BH3 Lewis Structure, Characteristics: 13 Must To Know Facts

BH3 is the chemical formula of Boron tri- hydride. It is also known as Boranes.

BH3 (borane) is comes under natural products which is originated from Erysimum inconspicuum. IUPAC name for BH3 is borane which is also known as trihydrido borane. BH3 consists of one boron atom and three hydrogen atoms. Molecular weight of Boron tri- hydride is 13.84. Here, in this editorial we are learning about BH3 lewis structure.

How to draw BH3 lewis structure?

To draw the lewis structure there are some rules to be followed like count total valence electrons, select the central metal atom which have lowest electronegativity, octet rule, formal charge, etc. In BH3 lewis structure, the boron atom belongs to 3rd group of periodic table and hydrogen atom belongs to 1st group of periodic table having 3 and 2 valence electrons respectively.

The Boron atom has electronegativity 2.04 and the hydrogen atom has electronegativity 2.2. So, boron atom has lowest electronegativity than hydrogen atom. Thus boron atom should be situated in the central position of the BH3 lewis structure. Then we have to make bonds between H and three H atoms to connect them with each other.

The BH3 lewis structure has three boron hydrogen (B-H) bonds. So, it has three bond pairs and zero lone electron pairs in BH3 leis structure. As the Born atom gains the central position due to lowest electronegativity, thus all the three hydrogen atom gets linked to boron atom.

bh3 lewis structure
BH3 lewis structure

BH3 valence electrons

To determine valence shell of BH3 lewis structure, check the group positions of B and H atoms in periodic table. The boron atom belongs to 3rd group of periodic table and having three valence electrons in its outer shell orbital. Similarly hydrogen atom belongs to 1st group of periodic table and thus having one valence electron in its outer shell orbital.

Boron total valence electrons = 03

Hydrogen total valence electrons = 01

BH3 lewis structure valence electrons = 03 (B) + 1 x 3 (H) = 3 + 3 = 6

Hence, BH3 lewis structure has total six valence electrons.

If we are doing bonding between boron and hydrogen atom we need the valence electrons for bonding. Thus, three valence electrons of boron atom and one valence electron of three hydrogen atoms, total six electrons get consumed in B-H bondings. So, we don’t have any more valence electrons for further sharing in BH3 lewis structure.

Valence electrons in BH3 lewis structure

BH3 lewis structure octet rule

Octet rule tells us about the presence of complete eight electrons in its valence shell last orbital. Boron atom contains three valence electron as it is comes under 2nd group of periodic table and hydrogen atom contains one valence electrons as it comes under the 1st group of periodic table.

Both boron and hydrogen atoms share their valence electrons with each other to form three boron hydrogen (B-H) bonds. So, all the valence electrons of BH3 lewis structure get engaged in bonding remaining no electrons for further sharing.

Thus, boron atom contains six electrons after bonding, two electrons present in each B-H bonds. So, boron atom has incomplete octet. Similarly all three hydrogen atoms contain two electrons (bond pair electrons). Thus three hydrogen atoms also has incomplete octet. As both H and B atoms do not contain eight electrons, so they both have incomplete octet.

BH3 lewis structure formal charge

Formal charge calculation of any lewis structure is done by the following formula:

Formal charge = (valence electrons – non-bonding electrons – ½ bonding electrons)

Let us calculate the formal charge for BH3 lewis structure.

Boron atom: Boron atoms Valence electrons = 03

                     Boron atoms Lone pair electrons = 00

                     Boron atoms Bonding electrons = 06 (three single bond)

Formal charge on boron atom = (3 – 0 – 6/2) = 0

So, the boron atom has zero formal charge in BH3 lewis structure.

Hydrogen atom: Hydrogen atom have Valence electrons = 01

                          Hydrogen atom have Lone pair electrons = 00

                          Hydrogen atom have Bonding electrons = 2 (one single bond)

Formal charge on iodine = (1 – 0 – 2/2) = 0

So, all the three hydrogen atoms in BH3 molecule have zero formal charges.

BH3 lewis structure lone pairs

The BH3 lewis structure has total six valence electrons in its BH3 molecule. As boron atom has three valence electrons and hydrogen atom has one valence electron, which they get shared with each other for bonding between them i.e. forming three B-H bonds. Hence all the six valence electrons get used for bonding and no more valence electrons are remain for further sharing.

As one single B-H bond contains two electrons, thus 3 (bonds) x 2 (electrons) = 6. OR 6 (valence electrons) / 2 (electrons) = 3 bonds (B-H). Therefore, 6 (valence electrons) – 6 (bonding electrons) = 0. Hence, there are no lone pair electrons are present in B and H atoms in BH3 lewis structure.

BH3 lewis structure shape

BH3 lewis structure contains total three (B-H) covalent bonds forming within central boron atom and outer three hydrogen atoms. No lone electron pairs are present on central B atom and outer three H atoms of BH3 lewis structure. As the three H atoms joined with central boron atom, the BH3 lewis structure has trigonal planar geometry.

