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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 51b

Indicate the hybridization of the central atom in b. AlCl4

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Determine the central atom in the molecule. In AlCl_4^-, the central atom is aluminum (Al).
Count the total number of valence electrons for the central atom. Aluminum (Al) has 3 valence electrons.
Consider the charge of the ion. AlCl_4^- has a -1 charge, so add 1 more electron to the total count for the central atom.
Count the number of atoms bonded to the central atom. There are 4 chlorine (Cl) atoms bonded to aluminum (Al).
Use the steric number to determine hybridization. The steric number is the sum of bonded atoms and lone pairs on the central atom. For AlCl_4^-, the steric number is 4, indicating sp^3 hybridization.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hybridization

Hybridization is a concept in chemistry that describes the mixing of atomic orbitals to form new hybrid orbitals. These hybrid orbitals are used to explain the geometry and bonding properties of molecules. The type of hybridization depends on the number of electron pairs around the central atom, which influences the molecular shape.
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Valence Shell Electron Pair Repulsion (VSEPR) Theory

VSEPR theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to this theory, electron pairs will arrange themselves as far apart as possible to minimize repulsion, which helps determine the molecular shape and hybridization of the central atom.
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Aluminum Chloride (AlCl4–) Structure

In the case of AlCl4–, aluminum is the central atom surrounded by four chloride ions. The presence of a negative charge indicates an additional electron, which affects the hybridization. The geometry of AlCl4– is tetrahedral, leading to the conclusion that the hybridization of aluminum in this complex is sp3, as it forms four equivalent bonds with the chloride ions.
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