Q.Define the term 'amorphous'. Give a few examples of amorphous solids.

An amorphous solid consists of particles of irregular shape in which the arrangement of constituent particles has only short-range order and no long-range order. They are isotropic, have no sharp melting point, and are regarded as super-cooled liquids (pseudo-solids).

Definition.

An amorphous solid (Greek amorphos = no form) is one in which the constituent particles (atoms, ions or molecules) are arranged in an irregular manner. There is order in the arrangement of particles only over short distances (short-range order), but no regularity over long distances (no long-range order).

Characteristic properties.

• Isotropic — physical properties (refractive index, conductivity) are the same in all directions.
• No sharp melting point — they soften over a range of temperature.
• Irregular cleavage — break into pieces with irregular surfaces.
• Regarded as super-cooled liquids / pseudo-solids because they can flow very slowly.

Examples.

Glass ($SiO_2$-based), rubber, plastics (e.g. polythene, PVC), fused silica, coal, tar.

State the definition around the key discriminator — absence of long-range order — then list everyday non-crystalline solids as examples.

• Saying amorphous solids have "no order at all"; they do have short-range order.
• Confusing amorphous with crystalline properties (sharp m.p., anisotropy).
• Giving crystalline substances (NaCl, quartz) as examples.