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The Boron hydride radical (BH₂) Lewis structure is 2 B–H single bond; the central B has 3 electron domains (0 lone pairs), giving a trigonal planar electron-domain arrangement and a bent molecular geometry with a ≈119° bond angle. B is best described as sp2-hybridized, and Boron hydride radical (BH₂) is polar because the bent shape (and/or unequal terminal atoms) prevents cancellation of the bond dipoles.
Figure 1: Lewis Structure of Boron hydride radical (BH₂) (H2B)
| Chemical Formula | H2B |
| CAS Number | 13763-97-8 |
| Total Valence Electrons | 5 |
| Lewis Structure | 2 B–H single bond |
| Electron-Domain Geometry | trigonal planar |
| Molecular Geometry | bent |
| Hybridization Model | sp2 (central B) |
| Bond Angle | ≈119° |
| Polarity | Polar molecule |
As a hydride of B, Boron hydride radical (BH₂) 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.
To draw the Boron hydride radical (BH₂) Lewis structure we first count the total valence electrons. H2B contains 2×1 (H) + 3 (B); the net charge of 0 gives a total of 5 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).
Total valence electrons = 2×1 (H) + 3 (B) = 5 electrons.
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: 2 B–H single bond; no lone pairs on B and one unpaired electron on B.
Counting bonding and nonbonding electrons around B therefore satisfies the octet/expanded-octet requirement for the drawn structure.
VSEPR theory states that the 3 electron domains around B 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 bent; the B bond angle is set to ≈119° rather than the ideal value for the electron-domain geometry.
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.
In the conventional localized-bond model, B uses sp2 hybrid orbitals to form the 3 equivalent electron-domain directions (2 bonding + 0 lone pair).
Formal charge on central B = V − N − ½B = 3 − 0 − ½×4 = 3. The nonzero formal charge is distributed by resonance / charge separation; the drawn structure is the lowest-energy contributor.
Boron hydride radical (BH₂) is polar. The bent 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.
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 Boron hydride radical (BH₂) the bent 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.
| Species | Formula | Central Atom | Electron Domains | Molecular Geometry | Polarity |
|---|---|---|---|---|---|
| Boron hydride radical (BH₂) | H2B | B | 3 | bent | Polar |
| Boron trifluoride | BF3 | B | 3 | trigonal planar | Nonpolar |
| Boron trichloride | BCl3 | B | 3 | trigonal planar | Nonpolar |
| Diborane | B2H6 | B | 3 | trigonal planar | Polar |
Boron hydride radical (BH₂) is polar. Its bent geometry (and/or unequal terminal atoms) stops the bond dipoles from cancelling.
2 B–H single bond; no lone pairs on B and one unpaired electron on B. It uses all 5 valence electrons and the preferred structure carries a formal charge of 3 on the central atom.
The B angle is about ≈119°. Lone-pair repulsion compresses the angle from the ideal trigonal planar value.
The conventional model is sp2. Boron hydride radical (BH₂) has 3 electron domains around the central B.
The CAS number is 13763-97-8. PubChem and NIST identify this with H2B; use it to locate suppliers and database records.
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 13763-97-8 identifies the substance, not a universal purity specification.
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