Atomic Arrangement — Identifying Amorphous Materials A material whose atoms lack long-range periodic order and are arranged in a disordered (chaotic) manner is termed:

Introduction / Context:Atomic ordering dictates many macroscopic properties such as elastic modulus, optical transparency, and diffusion. Materials are broadly classed as crystalline (long-range order) or amorphous (no long-range order). Some show partial order (liquid crystals), but the question asks for fully disordered arrangements.

Given Data / Assumptions:

• Atoms are arranged “chaotically,” i.e., no long-range periodicity.
• We are to name the category of such a material.
• Conventional materials science terminology applies.

Concept / Approach:Amorphous materials (e.g., common window glass, many polymers in the amorphous state, metallic glasses) lack translational long-range order. In contrast, crystalline materials have repeating unit cells forming a lattice with long-range periodicity. “Mesomorphous” refers to intermediate order as in liquid crystals, not fully chaotic solids.

Step-by-Step Solution:Match description (no long-range order) to term “amorphous.”Exclude “crystalline” which implies a periodic lattice.Exclude “mesomorphous,” which describes partial ordering phases.

Verification / Alternative check:X-ray diffraction of amorphous materials shows broad halos instead of sharp Bragg peaks, confirming absence of long-range order.

Why Other Options Are Wrong:Crystalline: contradicts the “chaotic” description.Mesomorphous: indicates partial, directional order (liquid crystals), not fully disordered solids.Polytypic: concerns different stacking sequences in layered crystals; still crystalline.

Common Pitfalls:Assuming glass must be crystalline because it is solid; many glasses are amorphous solids.

Final Answer:amorphous material