Lewis Structure of BeCl2, Molecular Geometry of BeCl2, Hybridization, Polarity, and MO Diagram

Beryllium chloride, abbreviated as BeCl2, is an inorganic chemical. At room temperature, it appears as a white or yellow crystal solid. It can take the shape of a monomer or a 1-D polymer. Because of the diagonal relationship between beryllium and aluminium, the characteristics of beryllium chloride are comparable to those of aluminium chloride.

Beryllium chloride has a molar mass of 79.91 g/mol and a melting point of 399 °C, respectively. The chemical bonding in Beryllium Chloride is investigated using the Lewis technique, which involves writing down its Lewis structure.

Following the Lewis structure, it is necessary to comprehend the molecular geometry and hybridization of the core atom, Beryllium. To comprehend the MO diagram of beryllium chloride, the molecular orbital (MO) theory will be applied.

Lewis Structure of BeCl2

The electrons in an atom’s outermost shell are displayed in any molecule’s Lewis structure. There will be both bonding and non-bonding electrons in these electrons.

Beryllium has the electronic configuration [He] 2s2 and chlorine has the electronic configuration [Ne] 3s23p5. Be and Cl have two electrons on their valence shells and seven electrons on their valence shells, respectively. Because beryllium chloride contains two chlorine atoms, the total number of valence electrons is 2 + (7 X 2) =16.

Because the valence electrons in the Lewis structure of the molecule are depicted as dots, it is also known as electron dot structure or Lewis dot structure.

It’s a two-dimensional structure in which each atom in the molecule tries to finish its octet by sharing, acquiring, or losing electrons.

There are, however, a few exceptions. Hydrogen, Helium, Lithium, and Beryllium, for example, are unable to complete their octet and thus prefer to have duplets (two electrons).

We now have 16 valence electrons to arrange in the Lewis structure of BeCl2, and we must do so. As previously stated, the beryllium will be surrounded by two electrons.

To complete its octet, the chlorine atom would prefer to have eight electrons surrounding it. Beryllium will be the centre atom, surrounded by chlorine atoms.

As a result, the Lewis structure of beryllium chloride could be as follows:

Lewis structure of BeCl2

It can also be represented in bond form as a single bond formed by two shared electrons. As a result, the Lewis structure of beryllium chloride is as follows:

Lewis structure of BeCl2

Both representations are accurate, therefore they can be represented in any of the two ways. By sharing one electron with the beryllium atom, each chlorine atom completes its octet. As a result, the Beryllium and Chlorine atoms share a single bond.

Beryllium chloride is electron-deficient and works as Lewis acid because the octet of beryllium is incomplete.

What might BeCl2’s molecular form be now?

Based on the Lewis structure, we can’t tell anything. In order to anticipate the structure of beryllium chloride, we must examine the Valence shell electron pair repulsion (VSEPR) hypothesis.

Let’s have a look at the VSEPR theory.

Molecular Geometry of BeCl2

Bond pair – Bond pair, Bond pair – Lone pair, and Lone pair – Lone pair repulsions are used in VSEPR theory to calculate the molecule’s molecular structure. It also just includes valence shell electrons, which can be bound or not.

Beryllium is a central atom in the Lewis structure of Beryllium chloride, with only two bond pairs. The following table can simply anticipate its shape. Beryllium’s general formula is AX2, since it forms two bond pairs with two chlorine atoms.

General formulaNumber of bond pairsMolecular shape/geometry
AX1Linear
AX22Linear
AX33Trigonal planar
AX44Tetrahedral
AX55Trigonal bipyramidal
AX66Octahedral

As a result, Beryllium Chloride will have a linear form, or a linear molecular geometry.

Beryllium Chloride’s linear geometry results in a bond angle (Cl-Be-Cl) of 180°, which minimises bond pair-bond pair repulsions. Bond pair-bond pair repulsion will not be minimal if the bond angle is higher than or less than 180°.

Let us now look at the valence bond theory (VBT) to learn about Beryllium’s hybridization in Beryllium Chloride.

Geometry of BeCl2

Hybridization of BeCl2

The atomic orbitals of the core atom fuse together to generate hybrid orbitals of equivalent energy, according to valence bond theory (VBT).

Bond formation occurs when these hybrid orbitals collide with the atomic orbitals of nearby atoms.

Beryllium’s electrical configuration in its ground state is [He] 2s2.

Because there is only one pair of electrons in the 2s orbital, there is only one pair of electrons. According to VBT, coupled orbitals cannot participate in bond formation. As a result, one of the electrons from the 2s orbital will excite to Beryllium’s 2p orbital.

Promotion energy is the amount of energy necessary for the excitation of an electron, and it is derived from the establishment of a link between Beryllium and Chlorine atoms.

Beryllium’s excited-state electrical configuration is now [He] 2s12p1.

