The difference between metals and glass that causes metals to melt at high temperatures while glass does not primarily lies in their atomic or molecular structures and bonding.
Metals: Metals are characterized by their metallic bonding, which involves the delocalization of valence electrons over a lattice of positively charged metal ions. This delocalized electron sea allows metals to conduct heat and electricity efficiently. When metals are heated, the increased thermal energy causes the metal ions to vibrate more vigorously. As the temperature rises, these vibrations become more energetic, eventually overcoming the attractive forces between the metal ions. At a specific temperature known as the melting point, the metal ions break free from their fixed positions, transitioning from a solid to a liquid state.
Glass: Glass, on the other hand, is an amorphous solid, meaning it lacks a long-range ordered crystalline structure. Unlike metals, glass does not have a distinct melting point. Instead, it undergoes a gradual softening and transition to a more viscous state when heated. Glass is typically composed of a network of silicon dioxide (SiO2) or other compounds, and its atoms or molecules are arranged in a disordered manner.
The absence of a well-defined crystalline structure in glass means that it lacks the regular repeating pattern of atoms found in metals. This arrangement makes the atoms or molecules in glass less able to overcome their bonding and move freely when heated. As a result, instead of melting at a specific temperature, glass gradually softens and becomes increasingly malleable as the temperature rises. Eventually, at very high temperatures, glass can undergo a transition to a supercooled liquid or transform into a different state, such as a gas, depending on the specific composition and conditions.
In summary, metals have a regular, crystalline structure with delocalized electrons, which allows them to melt at specific temperatures due to the breaking of metallic bonds. Glass, being an amorphous solid with a disordered atomic arrangement, lacks a distinct melting point and instead softens gradually when heated.