Problem 64 - Chemistry The Central Science

Question

Which of the following properties are typical characteristics of a covalent- network solid, a metallic solid, or both: (a) ductility, (b) hardness, (c) high melting point?

Step-by-Step Solution

Answer

\( \text{Ductility: Typical of Metallic Solids} \) \( \text{Hardness: Typical of Covalent-Network Solids} \) \( \text{High Melting Point: Typical of both Covalent-Network Solids and Metallic Solids} \)

Step 1: Understand characteristics of Covalent-Network Solids

Covalent-network solids have extended networks of atoms with covalent bonds. These bonds are strong and directional, and that's why these solids have some distinctive properties like high hardness, high melting point, and being non-conductors of electricity.

Step 2: Understand characteristics of Metallic Solids

Metallic solids have a lattice structure with atoms arranged in a continuous pattern. They have non-directional metallic bonding, where mobile electrons flow around the positively charged metal ions. These solids possess electrical conductivity, ductility, malleability, and usually a high melting point.

Step 3: Comparing Properties (a) Ductility

Ductility refers to the ability of a solid to sustain deformation under tensile stress or stretching. As metallic solids have non-directional metallic bonding, they can undergo deformation without breaking the bonds, thus, they are ductile. Covalent-network solids, on the other hand, have directional bonds that resist deformation, so they are not ductile. Therefore, ductility is a typical characteristic of metallic solids.

Step 4: Comparing Properties (b) Hardness

Hardness is the resistance of a material to penetration and plastic deformation. Covalent-network solids have strong and directional covalent bonds that resist penetration, making them extremely hard. Metals, however, show varied hardness levels depending on the type of metal and the strength of metallic bonds. For this question, hardness would typically be associated with covalent-network solids.

Step 5: Comparing Properties (c) High Melting Point

Both covalent-network solids and metallic solids often have a high melting point. Covalent-network solids have a high melting point due to their strong covalent bonds which need considerable energy to break. In metallic solids, the positive metal ions are surrounded by mobile electrons which require significant energy to disrupt, resulting in a high melting point. Therefore, high melting point is a common characteristic of both covalent-network and metallic solids. In summary: - Ductility: Typical of Metallic Solids - Hardness: Typical of Covalent-Network Solids - High Melting Point: Typical of both Covalent-Network Solids and Metallic Solids