47. Which of the following diagrams best illustrates how a displacement in an ionic crystal results — Bonding Chemistry Question

STEPS:

1. Understand the nature of bonding and structure in ionic solids: Ionic solids are held together by strong, highly directional electrostatic attractions (ionic bonds) between alternating cations (positive ions) and anions (negative ions) arranged in a three-dimensional crystal lattice. In a stable ionic lattice, each positive ion is surrounded by negative ions, and each negative ion is surrounded by positive ions, maximizing attractive forces and minimizing repulsive forces.
2. Analyze what happens when an external force is applied (displacement): When an ionic crystal is subjected to mechanical stress (such as being struck with a hammer), a plane of ions is forced to slide or displace relative to the adjacent plane.
3. Determine the electrostatic consequence of this displacement: Shifting a layer of the crystal by even a single ionic diameter causes ions of like charges to align directly across from one another (i.e., positive ions align with positive ions, and negative ions align with negative ions).
4. Relate this charge alignment to cleavage and brittleness: Because like charges repel, the sudden alignment of positive-positive and negative-negative charges results in massive electrostatic repulsion between the two adjacent layers. This repulsive force instantaneously drives the layers apart, causing the crystal to split cleanly along a flat plane (known as cleavage) and shatter, which represents the property of brittleness.
5. Identify the correct diagram: Diagram A perfectly illustrates this physical mechanism. The "Before Displacement" view shows a stable alternating grid of positive and negative charges. The "After Displacement" view shows that the applied force has shifted the top layer, aligning like charges (+ next to +, and - next to -) directly opposite each other, driving the layers apart and creating a cleavage gap.

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WHY_OTHERS_WRONG:

• Diagrams B and C are incorrect: These diagrams do not show a standard alternating ionic lattice of cations and anions. Instead, they depict a lattice of large spheres with smaller positive spheres occupying the interstitial gaps (resembling a covalent or interstitial network). They fail to clearly show the fundamental periodic alignment of like charges and subsequent electrostatic repulsion that explains the mechanical cleavage of standard ionic crystals.
• Diagram D is incorrect: This diagram represents a metallic crystal lattice, which consists of positive metal cores surrounded by a mobile "sea of valence electrons". When a metallic lattice is displaced, the mobile electrons freely flow and adjust to the new positions of the positive cations to maintain the nondirectional metallic bonds. This allows the metal to deform rather than shatter, explaining why metals are malleable and ductile instead of brittle.