Problem 14 - Chemistry Principles and Practice

Question

Identify the hybrid orbitals used by antimony in \(\mathrm{SbCl}_{5}\) and in \(\mathrm{SbCl}_{6}^{-},\) the ion formed from the reaction of \(\mathrm{SbCl}_{5}\) and \(\mathrm{Cl}^{-}\). Explain your choices.

Step-by-Step Solution

Answer

In \( \mathrm{SbCl}_{5} \), antimony uses sp3d hybridization; in \( \mathrm{SbCl}_{6}^{-} \), it uses sp3d2 hybridization.

Step 1: Analyze SbCl5 Hybridization

The molecule \( \mathrm{SbCl}_{5} \) has a trigonal bipyramidal geometry. This means that antimony uses 5 sp3d hybrid orbitals. These arise from the mixing of one s orbital, three p orbitals, and one d orbital to accommodate the five bonds with chlorine atoms.

Step 2: Analyze SbCl6- Ion Hybridization

In \( \mathrm{SbCl}_{6}^{-} \), the anion forms when an additional Cl- ion bonds with \( \mathrm{SbCl}_{5} \). The geometry becomes octahedral. Antimony uses 6 sp3d2 hybrid orbitals to accommodate the six bonds with chlorine atoms. These come from one s, three p, and two d orbitals.

Key Concepts

Trigonal bipyramidal geometry

Trigonal bipyramidal geometry describes a molecular shape that can be visualized as a three-legged stool with a top and bottom. This geometry is common in molecules where a central atom, like antimony in \( \mathrm{SbCl}_5 \), is surrounded by five other atoms. In this configuration, two of the positions are axially aligned—directly opposite each other—while the remaining three atoms sit in equatorial positions around the central atom.

This geometry is crucial because it influences how the molecule interacts with other molecules, impacting its physical and chemical properties. The bond angles in a trigonal bipyramidal geometry are typically 90° between axial and equatorial atoms, and 120° between equatorial atoms themselves, balancing repulsions across the molecule.

• Axial positions: Vertically aligned from the central atom.
• Equatorial positions: Around the central atom in a plane.

Understanding this geometry helps predict molecular behavior and reactivity.

Octahedral geometry

Octahedral geometry describes a molecular shape where six atoms or groups of atoms are symmetrically arranged around a central atom. Picture it like an eight-faced die. In the case of \( \mathrm{SbCl}_6^- \), when chloride ion bonds with \( \mathrm{SbCl}_5 \), the structure becomes octahedral.

This geometry is particularly stable and symmetric, characterized by having all bond angles at 90°. This allows for an equal distribution of bond energies, which affects coordination and stability of the molecule.

• All bond angles equal at 90°.
• Perfect symmetry aids in stabilizing compound.

In chemical complexes, this geometry is commonly found in coordination compounds and influences how these complexes interact in solutions and with other molecules.

sp3d hybrid orbitals

The concept of sp3d hybrid orbitals emerges when a central atom needs to use five orbitals to form bonds, such as in \( \mathrm{SbCl}_{5} \). The hybridization involves mixing one s orbital, three p orbitals, and one d orbital from the antimony atom. This blending results in five equivalent hybrid orbitals.

These orbitals are oriented in a way that facilitates the formation of the trigonal bipyramidal shape, allowing the molecule to achieve the most stable configuration possible. Hybrid orbitals are a key concept allowing atoms to form more complex structures than pure s and p orbital combinations can.

• Combines s, three p, and one d orbital.
• Yields five orbitals enabling specific geometric structure.

By understanding this, one can predict bonding patterns and molecular shapes in compounds.

sp3d2 hybrid orbitals

sp3d2 hybrid orbitals come into play when a molecule like \( \mathrm{SbCl}_{6}^- \) requires six orbitals to form its bonds, resulting in an octahedral geometry. These are formed by combining one s orbital, three p orbitals, and two d orbitals from the central atom.

This type of hybridization allows for more complex shapes and bonding, accommodating the extra electron pairs present in complex ions or molecules with expanded octets than what is possible with just s and p orbitals.

• Uses one s, three p, and two d orbitals.
• Provides necessary configuration for six bonding pairs.

With sp3d2 hybridization, molecules can achieve a sophisticated level of symmetry and stability, crucial for understanding complex inorganic compounds and coordination chemistry.