Rank the following 3 classes of materials in order of increasing typical Young's Modulus: metals such as copper, plastics such as HDPE (high density polyethelene), and ceramics such as alumina (Al2O3). Do not look up the values of Young's Modulus, instead base your answer on what you know about the structure and chemistry of these classes of materials.

To rank these three classes of materials in order of increasing typical Young's Modulus, we need to consider their structural and chemical properties.

Metals, such as copper, have a crystalline structure with metallic bonding. Metallic bonds are formed by the delocalized electrons that allow for good electrical and thermal conductivity. This delocalization of electrons also gives metals their characteristic malleability and ductility. Due to the presence of mobile electrons, metals generally exhibit high values of Young's Modulus.

Ceramics, such as alumina (Al2O3), have a crystalline structure and are composed of ionic bonds. These bonds are formed by the electrostatic attraction between positively and negatively charged ions. Ceramics have a high melting point, are brittle, and have poor electrical and thermal conductivity. Typically, they exhibit a higher value of Young's Modulus compared to plastics but lower than metals.

Plastics, such as HDPE (high-density polyethylene), have a non-crystalline or semi-crystalline structure and are composed of long chains of carbon and hydrogen atoms (polymers). Plastics have weak intermolecular forces between these polymer chains, resulting in low stiffness and low values of Young's Modulus. They are generally flexible, lightweight, and have good electrical insulation properties.

Based on this understanding of the structural and chemical properties of these three classes of materials, we can rank them in order of increasing typical Young's Modulus:

1. Plastics such as HDPE (low Young's Modulus)
2. Ceramics such as alumina (medium Young's Modulus)
3. Metals such as copper (high Young's Modulus)

Please note that the exact values of Young's Modulus for specific materials within each class may vary, and it is always recommended to refer to reliable sources for accurate and precise values.