Rubber and glass have different molecular structures, which contribute to their different properties at room temperature.
Rubber is composed of long polymer chains, typically made of repeating units of carbon and hydrogen atoms. These polymer chains are coiled and entangled, allowing rubber to be elastic. At room temperature, the polymer chains are in a relatively relaxed state and have enough thermal energy to move and slide past each other when a force is applied. When the force is removed, the polymer chains return to their original state, giving rubber its elasticity.
On the other hand, glass is an amorphous solid, lacking a regular crystalline structure. It is typically composed of silica (silicon dioxide) and other additives. In glass, the atoms or molecules are not arranged in an ordered pattern, as they are in a crystalline solid. This lack of long-range order makes glass rigid and not easily deformable. At room temperature, the atoms or molecules in glass are frozen in place and do not have the mobility to move or slide past each other like the polymer chains in rubber. This lack of mobility is why glass is not elastic.
It's important to note that there are different types of glass with varying compositions and properties. Some types of glass, such as certain types of tempered glass or glass fibers, can exhibit some degree of elasticity due to specific manufacturing processes or additives. However, in general, traditional glass is not elastic at room temperature due to its amorphous nature.