Question

Indicate the type of solid (molecular, metallic, ionic, or covalent-network) for each compound: (a) SiC, (b) $\mathrm{Ni}$ (c) ${\mathrm{CaCl}}_2$ (d) camphor $\left({\mathrm{C}}_{10}{\mathrm{H}}_{16}\mathrm{O}\right)$, (e) ${\mathrm{SiO}}_2$.

Short answer

The types of solids for each compound are: (a) SiC - Covalent-network solid (b) Ni - Metallic solid (c) CaCl2 - Ionic solid (d) Camphor (C10H16O) - Molecular solid (e) SiO2 - Covalent-network solid

Step-by-step solution

Identify the types of elements in the compound (a) SiC

Silicon (Si) is a metalloid and Carbon (C) is a non-metal. Both of them tend to form covalent bonds. In this compound, Si and C form a covalent-network solid due to the strong covalent bonds between them.

Identify the types of elements in the compound (b) Ni

Nickel (Ni) is a metal. Thus, nickel forms metallic bonds with itself and leads to the formation of a metallic solid.

Identify the types of elements in the compound (c) CaCl2

Calcium (Ca) is a metal and chlorine (Cl) is a non-metal. In this compound, metal and non-metal elements are combined, leading to the formation of ionic bonds. Hence, CaCl2 is an ionic solid.

Identify the types of elements in the compound (d) camphor (C10H16O)

The elements in camphor are carbon (C), hydrogen (H), and oxygen (O), which are all non-metals. Therefore, the bonds formed between these elements are covalent. Since camphor is a complex organic molecule, it forms a molecular solid.

Identify the types of elements in the compound (e) SiO2

Silicon (Si) is a metalloid and oxygen (O) is a non-metal. These elements form covalent bonds. In this compound, Si and O form a covalent-network solid due to the strong covalent bonds between them. In conclusion, the types of solids for each compound are: (a) SiC - Covalent-network solid (b) Ni - Metallic solid (c) CaCl2 - Ionic solid (d) Camphor (C10H16O) - Molecular solid (e) SiO2 - Covalent-network solid

Key concepts

Covalent-network solid

Covalent-network solids are fascinating because they are made up of a continuous network of covalent bonds between atoms. This results in incredibly strong materials with very high melting points.
Covalent bonds form when two atoms share electrons to achieve stability, and when these bonds extend throughout a structure, it turns into a covalent-network solid.
Common examples are diamond and silicon carbide (SiC).

• Hardness and Strength: Due to the strong covalent bonds, these solids are usually very hard and robust.
• High Melting Points: The continuous network of bonds gives them high thermal resilience.
• Poor Conductors: They don’t conduct electricity well, as there are no free charge carriers.

In these solids, every atom is bonded to several neighbors in a three-dimensional network forming a single giant molecule, making them unique and durable.

Metallic solid

Metallic solids are unique in that they exhibit a structure characterized by a sea of delocalized electrons surrounding a lattice of metal cations. This structure gives rise to properties like malleability, ductility, and conductivity.
Metals like nickel (Ni) exemplify this type of solid.

• Electrical Conductivity: The presence of free electrons allows metals to conduct electricity efficiently.
• Thermal Conductivity: Metals also conduct heat well due to electron mobility.
• Malleability and Ductility: The ability of metal atoms to roll over each other without breaking bonds makes metallic solids flexible.

These solids have a distinctive shine or luster, attributable to the electron flow across the surface, which makes them reflective.

Ionic solid

Ionic solids are formed from ions, which are atoms or molecules with an electric charge. Typically, this involves metals forming positive ions and non-metals forming negative ions.
The electrostatic attraction between oppositely charged ions results in a highly ordered and stable structure.

• High Melting and Boiling Points: A lot of energy is required to overcome the strong attractive forces between ions.
• Electrical Conductivity: These solids conduct electricity when melted or dissolved in water, as the ions are free to move.
• Brittleness: While generally strong, applying force can lead to repulsion between like-charged ions, causing the solid to shatter.

Examples include calcium chloride (CaCl₂), where calcium forms cations and chlorine forms anions, creating strong ionic bonds that define the solid's properties.

Molecular solid

Molecular solids are composed of molecules held together by relatively weak intermolecular forces, such as van der Waals forces or hydrogen bonds. These bonds are much weaker than covalent or ionic bonds, which leads to softer solids and lower melting points.
Camphor ( Molecular solids are intriguing because they can exist in different physical states and are sensitive to changes in pressure and temperature.

• Low Melting Points: Due to weak intermolecular forces, these solids often melt at relatively low temperatures.
• Poor Conductors: They lack free charge carriers, which makes them bad conductors of electricity.
• Variable Hardness: The strength can vary widely, depending on the type of molecules and the intermolecular forces.

Molecular solids like camphor (C₁₀H₁₆O) can be quite different from each other in appearance and feel, depending significantly on the nature of forces between their molecules.