Question

Which of these molecules have non-bonding electron pairs on the central atom?

• A. II only
• B. I and II only
• C. I and III only
• D. II and III

Hint:

When analyzing molecular geometry, consider the number of bonding and lone pairs on the central atom. Lone pairs contribute to the overall shape of the molecule and affect bond angles.

Answer 1

The Correct Option is D

To determine which molecules (SF₄, ICl₃, and SO₂) have non-bonding electron pairs on their central atoms, we'll analyze their Lewis structures.

1. Valence Electron Count:
- Sulfur (S): 6 valence electrons
- Iodine (I): 7 valence electrons
- Chlorine (Cl): 7 valence electrons
- Oxygen (O): 6 valence electrons
- Fluorine (F): 7 valence electrons

2. Lewis Structure Analysis:

SF₄:
- Central S forms 4 bonds with F atoms (using 8 electrons)
- S has 6 valence electrons → 2 remaining electrons (1 lone pair)
- Result: 1 lone pair on S

ICl₃:
- Central I forms 3 bonds with Cl atoms (using 6 electrons)
- I has 7 valence electrons → 4 remaining electrons (2 lone pairs)
- Result: 2 lone pairs on I

SO₂:
- Central S forms 2 bonds with O atoms (resonance structures)
- S has 6 valence electrons → 4 remaining electrons (1 lone pair)
- Result: 1 lone pair on S

3. Summary of Lone Pairs:
- SF₄: 1 lone pair on S
- ICl₃: 2 lone pairs on I
- SO₂: 1 lone pair on S

Final Answer:
All three molecules (I. SF₄, II. ICl₃, and III. SO₂) have non-bonding electron pairs on their central atoms. The correct choice is D. I, II and III.

Answer 2

To determine which molecules have lone pairs on their central atoms, we'll analyze their electronic structures and bonding patterns.

1. Fundamental Concepts:
The octet rule states that atoms tend to form bonds to achieve 8 valence electrons. However, elements in period 3 and below (like S and I) can exceed the octet rule due to available d-orbitals.

2. Molecular Analysis:

SF₄ (Sulfur Tetrafluoride):
- Central S: 6 valence electrons
- Each F: 7 valence electrons
- Total valence electrons: 6 + (4×7) = 34
- S forms 4 single bonds with F atoms (using 8 electrons)
- Remaining electrons: 34 - 8 = 26 (distributed as lone pairs on F atoms)
- Key point: S has 1 lone pair after forming 4 bonds (10 electrons total around S)

ICl₃ (Iodine Trichloride):
- Central I: 7 valence electrons
- Each Cl: 7 valence electrons
- Total valence electrons: 7 + (3×7) = 28
- I forms 3 single bonds with Cl atoms (using 6 electrons)
- Remaining electrons: 28 - 6 = 22 (distributed as lone pairs)
- Key point: I has 2 lone pairs after forming 3 bonds (10 electrons total around I)

SO₂ (Sulfur Dioxide):
- Central S: 6 valence electrons
- Each O: 6 valence electrons
- Total valence electrons: 6 + (2×6) = 18
- S forms 1 double bond and 1 single bond (with coordinate bond)
- Key point: S has 1 lone pair in the most stable resonance structure

3. Conclusion:
All three molecules feature lone pairs on their central atoms:
- SF₄: 1 lone pair on S
- ICl₃: 2 lone pairs on I
- SO₂: 1 lone pair on S

Final Answer:
The correct choice is D. I, II and III, as all three molecules have non-bonding electron pairs on their central atoms.