Borohydride ion Lewis Structure

Borohydride ion Lewis Structure: BH₄Na Lewis Structure, tetrahedral Geometry, sp3 Hybridization & Polarity

Borohydride ion Key Facts

The Borohydride ion Lewis structure is 4 B–H single bond; the central B has 4 electron domains (0 lone pairs), giving a tetrahedral electron-domain arrangement and a tetrahedral molecular geometry with a 109.5° bond angle. B is best described as sp3-hybridized, and Borohydride ion is nonpolar because the bond dipoles cancel by molecular symmetry.

Figure 1: Lewis Structure of Borohydride ion (BH₄Na)

Chemical Formula	BH₄Na
CAS Number	16940-66-2
Total Valence Electrons	8
Lewis Structure	4 B–H single bond
Electron-Domain Geometry	tetrahedral
Molecular Geometry	tetrahedral
Hybridization Model	sp3 (central B)
Bond Angle	109.5°
Polarity	Nonpolar molecule

PubChem (CID 4311764) and NIST list Borohydride ion as BH ₄Na with CAS 16940-66-2; molecular weight ≈ 37.84 g/mol. View CAS 16940-66-2 dictionary details on Guidechem →

Applications of Borohydride ion (CAS 16940-66-2)

As a hydride of B, Borohydride ion 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 B in the preparation of derivatives and doped materials.

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

Procurement Note "Borohydride 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 16940-66-2 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Borohydride ion Lewis structure we first count the total valence electrons. BH₄Na contains 3 (B) + 4×1 (H) + 1 (Na); the net charge of 0 gives a total of 8 valence electrons to place.

The central atom is B. 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 (B) + 4×1 (H) + 1 (Na) = 8 electrons.

Step 2 - Lewis Structure & Electron Distribution

Place B 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: 4 B–H single bond; no lone pairs on B.

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

B–H ×4

B: 0 lone pairs, 4 bonding domains

4 bonding domains + 0 lone pairs = 4 electron domains

Octet Rule: Why B Has Eight Electrons B 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 B 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 B 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 B, 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, B uses sp3 hybrid orbitals to form the 4 equivalent electron-domain directions (4 bonding + 0 lone pair).

Formal-charge check

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

Is Borohydride ion Polar or Nonpolar?

Borohydride ion is nonpolar. Although individual B–terminal bonds are polar when the atoms differ in electronegativity, the tetrahedral 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. Borohydride ion shows the opposite: identical bond dipoles arranged with tetrahedral 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
Borohydride ion	BH₄Na	B	4	tetrahedral	Nonpolar
Boron trifluoride	BF₃	B	3	trigonal planar	Nonpolar
Boron trichloride	BCl₃	B	3	trigonal planar	Nonpolar
Diborane	B₂H₆	B	3	trigonal planar	Polar

Practice question Starting from the 8 valence electrons of BH₄Na, draw the Lewis structure and confirm the central B 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 Borohydride ion (CAS 16940-66-2)? Browse Supplier on Guidechem →

FAQs

Is BH₄Na polar or nonpolar?

Borohydride ion is nonpolar. Its tetrahedral symmetry cancels the bond dipoles exactly.

What is the Lewis structure of Borohydride ion?

4 B–H single bond; no lone pairs on B. 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 Borohydride ion?

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

What is the hybridization of B in Borohydride ion?

The conventional model is sp3. Borohydride ion has 4 electron domains around the central B.

What is the CAS number of Borohydride ion?

The CAS number is 16940-66-2. PubChem (CID 4311764) and NIST identify this with BH₄Na; use it to locate suppliers and database records.

References

PubChem CID 4311764, Borohydride ion. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Borohydride 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 Borohydride ion (CAS 16940-66-2).

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 16940-66-2 identifies the substance, not a universal purity specification.

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Borohydride ion Lewis Structure

Borohydride ion Lewis Structure