Problem 14 - Introductory Chemistry Atoms First

Question

The following are solids at room temperature (about \(25^{\circ} \mathrm{C}\) ). Classify them as molecular, ionic, network, or metallic: (a) Zirconium, \(\mathrm{Zr}, \mathrm{mp}=1852{ }^{\circ} \mathrm{C}\) (b) Lead, \(\mathrm{Pb}, \mathrm{mp}=328^{\circ} \mathrm{C}\) (c) Calcium nitride, \(\mathrm{Ca}_{3} \mathrm{~N}_{2}, \mathrm{mp}=1195^{\circ} \mathrm{C}\) (d) Graphite form of carbon, \(\mathrm{C}\), sublimes at \(3652{ }^{\circ} \mathrm{C}\) (e) Yellow phosphorus, \(\mathrm{P}_{4}, \mathrm{mp}=44^{\circ} \mathrm{C}\)

Step-by-Step Solution

Answer

(a) Zirconium (Zr) is a metallic solid. (b) Lead (Pb) is a metallic solid. (c) Calcium Nitride (Ca3N2) is an ionic solid. (d) Graphite form of carbon (C) is a network solid. (e) Yellow Phosphorus (P4) is a molecular solid.

Step 1: (a) Classify Zirconium (Zr)

Zirconium (Zr) is a metal, so it will have metallic bonding. Thus, Zirconium will be classified as a metallic solid.

Step 2: (b) Classify Lead (Pb)

Lead (Pb) is also a metal and has metallic bonding. Therefore, Lead will be classified as a metallic solid.

Step 3: (c) Classify Calcium Nitride (Ca3N2)

Calcium Nitride (Ca3N2) is a compound formed by a metal (Calcium) and a non-metal (Nitrogen). It has ionic bonding between the metal (positive ions) and non-metal (negative ions). So, Calcium Nitride will be classified as an ionic solid.

Step 4: (d) Classify Graphite form of carbon (C)

Graphite is a form of carbon (C) which has covalent bonds (network covalent bonding) between the individual atoms, forming a vast network of interconnected carbon atoms. As a result, graphite will be classified as a network solid.

Step 5: (e) Classify Yellow Phosphorus (P4)

Yellow Phosphorus (P4) is a covalent compound with molecular (covalent) bonding between the individual P4 molecules. Since it has molecular bonds and is not part of a larger network or ionic structure, Yellow Phosphorus will be classified as a molecular solid. To summarize: (a) Zirconium (Zr) is a metallic solid. (b) Lead (Pb) is a metallic solid. (c) Calcium Nitride (Ca3N2) is an ionic solid. (d) Graphite form of carbon (C) is a network solid. (e) Yellow Phosphorus (P4) is a molecular solid.

Key Concepts

Metallic Solids

Metallic solids are a unique group of solids characterized by their metallic bonding. These solids are made up of closely packed metal atoms.
The electrons in metallic solids are not bound to any specific atom and move freely, creating what is known as a "sea of electrons."
This electron sea explains many properties of metals, such as their ability to conduct electricity and heat, as well as their malleability and ductility.

• Examples: Common metallic solids include zirconium (Zr) and lead (Pb).
• Structure: The atoms are arranged in a repeating pattern known as a lattice structure.
• Applications: Due to their strong mechanical properties, metallic solids are widely used in construction, manufacturing, and electronic applications.

Ionic Solids

Ionic solids are formed when metals transfer electrons to nonmetals, creating a bond between positive and negative ions. These bonds are very strong and hold the structure rigidly together.
Because their ions are held in a fixed position, ionic solids tend to be brittle.

• Examples: Calcium nitride (Ca₃N₂) is a perfect example of an ionic solid, made from the combination of calcium and nitrogen atoms.
• Structure: The ions are arranged in a crystal lattice structure, forming a high melting point solid due to the strong ionic bonds.
• Properties: They have high melting and boiling points and are generally soluble in water.

Network Covalent Solids

Network covalent solids are one large network of covalently bonded atoms. This type of bonding extends throughout the material, creating an extremely hard and durable solid.
Unlike other types of solids, network covalent solids do not consist of individual molecules.

• Examples: A well-known network covalent solid is graphite, a form of carbon.
• Structure: Atoms are interconnected in a continuous network, offering incredible stability and high melting points.
• Use Cases: These solids have unique properties like temperature resistance and strength, making them useful in various industrial applications.

Molecular Solids

Molecular solids are formed by molecules held together by intermolecular forces like hydrogen bonding, dipole-dipole interactions, or Van der Waals forces. These forces are weaker compared to ionic or covalent bonds.

• Examples: Yellow phosphorus (P₄) is an example of a molecular solid, where P₄ molecules are not interconnected by strong network bonds.
• Structure: Typically, these solids have lower melting and boiling points.
• Characteristics: They tend to be softer compared to other types of solids and are often insulators, making them less conductive of electricity and heat.