Question

What is the geometry of $\mathrm{SbF}_5$ molecule?

• A. Trigonal pyramidal
• B. Trigonal planar
• C. Square pyramidal
• D. Trigonal bipyramidal

Hint:

Any neutral central atom from Group 15 (like $\mathrm{P}$, $\mathrm{As}$, $\mathrm{Sb}$) bonded to exactly five monovalent halogen atoms ($\mathrm{X}_5$) will have a steric number of 5 with zero lone pairs, guaranteeing a trigonal bipyramidal molecular shape!

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to determine the molecular geometry of Antimony pentafluoride ($\mathrm{SbF}_5$) based on coordination principles.

Step 2: Key Formula or Approach:
We apply the Valence Shell Electron Pair Repulsion (VSEPR) theory. First, determine the steric number (SN) of the central atom using: $$\text{Steric Number} = \frac{1}{2} \left[ V + M - C + A \right]$$ Where $V$ is the number of valence electrons of the central atom, $M$ is the number of monovalent atoms, $C$ is the cationic charge, and $A$ is the anionic charge.

Step 3: Detailed Explanation:
Antimony ($\mathrm{Sb}$) belongs to Group 15 of the periodic table (nitrogen family), so it has $V = 5$ valence electrons.
The number of monovalent fluorine ligands surrounding it is $M = 5$. The molecule is neutral ($C = 0, A = 0$).
Calculate the steric number: $$\text{Steric Number} = \frac{1}{2} [5 + 5 - 0 + 0] = 5$$ A steric number of 5 indicates $\mathrm{sp^3d}$ hybridization of the central antimony atom.
Since there are 5 bonding pairs and no lone pairs ($5 - 5 = 0$) on the central atom, the molecule adopts a spatial arrangement that minimizes electron repulsion. According to VSEPR theory, this corresponds to a stable

trigonal bipyramidal geometry. In this structure, three fluorine atoms sit in an equatorial plane with $120^\circ$ separation, and two fluorine atoms stand in vertical axial positions at $90^\circ$ relative to the plane.

Step 4: Final Answer:
The geometry of the $\mathrm{SbF}_5$ molecule is trigonal bipyramidal, matching option (D).