Chem Explorers

BH3: Exploring the Trigonal Planar Geometry and Nonpolar Nature

The Lewis Structure of BH3

In chemistry, Lewis structures are diagrams that show the bonding between atoms of a molecule. They are used to represent the valence electrons of atoms which participate in chemical bonding.

In the case of BH3, the central atom is Boron, and the three Hydrogens atoms are connected to it.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. They are involved in chemical reactions and bonding.

Boron has three valence electrons while hydrogen has one. Therefore, BH3 has three valence electrons in the central atom and three valence electrons from the Hydrogen atoms.

Determining the Central Atom

The central atom in a molecule is the atom that directly bonds with other atoms. In the case of BH3, Boron is the central atom.

Boron has a lower electronegativity than Hydrogen, which makes it more likely to bond with other atoms.

Connecting Outer Atoms to Central Atom

Once the central atom is determined, the next step is to connect the outer atoms. The three Hydrogen atoms are then connected to Boron, forming a three-legged structure.

Octet of All Atoms

In most cases, atoms will seek to achieve an electron configuration with an octet of electrons in their valence shell. An octet is a set of eight electrons in the outermost shell of an atom.

In the Lewis structure of BH3, the central Boron atom only has six valence electrons. On the other hand, Hydrogen atoms complete their octet with only two electrons.

Formal Charge Calculation

Formal charge is a method used to determine the distribution of electrons in a molecule. It is a way of determining how much negative or positive charge an atom has in a molecule.

For BH3, the formal charge is calculated as follows:

Formal charge = Valence electron – Number of bonds – Number of non-bonding electrons

For Boron: Formal Charge = 3 – 3 – 0 = 0

For Hydrogen: Formal Charge = 1 – 1 – 0 = 0

The formal charges of all the atoms are zero in this case, which indicates that all atoms are neutral.

BH3 Lewis Structure

Combining all the above steps, we can now draw the Lewis structure of BH3. The central Boron atom is surrounded by three Hydrogen atoms forming a trigonal planar shape.

Boron is connected to each Hydrogen atom by a single bond. The Lewis structure of BH3 shows that each atom achieves an octet of electrons, and the formal charge of each atom is zero.

Electron and Molecular Geometry of BH3

VSEPR Theory Explanation

The Valence Shell Electron Pair Repulsion (VSEPR) theory explains the three-dimensional arrangement of atoms around a central atom in a molecule. It is based on the assumption that electron pairs will repel one another and orient themselves as far apart as possible.

Trigonal Planar Geometry

In the case of BH3, the VSEPR theory predicts a trigonal planar geometry around the central Boron atom. The three Hydrogen atoms are positioned at 120 degrees from each other in the same plane.

AXN Method and VSEPR Chart

The AXN method is used to determine the geometry of a molecule based on the number of atoms connected to the central atom. A is the central atom, X is the number of outer atoms, and N is the number of lone pairs of electrons.

In the case of BH3, A = Boron, X = 3, and N = 0. The VSEPR chart is a tool used to predict the geometry of a molecule based on the AXN method.

The chart shows the possible geometries based on the number of electron groups around the central atom. The geometry of BH3 is predicted to be trigonal planar based on the AXN method.

Steric Number and Hybridization

The steric number of an atom is the number of atoms and lone pairs of electrons surrounding that atom. In the case of BH3, the steric number of Boron is three, which indicates the trigonal planar geometry.

The hybridization of an atom is a quantum mechanical concept that describes the mixing of atomic orbitals to form hybrid orbitals. In this way, electrons can be shared in covalent bonds.

For BH3, the hybridization of Boron is sp2. This means that Boron forms three sigma bonds with Hydrogen atoms using three sp2 hybrid orbitals.

Bond Angle

The bond angle is the angle between two adjacent bonds in a molecule. For BH3, the bond angle is 120 degrees between all three Hydrogen atoms.


In summary, BH3 has a trigonal planar geometry and is structured with one central Boron atom and three connected Hydrogen atoms. The Lewis structure shows an arrangement that enables each atom to have an octet of electrons, and formal charge calculations show that all atoms in the molecule are neutral.

