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Difficulty: MediumMolecular Shapes, VSEPR Theory, and Hybridization

Complete the following statement regarding the molecular geometry and central atom hybridization of phosphorus pentachloride (PCl5PCl_5).

Answer:In a molecule of phosphorus pentachloride (PCl5PCl_5), the central phosphorus atom forms five bonding pairs with no lone pairs, resulting in a 【trigonal bipyramidal】 molecular shape and an 【sp3d】 hybridization state.

Answer

The molecular shape of phosphorus pentachloride (PCl5PCl_5) is trigonal bipyramidal, and the hybridization state of the central phosphorus atom is sp3dsp^3d.
Phosphorus in PCl5PCl_5 shares its 5 valence electrons with 5 chlorine atoms, forming 5 single covalent bonds with zero lone pairs. According to VSEPR theory, five valence electron pairs position themselves as far apart as possible in a trigonal bipyramidal arrangement (with 90° axial-equatorial and 120° equatorial-equatorial bond angles). The central phosphorus atom undergoes sp3dsp^3d hybridization by mixing one 3s, three 3p, and one 3d orbital to produce five sp3dsp^3d hybrid orbitals.

Step-by-Step Solution

1
Determine valence electron count and electron domains around the central phosphorus atom
Phosphorus (Group 15) has 5 valence electrons. In PCl5PCl_5, phosphorus forms 5 single covalent bonds with 5 chlorine atoms, yielding 5 bonding pairs and 0 lone pairs (total 5 electron domains).
VSEPR theory uses the total number of valence electron pairs (bonding pairs plus lone pairs) around the central atom to determine spatial arrangement.
2
Deduce the molecular shape and hybridization scheme for 5 electron domains
To minimize electrostatic repulsion, 5 electron domains adopt a trigonal bipyramidal geometry. Creating 5 equivalent hybrid orbitals requires mixing one s orbital, three p orbitals, and one d orbital, resulting in sp3dsp^3d hybridization.
Elements in Period 3 (like phosphorus) have accessible 3d orbitals allowing an expanded octet of 10 valence electrons.

Key Concept

VSEPR theory predictions and orbital hybridization for molecules with five valence electron pairs (sp3dsp^3d trigonal bipyramidal).
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Topics

Molecular Shapes, VSEPR Theory, and Hybridization

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