The space model which is obtained by joining the points representing various bonded atoms gives the shape of the molecule. The geometry of the molecule is definite relative arrangement of the bonded atoms in a molecule. The shape and geometry of a molecule is explained by valence shell electron pair repulsion theory given by Gillespie and Nyholm.
Which molecule has both shape and geometry identical ?
`(I) SnCl_(2) " " (II) NH_(3) " " (III) PCl_(5) " " (IV) SF_(6)`

Options

A. I, III and IV
B. II,III and IV
C. III and IV
D. All

Answer

To determine which molecule has both shape and geometry that are identical among the given options (I) SnCl₂, (II) NH₃, (III) PCl₅, and (IV) SF₆, we will analyze each molecule based on the Valence Shell Electron Pair Repulsion (VSEPR) theory.

### Step-by-Step Solution:

1. **Analyze SnCl₂:**
- **Valence Electrons:** Sn (Tin) is in group 14 and has 4 valence electrons. Each Cl (Chlorine) contributes 1 electron, so total = 4 + 2 = 6 electrons.
- **Bonding and Lone Pairs:** SnCl₂ has 2 bond pairs (from 2 Cl atoms) and 1 lone pair on Sn.
- **Steric Number:** The steric number is 3 (2 bond pairs + 1 lone pair).
- **Geometry:** With a steric number of 3, the geometry is trigonal planar.
- **Shape:** The presence of a lone pair makes the shape bent or V-shaped.
- **Conclusion:** Shape (bent) and geometry (trigonal planar) are not identical.

2. **Analyze NH₃:**
- **Valence Electrons:** N (Nitrogen) is in group 15 and has 5 valence electrons. Each H (Hydrogen) contributes 1 electron, so total = 5 + 3 = 8 electrons.
- **Bonding and Lone Pairs:** NH₃ has 3 bond pairs (from 3 H atoms) and 1 lone pair on N.
- **Steric Number:** The steric number is 4 (3 bond pairs + 1 lone pair).
- **Geometry:** With a steric number of 4, the geometry is tetrahedral.
- **Shape:** The presence of a lone pair makes the shape trigonal pyramidal.
- **Conclusion:** Shape (trigonal pyramidal) and geometry (tetrahedral) are not identical.

3. **Analyze PCl₅:**
- **Valence Electrons:** P (Phosphorus) is in group 15 and has 5 valence electrons. Each Cl contributes 1 electron, so total = 5 + 5 = 10 electrons.
- **Bonding and Lone Pairs:** PCl₅ has 5 bond pairs and 0 lone pairs.
- **Steric Number:** The steric number is 5 (5 bond pairs + 0 lone pairs).
- **Geometry:** With a steric number of 5, the geometry is trigonal bipyramidal.
- **Shape:** Since there are no lone pairs, the shape is also trigonal bipyramidal.
- **Conclusion:** Shape (trigonal bipyramidal) and geometry (trigonal bipyramidal) are identical.

4. **Analyze SF₆:**
- **Valence Electrons:** S (Sulfur) is in group 16 and has 6 valence electrons. Each F (Fluorine) contributes 1 electron, so total = 6 + 6 = 12 electrons.
- **Bonding and Lone Pairs:** SF₆ has 6 bond pairs and 0 lone pairs.
- **Steric Number:** The steric number is 6 (6 bond pairs + 0 lone pairs).
- **Geometry:** With a steric number of 6, the geometry is octahedral.
- **Shape:** Since there are no lone pairs, the shape is also octahedral.
- **Conclusion:** Shape (octahedral) and geometry (octahedral) are identical.

### Final Conclusion:
The molecules that have both shape and geometry identical are **(III) PCl₅** and **(IV) SF₆**.