Even the shape and molecular geometry of BH3 lewis structure can be determine by VSEPR theory. According to VSEPR theory the AX3 generic formula is applicable on BH3 molecule. ‘A’ is denoted central atom i.e. Boron atom. ‘X’ is denoted number of bonding atoms attached to central atom i.e. three H atoms. Thus as per the VSEPR theory, any molecule follows a generic formula AX3, then it has a electron geometry and molecular geometry trigonal planar.

BH3 hybridization

Hybridization of any lewis structure or molecule is depends upon the calculation of its steric number. The formula for steric number is as follows:

Steric number = sum of number of central atoms connected bonded atoms and lone electron pair present on central atom

Steric number for BH3 = 3 (H atoms) + 0 (lone pair electrons) = 3

As the BH3 lewis structure has 3 calculated steric number means it has sp2 hybridization. Thus the BH3 lewis structure shows sp2 hybridization.

BH3 lewis structure angle

Bond angle is the angle which is formed within the central atom and any two bonding atoms. To form a bond angle there is a need of at least three elements or atoms in a molecule. As the BH3 lewis structure has trigonal planar geometry or shape, so it has 120 degree bond angle. Hence, in BH3 lewis structure the hydrogen boron hydrogen (H-B-H) bond angle formed of 120 degree.

BH3 lewis structure resonance

The resonance structure of any molecule is only possible when it contains multiple bonds (double or triple bonds) and also there should present some formal charges (+ve or –ve) with lone pair electrons present on that molecule.

In BH3 lewis structure, there are only three boron hydrogen (B-H) covalent bonds are present. All the three hydrogen atoms joined with central born atom with three single covalent bonds. Means multiple bonds are absent in BH3 lewis structure. Also no formal charges i.e. zero formal charge on B and H atoms. Even no lone electron pairs are present. So, BH3 molecule cannot show resonance structure.

BH3 solubility

BH3 (boron tri- hydride) is soluble in:

  • Water ( decomposed completely at 100 degree temperature heating)
  • Water (slightly soluble at 20 degree temperature heating)
  • Concentrated sulphuric acid (H2SO4)
  • Ethanol
  • Benzene
  • Ammonium hydroxide (NH4OH)

Is Bh3 ionic?

No, BH3 is not ionic in nature, it is a covalent molecule. As there are three boron hydrogen (B-H) covalent bonds are present in BH3 lewis structure, so it cannot form any charge or dipole to being ionic in nature. Thus BH3 lewis structure or molecule is covalent in nature.

Why BH3 is not ionic?

There is no formal charge is present on central boron atom and outer three hydrogen atoms and also there is no lone electron pair density on B and H atom. Thus it cannot form any positively charged cation or negative charge anion to make the molecule ionic in nature.

How BH3 is not ionic?

As all the three hydrogen atoms gets connected with central boron atom with single strong B-H covalent bonds i.e. three B-H covalent bonds are present in BH3 molecule. So, there is no chance for the formation of positive or negative ion within the molecule. Hence the BH3 molecule is not ionic rather it is covalent in nature.

Is BH3 acidic or basic?

BH3 lewis structure or molecule is considered as a lewsi acid. So, BH3 shows acidic nature and not basic nature.

Why BH3 is acidic?

The electron pair acceptor compound or molecule is known to be a lewis acid. BH3 is a lewis acid as it has only 6 valence electrons which gets used in bonding with three hydrogen atoms. Thus, BH3 molecule is being electron deficient and also it has empty ‘p’ orbitals to easily accept electrons from other molecules. Thus it is lewis acid.

How BH3 is acidic?

As the BH3 molecule do not have lone electron pairs because all six valence electrons get used in B-H bonding and also it has an incomplete octet. Because of this reasons BH3 molecule can readily accept electrons from any lewis bases which makes BH3 a lewis acid molecule.

Is BH3 polar or nonpolar?

BH3 lewis structure or molecule is non- polar in nature. As there is no polar bonds present in BH3 molecule. To determine the polar or non- polar nature of any molecule we should check two things i.e. presence of at least one covalent  polar bond and symmetry of molecule.

Why BH3 is non- polar?

Boron and hydrogen atoms have almost similar electronegativity i.e. 2.04 and 2.20. So there is not much difference between electronegativities of B and H atom, which makes the BH3 molecule non- polar in nature.

How BH3 is non- polar?

The BH3 molecule has symmetrical structure as all the three boron hydrogen (B-H) bonds have equal bond length, due to which the dipole moment creates in molecule gets cancel each other i.e. net zero dipole moment is present in BH3 molecule. Thus, it is non- polar molecule.

Conclusion:

BH3 consists of one B and three H atoms. BH3 has 6 valence electrons and three B-H covalent bonds. It is a lewis acid and non- polar molecule. Also it has no lone electron pairs and trigonal planar in shape with sp2 hybridization and 120 degree bond angle.