bond angles, molecular geometry, electron geometry, and electron groups of central atom PCl3
The correct answer and explanation is:
Correct Answer for PCl₃ (Phosphorus Trichloride):
- Bond Angles: Approximately 107°
- Molecular Geometry: Trigonal pyramidal
- Electron Geometry: Tetrahedral
- Electron Groups on Central Atom (P): 4 (3 bonding pairs + 1 lone pair)
300-Word Explanation:
Phosphorus trichloride (PCl₃) is a molecular compound consisting of one phosphorus (P) atom covalently bonded to three chlorine (Cl) atoms. To understand its structure and shape, we analyze it using Valence Shell Electron Pair Repulsion (VSEPR) theory.
Phosphorus has five valence electrons. In PCl₃, it uses three of these electrons to form single covalent bonds with three chlorine atoms. This leaves one lone pair of electrons on the phosphorus atom. Therefore, the central atom (P) has four electron groups: three bonding pairs (P–Cl bonds) and one lone pair.
The electron geometry considers all electron groups (both bonding and lone pairs), which leads to a tetrahedral arrangement because four electron groups orient themselves to minimize repulsion in three-dimensional space.
However, the molecular geometry considers only the positions of atoms (not lone pairs). Since one of the four groups is a lone pair, the molecular shape becomes trigonal pyramidal, with the lone pair pushing the three P–Cl bonds downward.
The bond angle in a perfect tetrahedron is 109.5°, but the presence of a lone pair—which exerts more repulsive force than bonding pairs—slightly reduces the bond angle to approximately 107° in PCl₃.
In summary:
- The tetrahedral electron geometry reflects the arrangement of all electron regions.
- The trigonal pyramidal molecular geometry results from only considering the atoms’ positions.
- The lone pair affects the bond angle, making it less than the ideal tetrahedral angle.
This VSEPR-based approach helps chemists predict and understand molecular shapes and reactivity.