Aluminum hydride Lewis Structure

Aluminum hydride Lewis Structure: AlH₃ Lewis Structure, trigonal planar Geometry, sp2 Hybridization & Polarity

Aluminum hydride Key Facts

The Aluminum hydride Lewis structure is 3 Al–H single bond; the central Al has 3 electron domains (0 lone pairs), giving a trigonal planar electron-domain arrangement and a trigonal planar molecular geometry with a 120° bond angle. Al is best described as sp2-hybridized, and Aluminum hydride is nonpolar because the bond dipoles cancel by molecular symmetry.

Figure 1: Lewis Structure of Aluminum hydride (AlH₃)

Chemical Formula	AlH₃
CAS Number	7784-21-6
Total Valence Electrons	6
Lewis Structure	3 Al–H single bond
Electron-Domain Geometry	trigonal planar
Molecular Geometry	trigonal planar
Hybridization Model	sp2 (central Al)
Bond Angle	120°
Polarity	Nonpolar molecule

PubChem (CID 14488) and NIST list Aluminum hydride as AlH ₃ with CAS 7784-21-6; molecular weight ≈ 30.005 g/mol. View CAS 7784-21-6 dictionary details on Guidechem →

Applications of Aluminum hydride (CAS 7784-21-6)

Aluminum hydride 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 "Aluminum hydride" 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 7784-21-6 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Aluminum hydride Lewis structure we first count the total valence electrons. AlH₃ contains 3 (Al) + 3×1 (H); the net charge of 0 gives a total of 6 valence electrons to place.

The central atom is Al. 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 (Al) + 3×1 (H) = 6 electrons.

Step 2 - Lewis Structure & Electron Distribution

Place Al 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 Al–H single bond; no lone pairs on Al.

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

Al–H ×3

Al: 0 lone pairs, 3 bonding domains

3 bonding domains + 0 lone pairs = 3 electron domains

Octet Rule: Why Al Has Eight Electrons Al forms 3 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 3 electron domains around Al arrange to minimize mutual repulsion, giving an trigonal planar 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 trigonal planar; the Al bond angle is set to 120° 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 Al, 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, Al uses sp2 hybrid orbitals to form the 3 equivalent electron-domain directions (3 bonding + 0 lone pair).

Formal-charge check

Formal charge on central Al = V − N − ½B = 3 − 0 − 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: sp2 is a compact model for the 3 electron-domain directions around Al; full quantum-chemical treatments use molecular orbitals.

Is Aluminum hydride Polar or Nonpolar?

Aluminum hydride is nonpolar. Although individual Al–terminal bonds are polar when the atoms differ in electronegativity, the trigonal planar 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. Aluminum hydride shows the opposite: identical bond dipoles arranged with trigonal planar 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
Aluminum hydride	AlH₃	Al	3	trigonal planar	Nonpolar
Aluminum chloride	AlCl₃	Al	3	trigonal planar	Nonpolar

Practice question Starting from the 6 valence electrons of AlH₃, draw the Lewis structure and confirm the central Al atom is sp2-hybridized with trigonal planar 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 Aluminum hydride (CAS 7784-21-6)? Browse Supplier on Guidechem →

FAQs

Is AlH₃ polar or nonpolar?

Aluminum hydride is nonpolar. Its trigonal planar symmetry cancels the bond dipoles exactly.

What is the Lewis structure of Aluminum hydride?

3 Al–H single bond; no lone pairs on Al. It uses all 6 valence electrons and the preferred structure carries a formal charge of 3 on the central atom.

What is the bond angle in Aluminum hydride?

The Al angle is about 120°. Lone-pair repulsion compresses the angle from the ideal trigonal planar value.

What is the hybridization of Al in Aluminum hydride?

The conventional model is sp2. Aluminum hydride has 3 electron domains around the central Al.

What is the CAS number of Aluminum hydride?

The CAS number is 7784-21-6. PubChem (CID 14488) and NIST identify this with AlH₃; use it to locate suppliers and database records.

References

PubChem CID 14488, Aluminum hydride. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Aluminum hydride. 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 Aluminum hydride (CAS 7784-21-6).

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 7784-21-6 identifies the substance, not a universal purity specification.

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Aluminum hydride Lewis Structure