Question

The hybridisation scheme for the central atom includes a d-orbital contribution in

• A. I\(_3^-\)
• B. PCl\(_3\)
• C. NO\(_3^-\)
• D. H\(_2\)Se

Hint:

Hybridisation involving d-orbitals occurs in molecules with central atoms from period 3 and beyond.

Answer 1

The Correct Option is A

Step 1: {Hybridisation of I\(_3^-\)}
I\(_3^-\) is linear with the central iodine atom undergoing \(sp^3d\)-hybridisation and three lone pairs occupying the equatorial position. Thus, this structure includes a d-orbital contribution to the hybridisation scheme. Hence, the correct answer is (A).

Answer 2

Step 1: Understand the concept of hybridisation involving d-orbitals
When the central atom has more than 8 electrons in its valence shell (expanded octet), it often utilizes vacant d-orbitals for hybridisation.
This occurs commonly in elements of the 3rd period or beyond (like P, S, Cl, Br, I), which have available 3d, 4d, or 5d orbitals.

Step 2: Analyze the given ion – I₃⁻ (triiodide ion)
- Central atom: Iodine (I)
- Total valence electrons = 7 (from central I) + 2×7 (from terminal I atoms) + 1 (negative charge) = 22 electrons
- 2 bonds (with the terminal iodine atoms)
- Remaining electrons: 22 – 2×2 (bond pairs) = 18 electrons = 9 lone pairs → 3 lone pairs on each atom
- Central atom has 3 lone pairs and 2 bond pairs = 5 regions of electron density
- Hence, hybridisation = sp³d
- In sp³d, the d-orbital contributes to hybridisation

Step 3: Geometry and bonding
- The sp³d hybridisation leads to a linear molecular geometry
- The lone pairs occupy equatorial positions to minimize repulsion

Step 4: Final Answer
The hybridisation of the central atom in I₃⁻ includes d-orbital contribution:
I₃⁻