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NEET CHEMISTRYOrganic Chemistry – Some Basic Principles and Techniques Medium

Question

Given the following five species: NH3,AlCl3,BeCl2,CCl4,PCl5NH_3, AlCl_3, BeCl_2, CCl_4, PCl_5. The total number of these species that do not have eight electrons around the central atom in its/their outermost shell, is:

A

One

B

Three

C

Two

D

Four

Step-by-Step Solution

  1. Analyze the Octet Rule: The octet rule states that atoms tend to combine in such a way that they each have eight electrons in their valence shells. However, there are exceptions.
  2. Analyze each species:
  • NH3NH_3: Nitrogen has 5 valence electrons. It forms 3 sigma bonds with H and has 1 lone pair. Total electrons = 3×23 \times 2 (bonding) + 2 (lone pair) = 8 electrons. (Follows octet rule) .
  • AlCl3AlCl_3: Aluminum has 3 valence electrons. It forms 3 sigma bonds with Cl. Total electrons = 3×23 \times 2 = 6 electrons. (Incomplete octet, electron deficient) .
  • BeCl2BeCl_2: Beryllium has 2 valence electrons. It forms 2 sigma bonds with Cl. Total electrons = 2×22 \times 2 = 4 electrons. (Incomplete octet, electron deficient) .
  • CCl4CCl_4: Carbon has 4 valence electrons. It forms 4 sigma bonds with Cl. Total electrons = 4×24 \times 2 = 8 electrons. (Follows octet rule) .
  • PCl5PCl_5: Phosphorus has 5 valence electrons. It forms 5 sigma bonds with Cl. Total electrons = 5×25 \times 2 = 10 electrons. (Expanded octet/Hypervalent) .
  1. Count exceptions: The species that do not have 8 electrons are AlCl3AlCl_3 (6), BeCl2BeCl_2 (4), and PCl5PCl_5 (10).
  2. Conclusion: There are 3 such species.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Organic Chemistry – Some Basic Principles and Techniques . Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

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