Question

Indicate the hybridization of the central atom in (a) \(\mathrm{BCl}_{3}\), (b) \(\mathrm{AlCl}_{4}^{-}\), (c) \(\mathrm{CS}_{2}\) (d) \(\mathrm{KrF}_{2}\), (e) \(\mathrm{PF}_{6}^{-}\).

Short answer

The hybridization of the central atoms in the given molecules/ions is as follows: (a) BCl3: sp2 (b) AlCl4−: sp3 (c) CS2: sp (d) KrF2: sp3d (e) PF6−: sp3d2

Step-by-step solution

Determine the number of electron pairs around the central atom

To find the number of electron pairs surrounding the central atom, we will first determine the total number of valence electrons for each of the given molecules or ions. Then, we will decide how these valence electrons are distributed around the central atom, which includes bonding and non-bonding pairs.

Use the number of electron pairs to determine hybridization

Depending on the number of electron pairs around the central atom, we will determine the hybridization as follows: - 2 electron pairs: sp hybridization - 3 electron pairs: sp2 hybridization - 4 electron pairs: sp3 hybridization - 5 electron pairs: sp3d hybridization - 6 electron pairs: sp3d2 hybridization Now, let's find the hybridization for each molecule/ion: (a) BCl3

Determine the number of electron pairs around B

B has 3 valence electrons, and each Cl has 7 valence electrons. In BCl3, B is the central atom, and it forms 3 single bonds with 3 Cl atoms. Therefore, there are 3 bonding electron pairs around the B atom.

Determine the hybridization of B in BCl3

Since there are 3 electron pairs around B, it undergoes sp2 hybridization. (b) AlCl4−

Determine the number of electron pairs around Al

Al has 3 valence electrons, and each Cl has 7 valence electrons. The ion has a total of one extra electron which is added to the total valance electrons, and we get 3 + (7 * 4) + 1 = 32 valence electrons. In AlCl4−, Al is the central atom and forms 4 single bonds with 4 Cl atoms. Therefore, there are 4 bonding electron pairs around the Al atom.

Determine the hybridization of Al in AlCl4−

Since there are 4 electron pairs surrounding the Al atom, it undergoes sp3 hybridization. (c) CS2

Determine the number of electron pairs around C

C has 4 valence electrons, and each S has 6 valence electrons. In CS2, C is the central atom and forms 2 double bonds with 2 S atoms. Therefore, there are 2 bonding electron pairs around the C atom.

Determine the hybridization of C in CS2

Since there are 2 electron pairs surrounding the C atom, it undergoes sp hybridization. (d) KrF2

Determine the number of electron pairs around Kr

Kr has 8 valence electrons and each F has 7 valence electrons. In KrF2, Kr is the central atom and forms 2 single bonds with 2 F atoms. So there are 2 bonding electron pairs and 3 nonbonding electron pairs around Kr.

Determine the hybridization of Kr in KrF2

Since there are 5 electron pairs surrounding the Kr atom, it undergoes sp3d hybridization. (e) PF6−

Determine the number of electron pairs around P

P has 5 valence electrons, and each F has 7 valence electrons. The ion carries one extra electron which is added to the total valance electrons, we get 5 + (7 * 6) + 1 = 48 valence electrons. In PF6−, P is the central atom and forms 6 single bonds with 6 F atoms. Therefore, there are 6 bonding electron pairs around the P atom.

Determine the hybridization of P in PF6−

Since there are 6 electron pairs surrounding the P atom, it undergoes sp3d2 hybridization. In summary, the hybridization of the central atoms in the given molecules/ions is as follows: (a) BCl3: sp2 (b) AlCl4−: sp3 (c) CS2: sp (d) KrF2: sp3d (e) PF6−: sp3d2

Key concepts

Valence Electrons

Understanding the concept of valence electrons is paramount when discussing chemical hybridization. Valence electrons are the electrons present in the outermost shell of an atom. These electrons are significant because they take part in chemical bonding, determining how atoms combine and interact with each other.

Every element has a characteristic number of valence electrons that defines its chemical properties. For example, carbon has four valence electrons, which allows it to form up to four bonds with other atoms. In the exercise, determining the number of valence electrons in the central atom of each compound is the first step in predicting the electron pair geometry and hybridization. For instance, in BCl3, boron has three valence electrons and in CS2, carbon has four. This key information guides us to their bonding capabilities and helps us understand why BCl3 has sp2 hybridization and CS2 has sp hybridization.

• Counting valence electrons is the foundational step in hybridization determination.
• Valence electrons allow atoms to participate in chemical bonding.
• Knowing the number of valence electrons helps predict the molecule's structure.

Electron Pair Geometry

Electron pair geometry is the three-dimensional arrangement of electron pairs around a central atom in a molecule. This includes both bonding pairs, which are shared with other atoms to form chemical bonds, and non-bonding pairs, also known as lone pairs, that are not shared and remain on the central atom.

The geometry is determined by the number of electron pairs around the central atom, which repel each other and adopt a configuration that minimizes repulsion. These geometries can be linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral.

In the given exercise, the electron pair geometry influences molecular hybridization. For example, in BCl3 with its three bonding pairs and no lone pairs, the electron pair geometry is trigonal planar. In contrast, KrF2 has two bonding pairs and three lone pairs, leading to a trigonal bipyramidal electron pair geometry, which is crucial in identifying its sp3d hybridization.

• Geometry is based on the repulsion between electron pairs.
• The shape of a molecule is determined by its electron pair geometry.
• Electron pair geometry helps to explain the molecule's hybridization.

Molecular Hybridization

Molecular hybridization is a concept that explains the mixing of atomic orbitals to form new hybrid orbitals that are suitable for the pairing of electrons to form chemical bonds. It's an integral part of understanding molecular geometry and bonding.

The type of hybridization depends on the number of electron pairs around the central atom. For instance, sp hybridization occurs when one s orbital and one p orbital mix to accommodate two electron pairs. Moving up, sp2, sp3, sp3d, and sp3d2 hybridizations involve the mixing of a greater number of orbitals to accommodate more electron pairs.

In the context of the exercise, a molecule like BCl3, which has three bonding pairs, will have an sp2 hybridization state. This state involves the mixing of one s orbital and two p orbitals. Following the same logic, PF6− with six bonding electron pairs has an sp3d2 hybridization, combining one s, three p, and two d orbitals.

• Hybridization explains how orbitals mix to form bonds.
• It is determined by the electron pair count around the central atom.
• Different hybridizations correspond to different molecular geometries.