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100

Fill in the blank with the correct words.

  1. According to VSEPR Theory, electron pairs around a central atom arrange themselves to minimize _____________.

  2. The shape of a molecule with four bonding pairs and no lone pairs around the central atom is called _____________.

  3. A molecule with two bonding pairs and two lone pairs on the central atom will have a _____________ shape.

  4. In the VSEPR model, lone pairs of electrons take up _____________ space than bonding pairs.

  5. The bond angle in a linear molecule like carbon dioxide (CO2)is _____________ degrees.

1. repulsion

2. Tetrahedral

3. Bent

4. Large

5. 180

200

Assertion : Lone pair-lone pair repulsive interactions are greater than lone pair-bond pair and bond pair-bond pair interactions. 

Reason : The space occupied by lone pair electrons is more as compared to bond pair electrons.

  1. Assertion is correct, reason is correct; reason is  correct explanation for assertion.
  2. Assertion is correct, reason is correct; reason is not the correct explanation for assertion
  3. Assertion is correct, reason is incorrect
  4. Assertion is incorrect, reason is correct

a. Assertion is correct, reason is correct; reason is  correct explanation for assertion.

300

Arrange the following in order of increasing bond angle:
BeCl2,NH₃, CH₄,H₂O

H₂O< NH₃<CH₄<BeCl2

400

Bond angle in ammonia differ from those in methane even though both have a tetrahedral electron-pair geometry. Give reason.

The bond angle in ammonia (107.3°) is smaller than in methane (109.5°) because ammonia's central nitrogen atom has one lone pair of electrons, whereas methane's central carbon atom has no lone pairs. This lone pair in ammonia exerts a stronger repulsion than the bond pairs, pushing the hydrogen atoms closer together and reducing the H-N-H bond angle from the ideal tetrahedral 109.5°.

500

A pharmaceutical research lab is developing a new drug molecule that includes several atoms bonded in different geometrical arrangements. One of the chemists is analyzing a fragment of the molecule containing the following central atoms and their surrounding atoms:

  • Atom A is bonded to 2 other atoms and has 2 lone pairs.

  • Atom B is bonded to 3 atoms and has 1 lone pair.

  • Atom C is bonded to 4 atoms and has no lone pairs.

  • Atom D is bonded to 2 atoms and has no lone pairs.

  • Atom E is bonded to 5 atoms and has no lone pairs.

The team wants to determine the 3D shapes of these molecular fragments to assess how they will interact with biological receptors.

Using the Valence Shell Electron Pair Repulsion (VSEPR) theory, answer the following:

  1. Determine the geometry and shape  for each of the atoms A to E.

  2. Explain how lone pairs affect molecular geometry in the cases where they are present.

  3. Which of these atoms (A–E) would have bond angles closest to 109.5°? Justify your answer.

  4. Suggest a real-world molecule or ion for each of the geometries identified.


1. Atom A - Geometry -Tetrahedral ;Shape-Bent

Atom B- Geometry -Tetrahedral ;Shape-Trigonal                   pyramidal

Atom C-Tetrahedral

Atom D-Linear

Atom E- Trigonal bipyramidal

2. Lone pairs distort molecular geometry by exerting stronger repulsive forces than bonding pairs, pushing bonded atoms closer together and reducing bond angle.

3. Atom C

4. Atom A-Water

   Atom B-Ammonia

Atom C -methane

Atom D-Beryllium chloride

Atom E-PCl5