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Chemical Bonding and Molecular Structure question

2022 · 28 Jun · Shift 2 · Q3
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Chemical Bonding and Molecular Structure question

2022 · 28 Jun · Shift 2 · Q3

JEE MainChemistryChemical Bonding and Molecular StructureMCQ+4 / −1
In the structure of SF4SF_4SF4​, the lone pair of electrons on S is in.
  1. A
    equatorial position and there are two lone pair - bond pair repulsions at 90 ∘^\circ∘.
  2. B
    equatorial position and there are three lone pair - bond pair repulsions at 90 ∘^\circ∘.
  3. C
    axial position and there are three lone pair - bond pair repulsion at 90 ∘^\circ∘.
  4. D
    axial position and there are two lone pair - bond pair repulsion at 90 ∘^\circ∘.
View written solutionFree

Correct answer: A

  1. Determine the electron pair geometry of SF4SF_4SF4​

Sulfur has 6 valence electrons. In SF4SF_4SF4​, sulfur forms 4 S−FS-FS−F bonds and has 1 lone pair.

So, the steric number is: 4+1=54 + 1 = 54+1=5

A steric number of 5 corresponds to a trigonal bipyramidal electron pair geometry.

  1. Possible positions for the lone pair

In a trigonal bipyramidal arrangement, there are:

  • 3 equatorial positions
  • 2 axial positions

According to VSEPR theory, a lone pair occupies the position where repulsions are minimum.

  1. Compare axial vs equatorial placement
  • If the lone pair is in an axial position, it will have three 90∘90^\circ90∘ interactions with the three equatorial bond pairs.
  • If the lone pair is in an equatorial position, it will have only two 90∘90^\circ90∘ interactions with the two axial bond pairs.

Since lone pair-bond pair repulsion is strong, the lone pair prefers the arrangement with fewer 90∘90^\circ90∘ repulsions.

Therefore, the lone pair occupies an equatorial position.

  1. Count the lone pair-bond pair repulsions at 90∘90^\circ90∘

With lone pair in equatorial position:

  • it is at 90∘90^\circ90∘ to the two axial bond pairs
  • it is at 120∘120^\circ120∘ to the two equatorial bond pairs

Hence, the number of lone pair-bond pair repulsions at 90∘90^\circ90∘ is 2.

  1. Evaluate options
  • A: equatorial position and there are two lone pair-bond pair repulsions at 90∘90^\circ90∘ ✅
  • B: equatorial position and there are three lone pair-bond pair repulsions at 90∘90^\circ90∘ ❌
  • C: axial position and there are three lone pair-bond pair repulsions at 90∘90^\circ90∘ ❌
  • D: axial position and there are two lone pair-bond pair repulsions at 90∘90^\circ90∘ ❌

So the correct option is A.

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