Arsine Lewis Structure

Arsine Lewis Structure: AsH₃ Lewis Structure, trigonal pyramidal Geometry, sp3 Hybridization & Polarity

Arsine Key Facts

The Arsine Lewis structure is 3 As–H single bond; the central As has 4 electron domains (1 lone pair), giving a tetrahedral electron-domain arrangement and a trigonal pyramidal molecular geometry with a ≈107° bond angle. As is best described as sp3-hybridized, and Arsine is polar because the trigonal pyramidal shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.

Figure 1: Lewis Structure of Arsine (AsH₃)

Chemical Formula	AsH₃
CAS Number	7784-42-1
Total Valence Electrons	8
Lewis Structure	3 As–H single bond
Electron-Domain Geometry	tetrahedral
Molecular Geometry	trigonal pyramidal
Hybridization Model	sp3 (central As)
Bond Angle	≈107°
Polarity	Polar molecule

PubChem (CID 23969) and NIST list Arsine as AsH ₃ with CAS 7784-42-1; molecular weight ≈ 77.946 g/mol. View CAS 7784-42-1 dictionary details on Guidechem →

Applications of Arsine (CAS 7784-42-1)

As a hydride of As, Arsine is typically a strong reducing agent, a potential fuel component, or a precursor in inorganic and organometallic synthesis. Many pnictogen/sulfur hydrides are toxic, foul-smelling and pyrophoric or flammable, and are handled with appropriate ventilation and inert-atmosphere technique.

Reducing Agent Electron-rich hydrides reduce metal centers and functional groups in synthesis.

Precursor / Feedstock Source of As in the preparation of derivatives and doped materials.

Handling Often toxic/flammable/pyrophoric; inert atmosphere and active ventilation required.

Procurement Note "Arsine" 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 7784-42-1 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Arsine Lewis structure we first count the total valence electrons. AsH₃ contains 5 (As) + 3×1 (H); the net charge of 0 gives a total of 8 valence electrons to place.

The central atom is As. 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 = 5 (As) + 3×1 (H) = 8 electrons.

Step 2 - Lewis Structure & Electron Distribution

Place As 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: 3 As–H single bond; one lone pair on As.

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

As–H ×3

As: 1 lone pair, 3 bonding domains

3 bonding domains + 1 lone pairs = 4 electron domains

Octet Rule: Why As Has Eight Electrons As forms 3 bond(s) and retains 2 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 As arrange to minimize mutual repulsion, giving an tetrahedral electron-domain geometry.

Because 1 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is trigonal pyramidal; the As bond angle is set to ≈107° 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 1 lone pair(s) on As, 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, As uses sp3 hybrid orbitals to form the 4 equivalent electron-domain directions (3 bonding + 1 lone pair).

Formal-charge check

Formal charge on central As = V − N − ½B = 5 − 2 − ½×6 = 3. 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 As; full quantum-chemical treatments use molecular orbitals.

Is Arsine Polar or Nonpolar?

Arsine is polar. The trigonal pyramidal 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 Arsine the trigonal pyramidal 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
Arsine	AsH₃	As	4	trigonal pyramidal	Polar
Arsenic trifluoride	AsF₃	As	4	trigonal pyramidal	Polar

Practice question Starting from the 8 valence electrons of AsH₃, draw the Lewis structure and confirm the central As atom is sp3-hybridized with trigonal pyramidal 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 Arsine (CAS 7784-42-1)? Browse Supplier on Guidechem →

FAQs

Is AsH₃ polar or nonpolar?

Arsine is polar. Its trigonal pyramidal geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.

What is the Lewis structure of Arsine?

3 As–H single bond; one lone pair on As. It uses all 8 valence electrons and the preferred structure carries a formal charge of 3 on the central atom.

What is the bond angle in Arsine?

The As angle is about ≈107°. Lone-pair repulsion compresses the angle from the ideal tetrahedral value.

What is the hybridization of As in Arsine?

The conventional model is sp3. Arsine has 4 electron domains around the central As.

What is the CAS number of Arsine?

The CAS number is 7784-42-1. PubChem (CID 23969) and NIST identify this with AsH₃; use it to locate suppliers and database records.

References

PubChem CID 23969, Arsine. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Arsine. 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 Arsine (CAS 7784-42-1).

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 7784-42-1 identifies the substance, not a universal purity specification.

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Arsine Lewis Structure

Arsine Lewis Structure