Question

Describe the bonding in linear, covalent \(\mathrm{BeCl}_{2}\) and planar, covalent \(\mathrm{BCI}_{3}\). What is the difference in the hybrid orbitals used?

Short answer

The bonding in linear, covalent \(\mathrm{BeCl}_{2}\) involves the central Be atom forming two sigma bonds with two Cl atoms using sp hybrid orbitals, which are formed by the combination of one s and one p orbital. The geometry is linear with bond angles of 180°. In planar, covalent \(\mathrm{BCl}_{3}\), the central B atom forms three sigma bonds with three Cl atoms using sp² hybrid orbitals, created by combining one s and two p orbitals. The geometry is trigonal planar with bond angles of 120°. The difference in hybrid orbitals lies in the mixing of orbitals and resulting geometry: \(\mathrm{BeCl}_{2}\) is linear and uses sp hybrid orbitals, while \(\mathrm{BCl}_{3}\) is planar and uses sp² hybrid orbitals.

Step-by-step solution

Determine the central atom and the number of valence electrons

For both molecules, we first need to identify the central atom that forms the bonds with other atoms. In \(\mathrm{BeCl}_{2}\), Beryllium (Be) is the central atom. It has 2 valence electrons. In \(\mathrm{BCl}_{3}\), Boron (B) is the central atom. It has 3 valence electrons.

Determine the hybridization for each molecule

Next, we identify the hybridization of the central atom of each molecule. In \(\mathrm{BeCl}_{2}\), Be forms two sigma bonds with two Cl atoms. As it forms 2 bonds, the hybridization for Be is sp. In \(\mathrm{BCl}_{3}\), B forms three sigma bonds with three Cl atoms. As it forms 3 bonds, the hybridization for B is sp².

Describe the bonding in each molecule

For \(\mathrm{BeCl}_{2}\), the hybridization of Be is sp. One of the s orbitals and one of the p orbitals combine to form two sp hybrid orbitals. These sp hybrid orbitals are linearly arranged around the central Be atom at 180° angles. Be forms sigma bonds with Cl atoms using these hybrid orbitals. For \(\mathrm{BCl}_{3}\), the hybridization of B is sp². One s orbital and two p orbitals combine to form three sp² hybrid orbitals. These sp² hybrid orbitals are arranged in a trigonal planar shape around the central B atom, with bond angles of 120°. B forms sigma bonds with Cl atoms using these hybrid orbitals.

Compare the differences in hybrid orbitals

In summary, the difference between the hybridization of \(\mathrm{BeCl}_{2}\) and \(\mathrm{BCl}_{3}\) lies in the way the orbitals mix and the geometry of the resulting molecules. \(\mathrm{BeCl}_{2}\) is linear and utilizes sp hybrid orbitals, formed by mixing of one s and one p orbital. On the other hand, \(\mathrm{BCl}_{3}\) is planar and utilizes sp² hybrid orbitals, formed by mixing one s and two p orbitals.

Key concepts

Covalent Bonding

Covalent bonding is the process where two atoms share pairs of electrons to achieve a full outer electron shell, leading to a more stable molecule. Covalent bonds can be single, double, or triple, based on how many pairs of electrons are shared.

• Single covalent bonds involve the sharing of one pair of electrons between atoms.
• Double covalent bonds involve two pairs of shared electrons.
• Triple covalent bonds occur with the sharing of three pairs of electrons.

These bonds usually occur between nonmetal atoms, allowing them to complete their valence shells. In the case of beryllium chloride (\(\text{BeCl}_{2}\)) and boron trichloride (\(\text{BCl}_{3}\)), the covalent bonds are crucial for their stability, involving the sharing of electrons between beryllium or boron and chlorine atoms. These compounds exhibit different geometries due to their unique covalent interactions and hybridization types.

sp Hybridization

The concept of sp hybridization is essential in predicting the geometry of certain molecules like \(\text{BeCl}_{2}\). During sp hybridization, one s orbital and one p orbital from the same atom mix to form two equivalent sp hybrid orbitals. These orbitals are oriented linearly at a bond angle of 180°, leading to a straight-line configuration of the molecule. This geometry is crucial in determining how beryllium forms bonds with chlorine atoms in \(\text{BeCl}_{2}\). The linearly aligned sp hybrid orbitals in beryllium allow it to form strong, direct sigma bonds with each chlorine atom, resulting in a stable structure. Understanding sp hybridization helps explain why some molecules prefer linear arrangements and how electron pair sharing occurs in such configurations.

sp² Hybridization

sp² hybridization occurs when one s orbital and two p orbitals mix to give three equivalent sp² hybrid orbitals. These charge clouds are arranged trigonal-planar around the central atom, with bond angles set at 120°. This type of hybridization is beautifully illustrated in boron trichloride (\(\text{BCl}_{3}\)). In \(\text{BCl}_{3}\), the boron atom undergoes sp² hybridization, which results in three planar sp² orbitals pointing towards the corners of an equilateral triangle. This configuration allows for the formation of strong sigma bonds with three chlorine atoms, creating a stable planar structure. The choice of sp² hybridization in molecules like \(\text{BCl}_{3}\) showcases the versatility of hybrid orbitals and how their arrangement impacts molecular geometry and bonding.

BeCl₂

BeCl₂ is composed of beryllium, a central atom, bonded linearly to two chlorine atoms with covalent bonds. Such an arrangement is significant due to its sp hybridization. In this molecule, \(\text{Be}\) pools one of its s-orbitals with a p-orbital to create two sp hybrid orbitals. Beryllium, having only two valence electrons, forms a sigma bond with each chlorine atom through these sp orbitals.The linear geometry of \(\text{BeCl}_{2}\), often visualized as angles of 180° between the bonds, is attributed to the sp hybridization.This linear arrangement is why \(\text{BeCl}_{2}\) is often utilized as a model for understanding linear covalent structures.

BCl₃

BCl₃, or boron trichloride, is another fascinating example of molecular hybridization, specifically showcasing sp² hybridization. Boron, as the central atom, mixes its s-orbital with two p-orbitals to produce three sp² hybrid orbitals. These orbitals shape the molecule into a trigonal-planar formation, allowing boron to bind effectively with three chlorine atoms. The 120° angle between these bonds is a classic feature of sp² hybridization, leading to a stable and even distribution of electron pairs around the boron atom. The molecular geometry of \(\text{BCl}_{3}\) not only showcases symmetry but maximizes spatial separation, minimizing electron pair repulsion. Understanding BCl₃ helps crystalize how hybrid orbitals determine both the shape and the stability of covalent compounds.