The VSEPR theory, AXN method, and steric number are useful tools to predict the geometry and arrangement of atoms. The bond angle and hybridization determine the angles and shapes of the orbitals, which affect the nature of the chemical bonds in BH3.

Polar or Nonpolar Nature of BH3

The polarity of a molecule is determined by the symmetry and charge distribution around its atoms. A molecule is polar if its electron charge is unevenly distributed, causing partial positive and negative charges on individual atoms.

A molecule is nonpolar if its charge distribution is evenly distributed such that the molecule has no separate negative or positive charges. Based on this definition, BH3 is a nonpolar molecule.

Symmetry and Charge Distribution

In BH3, Boron has an incomplete octet of electrons, and each Hydrogen atom has a complete outer shell. Unlike other boron compounds, BH3 has a trigonal planar structure, with equal bond angles and symmetrical placement of Hydrogen atoms around the central Boron atom.

Due to the symmetrical arrangement of atoms, the partial charges of the Hydrogen atoms cancel each other out, leading to a nonpolar molecule. Polar molecules typically have partial negative and positive charges on opposing ends of their molecular structures.

This occurs when the electronegativity of the atoms is imbalanced, leading to higher electron density around the more electronegative element and partial charges. As mentioned earlier, BH3 has a symmetrical structure that balances its electron density evenly, making it a nonpolar molecule.

Properties of Borane

Borane is a colorless gas with a strong odor and high reactivity. It is highly toxic and flammable, requiring careful handling.

Because of the incomplete octet in the central Boron atom, borane is prone to undergo various reactions to attain a stable electron configuration. Borane is commonly used as a reducing agent in organic synthesis and as a starting compound for the synthesis of other boron compounds.

It also has applications in the semiconductor industry, hydrogen storage, and rocket fuel. The physical properties of borane include low melting and boiling points, as well as low density.

Borane is only slightly soluble in water, but it can dissolve in organic solvents such as ether, benzene, and acetone.

Reactions of Borane

Borane is highly reactive and can undergo various reactions, depending on the reaction conditions and the presence of other compounds. The following are some of the common reactions of borane:



Hydroboration is a reaction between borane and an alkene or alkyne. The reaction proceeds via an electrophilic addition mechanism where the boron atom of BH3 adds to the double bond of the alkene or alkyne.

The resulting intermediate compound is then converted into an alcohol or alkane. The hydroboration process is an essential method for introducing boron-containing functional groups in organic synthesis.

2. Oxidation

Borane can undergo oxidation by various oxidizing agents such as hydrogen peroxide, oxygen gas, or m-chloroperbenzoic acid.

The reaction results in the formation of boric acid or boron trioxide. The oxidation reaction also produces hydrogen gas, making borane useful in fuel cell technology.

3. Complex Formation

Borane can form complex compounds by reacting with other Lewis bases such as ammonia, phosphine, or alkynes.

The formation of these complexes stabilizes borane’s reactivity and alters its physical and chemical properties. For example, the reaction between borane and ammonia results in the formation of ammonia borane, which is a promising candidate in hydrogen storage for fuel cells.

4. The Reaction as a Reducing Agent

Borane is a powerful reducing agent, and it can reduce a wide range of functional groups, including carbonyl compounds to alcohols, nitro compounds to amines, and halogens to hydrogen.

The reaction of borane with a carbonyl group, such as an aldehyde or ketone, produces an alcohol. Borane has a broad range of applications in organic chemistry, including its use in the reduction of organic compounds, the hydroboration of alkenes, and the production of boron-containing compounds.

While borane itself is highly reactive, it can be used as a starting material to synthesize other borane compounds with specific chemical and physical properties.

Summary of BH3

BH3, or boron trihydride, is a simple and highly reactive molecular compound consisting of a central Boron atom and three Hydrogen atoms. In the previous sections, we have discussed the valence electrons, molecular geometry, Lewis structure, hybridization, bond angle, polar or nonpolar nature, and formal charge of BH3.

In this section, we summarize and integrate all this information.

Valence Electrons, Molecular Geometry, and Lewis Structure

The central Boron atom in BH3 has three valence electrons, while each Hydrogen atom has one. The molecular geometry is a trigonal planar shape, with the three Hydrogen atoms positioned 120 degrees apart in the same plane.

