodide 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.

Reagent / Intermediate Used in synthesis and formulation where the substance's reactivity is required.

Specialty Chemical Specified by grade for the intended process or research use.

Sourcing Verify purity, package and regional availability via the CAS identifier.

Procurement Note "Hydrogen iodide" 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 10034-85-2 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Hydrogen iodide Lewis structure we first count the total valence electrons. HI contains 1 (H) + 7 (I); the net charge of 0 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 = 1 (H) + 7 (I) = 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: linear diatomic molecule with one single bond; 3 lone pair(s) on I.

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

I–H

I: 3 lone pairs, 1 bonding domain

1 bonding domains + 3 lone pairs = 4 electron domains

Octet & Diradical Note In a simple Lewis drawing each atom of this homonuclear diatomic carries lone pairs; species such as O₂ are more accurately described by molecular-orbital theory (paramagnetism arises from unpaired electrons in π* orbitals).

Step 3 - VSEPR Theory & Geometry

VSEPR theory states that the 4 electron domains around I arrange to minimize mutual repulsion, giving an linear 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 (diatomic); the I 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 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 (1 bonding + 3 lone pair).

Formal-charge check

Formal charge on central I = V − N − ½B = 7 − 6 − ½×2 = 0. The preferred Lewis structure carries zero formal charge on the central atom (and on the terminals), so it is the dominant 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 Hydrogen iodide Polar or Nonpolar?

Hydrogen iodide is polar. The linear (diatomic) 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 Hydrogen iodide the linear (diatomic) 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
Hydrogen iodide	HI	I	4	linear (diatomic)	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

Practice question Starting from the 8 valence electrons of HI, draw the Lewis structure and confirm the central I atom is sp3-hybridized with linear (diatomic) 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 Hydrogen iodide (CAS 10034-85-2)? Browse Supplier on Guidechem →

FAQs

Is HI polar or nonpolar?

Hydrogen iodide is polar. Its linear (diatomic) geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.

What is the Lewis structure of Hydrogen iodide?

linear diatomic molecule with one single bond; 3 lone pair(s) on I. It uses all 8 valence electrons and the preferred structure carries zero formal charge on the central atom.

What is the bond angle in Hydrogen iodide?

The I angle is about 180°. Lone-pair repulsion compresses the angle from the ideal linear value.

What is the hybridization of I in Hydrogen iodide?

The conventional model is sp3. Hydrogen iodide has 4 electron domains around the central I.

What is the CAS number of Hydrogen iodide?

The CAS number is 10034-85-2. PubChem (CID 24841) and NIST identify this with HI; use it to locate suppliers and database records.

References

PubChem CID 24841, Hydrogen iodide. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Hydrogen iodide. 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 Hydrogen iodide (CAS 10034-85-2).

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 10034-85-2 identifies the substance, not a universal purity specification.

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Hydrogen iodide Lewis Structure