Question

Indicate the type of crystal (molecular, metallic, covalent-network, or ionic) each of the following would form upon solidification: (a) \(\mathrm{CaCO}_{3},(\mathrm{~b}) \mathrm{Pt}\), (c) \(\mathrm{ZrO}_{2}\) (melting point, \(2677^{\circ} \mathrm{C}\) ), (d) table sugar \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\), (e) benzene, (f) \(I_{2}\).

Short answer

(a) CaCO3: Ionic solid (b) Pt: Metallic solid (c) ZrO2: Ionic solid (d) C12H22O11 (table sugar): Molecular solid (e) Benzene: Molecular solid (f) I2: Molecular solid

Step-by-step solution

Identify the components

In this step, identify the different elements and ions that constitute each compound. (a) CaCO3: calcium (Ca), carbonate ion (CO3^2-) (b) Pt: platinum (c) ZrO2: zirconium (Zr), oxide ion (O^2-) (d) C12H22O11: carbon (C), hydrogen (H), and oxygen (O) (e) Benzene: carbon (C), hydrogen (H) (f) I2: iodine (I)

Determine the type of bond

In this step, determine the type of bond(s) formed between the components of each compound. (a) CaCO3: Ionic (metal and polyatomic ion) (b) Pt: Metallic (single metal element) (c) ZrO2: Ionic (metal and non-metal ion) (d) C12H22O11: Covalent (non-metal elements) (e) Benzene: Covalent (non-metal elements) (f) I2: Covalent (single non-metal element)

Classify each compound as a type of solid

Now, based on the type of bond formed, classify each compound as a molecular, metallic, covalent-network, or ionic solid. (a) CaCO3: Ionic solid (b) Pt: Metallic solid (c) ZrO2: Ionic solid (high melting point indicates strong ionic bonding) (d) C12H22O11 (table sugar): Molecular solid (covalent bond, but not in extensive network structure) (e) Benzene: Molecular solid (covalent bond, but not in extensive network structure) (f) I2: Molecular solid (weak Van der Waals forces between the I2 molecules)

Key concepts

Ionic Bonds

Ionic bonds are the electrical forces that hold together ions in an ionic compound. When metals react with non-metals, electrons are typically transferred from the metal atoms to the nonmetal atoms. This process results in the formation of positive metal cations and negative non-metal anions. These oppositely charged ions attract, forming a strong ionic bond.
For example, calcium carbonate ( CaCO_3 ) forms an ionic bond. Calcium, a metal, donates electrons to the carbonate, a polyatomic non-metal ion. These ionic bonds give calcium carbonate its solid structure and relatively high melting point.

• Ionic bonds result in the creation of ionic solids, which are usually hard and brittle.
• They often dissolve well in water and conduct electricity in their molten state or when dissolved.

Taking zirconium dioxide ( ZrO_2 ) as another example, it's comprised of a metal (zirconium) and a non-metal (oxygen), demonstrating how such ionic binding can lead to high melting points.

Covalent Bonds

Covalent bonds are formed when two non-metal atoms share pairs of electrons. These shared electrons allow each atom to achieve a full outer electron shell, contributing to a stable electronic arrangement. Covalent bonds can involve single, double, or even triple sharing of electrons.
Molecules like table sugar ( C_{12}H_{22}O_{11} ) and benzene consist of atoms bonded covalently, forming molecular solids. Though these solids can form intricate molecular architectures, they do not create the extensive network structure akin to diamond or quartz.

• In molecular solids, covalent ties bind molecules inside the units, but intermolecular forces maintain the overall solid form.
• These solids usually have low melting points and might not conduct electricity well.

Iodine ( I_2 ) is another example of a molecular solid with covalent bonds within each diatomic molecule.

Metallic Bonds

Metallic bonds occur between metal atoms. In a metallic bond, electrons are not just transferred or shared between specific atoms. Instead, they form a 'sea of electrons' that are free to move between multiple atoms. This delocalization contributes to metals’ conductivity and malleability.
For instance, platinum ( Pt ) showcases metallic bonds. The atoms are closely packed together, and the free electrons allow for the conduction of electricity and heat.

• Metallic solids are generally shiny, conductive, and malleable.
• They form dense solid structures because of the tightly packed atom arrangement.

This explanation can be additionally applied to numerous metals found in various industrial and residential applications.

Molecular Solids

Molecular solids are formed by molecules bound together by Van der Waals forces, dipole-dipole interactions, or hydrogen bonds, rather than covalent or ionic forces. These intermolecular forces are weaker, generally resulting in lower melting and boiling points.
An example is benzene, which comprises covalently bonded carbon and hydrogen atoms. Though each individual molecule is strong, the forces between multiple benzene molecules are weak.

• Molecular solids often appear as gases or liquids at room temperature, due to weak interactions.
• They display varying degrees of solubility depending on the nature of the molecules and the solvent.

Table sugar ( C_{12}H_{22}O_{11} ) also illustrates a typical molecular solid, showing sweetness in numerous foods and drinks.

Classification of Solids

The classification of solids involves grouping them based on the types of bonds present and the overall structure they form. This classification helps in understanding the physical properties and behaviors of solid materials.
Here are the main categories:

• Ionic Solids: Composed of ions held together by ionic bonds. Example: CaCO_3 (Calcium Carbonate).
• Molecular Solids: Molecules held together by intermolecular forces, like Van der Waals. Example: Iodine ( I_2 ), Benzene, and Table Sugar.
• Metallic Solids: Metal atoms held together by metallic bonds, characterized by delocalized electrons. Example: Platinum ( Pt ).
• Covalent-Network Solids: Atoms connected by an extensive network of covalent bonds, leading to high melting points. Note: None from the given examples.

These classifications are paramount in material science, allowing predictions and adjustments of properties for practical applications in engineering and technology.