Beryllium atom’s two 2s and two 2p orbitals will combine to generate two sp hybrid orbitals with the same energy. Beryllium’s sp hybrid orbitals will overlap with the 3p orbitals of chlorine atoms, resulting in the development of a sigma bond between Beryllium and chlorine.

Its orbital diagram can be used to show the same thing. Beryllium chloride’s orbital diagram would be:

As a result, the Beryllium atom hybridization in Beryllium chloride is sp. A steric number can also be used to compute it.

Number of atoms linked to the centre atom + Number of lone pairs of electrons at the central atom = Steric number

There are now two atoms bound to the Beryllium atom, and the Beryllium atom has no single pair of electrons.

As a result, the steric number is 2 and the hybridization is sp.

Hybridization of BeCl2

Polarity of BeCl2

The chemical BeCl2 is classified as a nonpolar molecule.

Because the molecule’s form is symmetric, or linear, the net dipole of the entire molecule becomes zero, leaving no partial charge.

Both Chlorine atoms have the same electronegativity, hence they have equal influence on the shared electrons.

Check out the polarity of BeCl2 for further details.

MO diagram for BeCl2.

Mulliken and Hund’s Molecular Orbital Theory discusses the chemical bonding of the molecule in further detail. It generates a molecular orbital or energy level diagram based on the linear combination of atomic orbitals.

According to this idea, molecular orbitals are formed by combining atomic orbitals with identical energy and symmetry around the molecule axis. The number of molecular orbitals will be equal to the number of atomic orbitals that combine.

Two atomic orbitals, for example, combine to generate two molecular orbitals, one of which is bonding and the other antibonding.

Antibonding molecule orbitals are greater in energy than individual atomic orbitals and hence less stable. Bonding molecular orbitals are lower in energy and thus more stable than individual atomic orbitals.

Beryllium atomic orbitals and chlorine group orbitals are used to build the molecular orbital diagram of the BeCl2 molecule.

Because there are two chlorine atoms, they combine to form group orbitals first.

Cl has the electronic configuration [Ne] 3s23p5. One chlorine atom’s 3s atomic orbital will now merge with the 3s atomic orbitals of other chlorine atoms to form two 3s group orbitals with the same energy.

Similarly, three 3p orbitals of one chlorine atom join with three 3p orbitals of other chlorine atoms to produce six comparable 3p group orbitals.

The symmetry of the two 3s and six 3p group orbitals is as follows. The linear combination of atomic orbitals can likewise be used to get these results.

Bonding group orbitals were given the numbers 3s, 3px, 3py, and 3pz (left hand side), while antibonding group orbitals were given the numbers 3s, 3px, 3py, and 3pz (right hand side).

Because chlorine is more electronegative than beryllium, its energy is lower than that of beryllium. The molecular orbital diagram of BeCl2 will be drawn by integrating atomic orbitals of beryllium atoms with identical energy and symmetry with group orbitals of chlorine atoms around a molecular axis.

Because the energy of the 3s group orbitals of chlorine atom is so low compared to the 2s and 2p atomic orbitals of beryllium atom, they will stay non-bonding.

Similarly, 3px* and 3py* group orbitals are non-bonding because their symmetry does not match the beryllium atom’s 2s and 2p atomic orbitals.

The beryllium atom’s 2s atomic orbital will now join with a chlorine atom’s 3pz* group orbital to form bonding and antibonding molecular orbitals. The symmetry of these two orbitals is comparable, and their energies are likewise close.

Similarly, the beryllium atom’s 2pz atomic orbital will join with the chlorine atom’s 3pz group orbital to produce bonding and antibonding molecular orbitals.

The beryllium atom’s 2px and 2py atomic orbitals join with a chlorine atom’s 3px and 3py group orbital to form two bonding and two antibonding molecular orbitals.

As a result, beryllium chloride’s molecular orbital diagram would be:

Diagram of the BeCl2 MO

The Aufbau principle, which follows Pauli’s exclusion principle and Hund’s rule, fills the sixteen valence electrons in molecular orbitals.

Conclusion

Beryllium chloride is an inorganic chemical that dissolves in a wide range of polar solvents. It acts as a catalyst in the Friedel-Craft reaction because it is a Lewis acid.

Every facet of chemical bonding in beryllium chloride has been investigated in this paper. We started with the Lewis structure, which is a two-dimensional depiction of the structure. Beryllium chloride has a linear molecular structure and exhibits sp hybridization.

Beryllium chloride’s molecular orbital diagram is also investigated. It is based on the linear combination of the beryllium atom’s atomic orbitals and the chlorine atom’s group orbitals.

In summary, we’ve gone over all of beryllium chloride’s fundamental features.

More suggestions for improvement are always welcome.

Thank you for taking the time to read this.

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Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

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