Question:
What is the geometry of $PCl_5$ molecule as per VSEPR?
What is the geometry of $PCl_5$ molecule as per VSEPR?
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Chemistry Tip: Molecules with the general formula $AX_5E_0$ (where A is the central atom, X are bonded atoms, and E are lone pairs) always exhibit a trigonal bipyramidal shape.
Updated On: Apr 23, 2026
- Trigonal bipyramidal
- Octahedral
- Tetrahedral
- Square pyramidal
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The Correct Option is A
Solution and Explanation
Concept:
Chemistry (Chemical Bonding) - VSEPR Theory.
Step 1: Identify the central atom and its valence electrons. The central atom in the molecule is Phosphorus (P). Phosphorus is located in Group 15 of the periodic table, which means it has 5 valence electrons in its outermost shell.
Step 2: Determine the number of bond pairs (BP). The chemical formula $PCl_5$ indicates that the central phosphorus atom is bonded to 5 surrounding chlorine (Cl) atoms. Each bond is a single covalent bond. Therefore, the number of bond pairs (BP) is 5.
Step 3: Calculate the number of lone pairs (LP). The number of lone pairs on the central atom can be calculated by subtracting the number of shared electrons from the total valence electrons and dividing by two. Since all 5 valence electrons of phosphorus are used to form the 5 single bonds with chlorine, there are $5 - 5 = 0$ electrons remaining. Thus, the number of lone pairs (LP) is 0.
Step 4: Determine the steric number and electron geometry. The steric number is the sum of the bond pairs and lone pairs: $BP + LP = 5 + 0 = 5$. According to Valence Shell Electron Pair Repulsion (VSEPR) theory, a steric number of 5 corresponds to a trigonal bipyramidal electron geometry to minimize electron repulsion.
Step 5: Determine the final molecular geometry. Because there are zero lone pairs on the central phosphorus atom, there is no distortion to the underlying electron geometry. The arrangement of the atoms precisely follows the arrangement of the electron domains.
Therefore, the molecular geometry is identical to the electron geometry, which is perfectly trigonal bipyramidal, with three equatorial bonds at $120^\circ$ to each other and two axial bonds at $90^\circ$ to the equatorial plane. $$ \therefore \text{The geometry of the } PCl_{5} \text{ molecule is trigonal bipyramidal.} $$
Step 1: Identify the central atom and its valence electrons. The central atom in the molecule is Phosphorus (P). Phosphorus is located in Group 15 of the periodic table, which means it has 5 valence electrons in its outermost shell.
Step 2: Determine the number of bond pairs (BP). The chemical formula $PCl_5$ indicates that the central phosphorus atom is bonded to 5 surrounding chlorine (Cl) atoms. Each bond is a single covalent bond. Therefore, the number of bond pairs (BP) is 5.
Step 3: Calculate the number of lone pairs (LP). The number of lone pairs on the central atom can be calculated by subtracting the number of shared electrons from the total valence electrons and dividing by two. Since all 5 valence electrons of phosphorus are used to form the 5 single bonds with chlorine, there are $5 - 5 = 0$ electrons remaining. Thus, the number of lone pairs (LP) is 0.
Step 4: Determine the steric number and electron geometry. The steric number is the sum of the bond pairs and lone pairs: $BP + LP = 5 + 0 = 5$. According to Valence Shell Electron Pair Repulsion (VSEPR) theory, a steric number of 5 corresponds to a trigonal bipyramidal electron geometry to minimize electron repulsion.
Step 5: Determine the final molecular geometry. Because there are zero lone pairs on the central phosphorus atom, there is no distortion to the underlying electron geometry. The arrangement of the atoms precisely follows the arrangement of the electron domains.
Therefore, the molecular geometry is identical to the electron geometry, which is perfectly trigonal bipyramidal, with three equatorial bonds at $120^\circ$ to each other and two axial bonds at $90^\circ$ to the equatorial plane. $$ \therefore \text{The geometry of the } PCl_{5} \text{ molecule is trigonal bipyramidal.} $$
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