Problem 13 - Chemistry: The Central Science

Question

Indicate the type of solid (molecular, metallic, ionic, or covalent-network) for each compound: (a) \(\mathrm{CaCO}_{3}\), (b) \(\mathrm{Pt}\), (c) \(\mathrm{ZrO}_{2}\) (melting point, \(\left.2677^{\circ} \mathrm{C}\right)\), (d) table sugar \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\), (e) benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\), (f) \(\mathrm{I}_{2}\).

Step-by-Step Solution

Answer

The types of solids for the given compounds are: (a) \(\mathrm{CaCO}_{3}\): \[\textbf{Ionic}\] (b) \(\mathrm{Pt}\): \[\textbf{Metallic}\] (c) \(\mathrm{ZrO}_{2}\): \[\textbf{Ionic}\] (d) \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) (table sugar): \[\textbf{Molecular}\] (e) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (benzene): \[\textbf{Molecular}\] (f) \(\mathrm{I}_{2}\): \[\textbf{Molecular}\]

Step 1: Recognizing Compound Type

Since calcium is a metal, and carbonate (CO3) is polyatomic ion, this is an ionic compound, as it is formed by the transfer of electrons between the metal and non-metal.

Step 2: Solution

For \(\mathrm{CaCO}_{3}\), the type of solid is: \[\textbf{Ionic}\] (b) \(\mathrm{Pt}\)

Step 3: Recognizing Element Type

Platinum (Pt) is a metal, and metallic solids are formed when metal atoms are closely packed and held together by metallic bonds.

Step 4: Solution

For \(\mathrm{Pt}\), the type of solid is: \[\textbf{Metallic}\] (c) \(\mathrm{ZrO}_{2}\)

Step 5: Recognizing Compound Type

Zirconium (Zr) is a metal, and Oxygen (O) is a non-metal, which means this is a compound with ionic bonding between the metal and non-metal.

Step 6: Solution

For \(\mathrm{ZrO}_{2}\), the type of solid is: \[\textbf{Ionic}\] (d) \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\)

Step 7: Recognizing Compound Type

The molecule is composed only of non-metal atoms, which means it forms a molecular solid. Molecular solids are formed by individual molecules held together by weaker van der Waals forces or hydrogen bonds.

Step 8: Solution

For table sugar \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\), the type of solid is: \[\textbf{Molecular}\] (e) \(\mathrm{C}_{6} \mathrm{H}_{6}\)

Step 9: Recognizing Compound Type

Benzene, similar to table sugar, is composed only of non-metal atoms. The molecules are held together by weaker van der Waals forces in a molecular solid.

Step 10: Solution

For benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\), the type of solid is: \[\textbf{Molecular}\] (f) \(\mathrm{I}_{2}\)

Step 11: Recognizing Element Type

Iodine (I) is a non-metal that exists as diatomic molecules composed of two iodine atoms, which are held together by van der Waals forces in molecular solids.

Step 12: Solution

For \(\mathrm{I}_{2}\), the type of solid is: \[\textbf{Molecular}\]

Key Concepts

Molecular Solids

Molecular solids are an interesting type of solid where the key components are molecules rather than atoms or ions. These molecules are held together by relatively weak forces, primarily van der Waals forces or hydrogen bonds. These intermolecular forces are much weaker compared to ionic or covalent bonds, which is why molecular solids tend to have lower melting points.

Here are some key points about molecular solids:

• They have low melting and boiling points compared to other types of solids.
• Their structures are usually soft and more easily disrupted.
• Common examples include substances like dry ice ( CO_2), iodine ( I_2), and table sugar ( C_{12}H_{22}O_{11}).
• They are often poor conductors of electricity due to the absence of free electrons or ions.

Understanding molecular solids is crucial as they form the basis of many organic compounds and are prevalent in everyday materials like sugar and plastic.

Ionic Solids

Ionic solids are fascinating due to the strong electrostatic forces between their ions. These solids form when positive and negative ions come together in a lattice structure, each type of ion being attracted to its oppositely charged neighbors. Because of these strong attractions, ionic solids are incredibly stable and usually have high melting points.

Notable features of ionic solids include:

• Possessing high melting and boiling points due to the strength of ionic bonds.
• Lattice structures that are rigid and well-organized.
• Typically hard but brittle due to the slipping of planes of ions past each other.
• In their solid state, they don't conduct electricity. However, when dissolved in water or molten, they become excellent conductors as the ions are free to move.
• Common examples include sodium chloride (salt, NaCl) and calcium carbonate ( CaCO_3).

Ionic solids are fundamental in understanding not only many natural minerals and salts but also in industrial and laboratory applications.

Metallic Solids

Metallic solids stand out due to their unique bonding and structural properties. Composed entirely of metallic atoms, these solids are characterized by a "sea of electrons" that move freely among a lattice of metal cations. This delocalization of electrons explains many of the distinctive physical properties of metals.

Key characteristics of metallic solids include:

• They are excellent conductors of electricity and heat due to the mobility of the electrons.
• Metallic solids are typically ductile and malleable, meaning they can be drawn into wires and hammered into sheets.
• They often exhibit luster, giving them a shiny appearance.
• They vary in hardness and melting points, though many have moderately high melting points.
• Examples include pure metals like platinum ( Pt) and alloys.

The study of metallic solids is essential, as metals are crucial in countless applications, from construction and tools to electronics and vehicle manufacturing.