Van der Waals (molecular) crystals and electron shells Evaluate the statement: “In van der Waals crystals (e.g., rare-gas solids and many molecular crystals), there exists a high degree of stability of the outer electron shell.” Indicate whether it is true or false and explain in terms of bonding and electronic structure.

Introduction / Context:
Crystals can be classified by their dominant bonding: ionic, covalent, metallic, hydrogen-bonded, and van der Waals (molecular). Van der Waals crystals are composed of atoms or molecules whose outer electron shells are largely closed and chemically inert, with the solid held together by weak intermolecular forces rather than strong ionic or covalent bonds.

Given Data / Assumptions:

• Examples: solid noble gases (Ar, Kr, Xe), molecular solids such as solid N2 or CH4 under suitable conditions.
• Outer valence shells are complete (closed-shell configurations) or tightly bound within molecules.
• Intermolecular bonding is via induced dipole–induced dipole (London dispersion) and related weak interactions.

Concept / Approach:

Because constituent atoms/molecules in van der Waals solids have stable, closed outer electron shells, they do not readily form strong directional bonds. The crystalline cohesion is dominated by weak dispersion forces arising from instantaneous dipoles. Hence their electronic bands are narrow, band gaps are large (insulating behavior), melting/boiling points are low, and chemical reactivity is minimal—all consistent with highly stable outer shells.

Step-by-Step Solution:

Verification / Alternative check:

Noble gases crystallize at low temperatures without forming chemical bonds; their filled valence shells account for chemical inertness and weak cohesive energies.

Why Other Options Are Wrong:

Claiming “False” contradicts the defining feature of van der Waals crystals; restricting truth to low temperature or to ionic crystals misunderstands the role of electron shell stability.

Common Pitfalls:

Confusing molecular crystals with covalent network solids (e.g., diamond) where strong covalent bonds dominate; assuming weak bonding implies unstable electron shells (it is the opposite).

Final Answer:

True