In the Lewis structure of BH3, each Hydrogen atom is bonded to the central Boron atom through a single covalent bond. In addition, the Boron atom forms an incomplete octet of six valence electrons and has no lone pairs of electrons.

Hybridization and

Bond Angle

The bonding in BH3 can be explained by hybridization theory, where the atomic orbitals of the Boron atom combine to give three hybrid orbitals with sp2 hybridization. The hybrid orbitals overlap with the orbitals of the three Hydrogen atoms, forming three sigma bonds.

The bond angle between the Hydrogen-Boron-Hydrogen (H-B-H) atoms is 120 degrees because of the trigonal planar arrangement of the atoms. In other words, the angle between any two Hydrogen atoms attached to Boron is 120 degrees.

Polar or Nonpolar Nature

The polar or nonpolar nature of BH3 is based on the distribution of charges between atoms. A molecule is considered polar if there is an uneven distribution of electrons between atoms, resulting in a partial negative charge on one end and a partial positive charge on the opposite end.

In BH3, the symmetrical arrangement of three Hydrogen atoms around a central Boron atom results in the same partial positive charge on all three Hydrogen atoms. The resulting charge distribution is evenly distributed, and there are no separate partial positive and negative charges.

As a result, BH3 is a nonpolar molecule.

Overall Formal Charge

The overall formal charge of a molecule is the sum of the formal charges of all the atoms in the molecule. The formal charge of an atom refers to the net charge on an atom in a molecule.

In BH3, each Hydrogen atom has a formal charge of zero since it has one valence electron and one bond. The Boron atom has three valence electrons and three bonds, which give it a formal charge of zero as well.

Overall, there are no charges on the atoms and the total formal charge of the molecule is zero.


This article has covered various aspects of BH3, from its valence electrons, molecular geometry, Lewis structure, hybridization, bond angle, polar or nonpolar nature, and formal charge. BH3’s unique structure and properties make it a useful precursor to other boron trihydride compounds.

An understanding of BH3 helps in the prediction of its chemical reactivity and application in various fields such as organic synthesis, hydrogen storage, and fuel cell technology. In conclusion, BH3 is a key molecule in the field of boron chemistry, and its study has broad applications in fundamental research and practical applications in the industry.

In conclusion, BH3 is a nonpolar molecule with a trigonal planar geometry. Its valence electrons and Lewis structure allow for a complete octet of electrons.

The hybridization of the central Boron atom is sp2, resulting in a bond angle of 120 degrees. BH3’s reactivity and applications make it a significant compound in fields such as organic synthesis and fuel cell technology.

Overall, understanding BH3’s structure and properties provides insights into its unique behavior and potential uses in various scientific and industrial contexts. FAQs:


Is BH3 a polar or nonpolar molecule? BH3 is a nonpolar molecule due to its symmetrical structure and even charge distribution.

2. What is the molecular geometry of BH3?

The molecular geometry of BH3 is trigonal planar, with the three Hydrogen atoms positioned 120 degrees apart. 3.

How many valence electrons does BH3 have? BH3 has a total of six valence electrons, with Boron contributing three and each Hydrogen atom contributing one.

4. What is the hybridization of the central Boron atom in BH3?

The central Boron atom in BH3 undergoes sp2 hybridization, forming three hybrid orbitals. 5.

What is the bond angle in BH3? The bond angle in BH3 is 120 degrees, as determined by the trigonal planar geometry.

6. What are the applications of BH3?

BH3 is commonly used as a reducing agent in organic synthesis and as a starting compound for the synthesis of other boron compounds. It also has applications in the semiconductor industry, hydrogen storage, and rocket fuel.

7. Is BH3 a stable compound?

BH3 is highly reactive and unstable on its own. However, it serves as a starting point for the synthesis of more stable boron compounds with specific properties and applications.

8. Can BH3 form hydrogen bonds?

No, BH3 cannot form hydrogen bonds because there are no hydrogen atoms bonded to a highly electronegative atom like oxygen, nitrogen, or fluorine. Hydrogen bonding requires a hydrogen atom bonded to an electronegative atom and a lone pair on another electronegative atom.

9. Is BH3 toxic?

Yes, BH3 is highly toxic and flammable and requires careful handling. It is essential to follow proper safety protocols when working with this compound.

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