Allyl cation Lewis Structure

Allyl cation Lewis Structure: C₃H₅ Lewis Structure, tetrahedral Geometry, sp3 Hybridization & Polarity

Allyl cation Key Facts

The Allyl cation Lewis structure is C–C single bond and 3 C–H single bond; the central C has 4 electron domains (0 lone pairs), giving a tetrahedral electron-domain arrangement and a tetrahedral molecular geometry with a 109.5° bond angle. C is best described as sp3-hybridized, and Allyl cation is polar because the tetrahedral shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.

Figure 1: Lewis Structure of Allyl cation (C₃H₅)

Chemical Formula	C₃H₅
CAS Number	1724-80-1
Net Charge	+1
Total Valence Electrons	16
Lewis Structure	C–C single bond and 3 C–H single bond
Electron-Domain Geometry	tetrahedral
Molecular Geometry	tetrahedral
Hybridization Model	sp3 (central C)
Bond Angle	109.5°
Polarity	Polar molecule

PubChem and NIST list Allyl cation as C ₃H ₅ with CAS 1724-80-1; molecular weight ≈ None g/mol. View CAS 1724-80-1 dictionary details on Guidechem →

Applications of Allyl cation (CAS 1724-80-1)

In aqueous and process chemistry, C₃H₅ exists as the cation Allyl cation ion. It is encountered as a counterion and a controlled source of C in salts, buffers, electrochemistry and analytical protocols, and as a reactant in syntheses that require a defined equivalent of C-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 C in precipitation, complexation and redox procedures.

Procurement Note "Allyl cation" 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 1724-80-1 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Allyl cation Lewis structure we first count the total valence electrons. C₃H₅ contains 3×4 (C) + 5×1 (H) + 1 (net cation); the net charge of +1 gives a total of 16 valence electrons to place.

The central atom is C. 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 = 3×4 (C) + 5×1 (H) + 1 (net cation) = 16 electrons.

Step 2 - Lewis Structure & Electron Distribution

Place C 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: C–C single bond and 3 C–H single bond; no lone pairs on C.

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

C–C C–H ×3

C: 0 lone pairs, 4 bonding domains

4 bonding domains + 0 lone pairs = 4 electron domains

Octet Rule: Why C Has Eight Electrons C forms 4 bond(s) and retains 0 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 C arrange to minimize mutual repulsion, giving an tetrahedral electron-domain geometry.

Because 0 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is tetrahedral; the C bond angle is set to 109.5° 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 0 lone pair(s) on C, 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, C uses sp3 hybrid orbitals to form the 4 equivalent electron-domain directions (4 bonding + 0 lone pair).

Formal-charge check

Formal charge on central C = V − N − ½B = 4 − 0 − ½×8 = 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 C; full quantum-chemical treatments use molecular orbitals.

Is Allyl cation Polar or Nonpolar?

Allyl cation is polar. The tetrahedral 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 Allyl cation the tetrahedral 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
Allyl cation	C₃H₅	C	4	tetrahedral	Polar
Carbon dioxide	CO₂	C	2	linear	Nonpolar
Carbon monoxide	CO	C	2	linear (diatomic)	Polar
Carbon disulfide	CS₂	C	2	linear	Nonpolar
Methane	CH₄	C	4	tetrahedral	Nonpolar
Ethane	C₂H₆	C	4	tetrahedral	Nonpolar

Practice question Starting from the 16 valence electrons of C₃H₅, draw the Lewis structure and confirm the central C atom is sp3-hybridized with tetrahedral 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 Allyl cation (CAS 1724-80-1)? Browse Supplier on Guidechem →

FAQs

Is C₃H₅ polar or nonpolar?

Allyl cation is polar. Its tetrahedral geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.

What is the Lewis structure of Allyl cation?

C–C single bond and 3 C–H single bond; no lone pairs on C. It uses all 16 valence electrons and the preferred structure carries a formal charge of 3 on the central atom.

What is the bond angle in Allyl cation?

The C angle is about 109.5°. Lone-pair repulsion compresses the angle from the ideal tetrahedral value.

What is the hybridization of C in Allyl cation?

The conventional model is sp3. Allyl cation has 4 electron domains around the central C.

What is the CAS number of Allyl cation?

The CAS number is 1724-80-1. PubChem and NIST identify this with C₃H₅; use it to locate suppliers and database records.

References

PubChem, Allyl cation. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Allyl cation. 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 Allyl cation (CAS 1724-80-1).

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 1724-80-1 identifies the substance, not a universal purity specification.

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Allyl cation Lewis Structure

Allyl cation Lewis Structure