Determine the electron geometry (eg) and molecular geometry (mg) of PCl5. eg = trigonal bipyramidal, mg = trigonal pyramidal eg = trigonal bipyramidal, mg = trigonal bipyramidal eg = tetrahedral, mg = octahedral eg = trigonal planar, mg = octahedral eg = octahedral, mg = tetrahedral 2
The Correct Answer and Explanation is:
The correct answer is:
Electron Geometry (eg) = Trigonal Bipyramidal, Molecular Geometry (mg) = Trigonal Bipyramidal
Explanation:
Phosphorus pentachloride (PCl₅) consists of a central phosphorus atom surrounded by five chlorine atoms. Let’s break it down:
- Electron Geometry (eg):
- PCl₅ has 5 bonding pairs of electrons around the central phosphorus atom. In a molecule with 5 electron pairs, the electron geometry adopts a trigonal bipyramidal shape. This arrangement minimizes electron pair repulsion, as predicted by VSEPR theory (Valence Shell Electron Pair Repulsion theory).
- In this geometry, there are 3 positions that form an equatorial plane (in the same horizontal plane), and 2 axial positions (above and below this plane).
- Molecular Geometry (mg):
- Since all five positions around the phosphorus atom are occupied by chlorine atoms, there is no lone pair on the phosphorus atom.
- Therefore, the molecular geometry also remains trigonal bipyramidal because there are no deviations caused by lone pairs. If there were lone pairs, they would cause distortions, but in this case, the geometry remains symmetric.
VSEPR Theory Insight:
- The 5 bonding pairs of electrons in PCl₅ result in a geometry that minimizes repulsion and maximizes stability.
- The trigonal bipyramidal shape allows the bonds to be as far away from each other as possible, with bond angles of 90° between axial and equatorial positions and 120° between the equatorial bonds.
Thus, the answer is:
Electron Geometry (eg) = Trigonal Bipyramidal, Molecular Geometry (mg) = Trigonal Bipyramidal.
