Problem 80 - General Chemistry

Question

On the basis of the description given, classify each of the following solids as molecular, metallic, ionic, or covalent network. Explain your answers. a. a lustrous, yellow solid that conducts electricity b. a hard, black solid melting at \(2350^{\circ} \mathrm{C}\) to give a nonconducting liquid C. a nonconducting, pink solid melting at \(650^{\circ} \mathrm{C}\) to give an electrically conducting liquid d. red crystals having a characteristic odor and melting at \(171^{\circ} \mathrm{C}\)

Step-by-Step Solution

Answer

a. Metallic, b. Covalent Network, c. Ionic, d. Molecular.

Step 1: Identify Characteristics of Solid 'a'

Solid 'a' is characterized as a lustrous, yellow solid that conducts electricity. Lustrous appearance and the ability to conduct electricity typically indicate the presence of metallic bonds. Therefore, this solid is likely metallic.

Step 2: Analyze Characteristics of Solid 'b'

Solid 'b' is described as a hard, black solid that melts at a very high temperature of \(2350^{\circ} \mathrm{C}\). Upon melting, it becomes a nonconducting liquid. The high melting point, hardness, and inability to conduct electricity when molten suggest that it is a covalent network solid.

Step 3: Examine Properties of Solid 'c'

Solid 'c' is a nonconducting, pink solid that melts into a liquid which conducts electricity at \(650^{\circ} \mathrm{C}\). This is typical of ionic solids, where the solid state does not conduct electricity, but the molten state or aqueous solution does due to the mobility of ions.

Step 4: Interpret Features of Solid 'd'

Solid 'd' consists of red crystals with a characteristic odor and a relatively low melting point of \(171^{\circ} \mathrm{C}\). These traits are indicative of molecular solids, where individual molecules are held together by weaker forces such as Van der Waals forces or hydrogen bonds.

Key Concepts

Metallic Bonds

In the realm of solid state chemistry, metallic bonds play a significant role. These bonds occur when electrons are shared over many nuclei and move freely among atoms, which is why metallic solids are excellent conductors of electricity. You can imagine a 'sea of electrons' surrounding positively charged metal ions.
Some key attributes of metallic bonds include:

• Lustrous appearance due to the way they interact with light.
• Good electrical and thermal conductivity thanks to their delocalized electrons.
• Malleability and ductility, allowing metals to be shaped without breaking.
• Variable melting points, generally high, but can vary widely.

These characteristics explain why a lustrous solid like gold, silver, or copper conducts electricity, serving as a classic example of metallic bonding at work.

Ionic Solids

Ionic solids are fascinating structures formed when metals transfer electrons to nonmetals, creating ions that bond through electrostatic attraction. This formation results in a crystalline lattice that constitutes the solid.
Some classic traits of ionic solids include:

• High melting and boiling points due to strong ionic interactions.
• Hard and brittle nature, meaning they tend to shatter rather than bend.
• They don't conduct electricity as solids, but in their molten state or in solution, they do, due to ion mobility.

The nonconducting nature of these solids at room temperature contrasts with their conductive nature when melted, which is pivotal in applications like salt melting into a conducting liquid upon heating.

Covalent Network Solids

Covalent network solids are distinctive for their extensive network of covalent bonds. This interlocking of atoms extends throughout the solid, making it incredibly strong and stable.
Here's what you need to notice about covalent network solids:

• Exceptionally high melting points because breaking them requires overcoming strong covalent bonds.
• Usually hard and durable, characteristic of materials like diamond and quartz.
• Nonconducting when they're solids and liquids, since there is no electron or ion mobility.

A black solid that melts at a high temperature yet remains nonconductive in its liquid form is a prime example of a covalent network solid, reflecting its toughness and bonding strength.

Molecular Solids

Molecular solids are built from individual molecules held together by weaker intermolecular forces like Van der Waals forces or hydrogen bonds. They don't involve extensive bonding networks or free-floating electrons.
Here's what sets molecular solids apart:

• Lower melting and boiling points compared to other solids because intermolecular forces are weaker.
• Typically soft and may have a distinct odor.
• Poor conductors of electricity owing to the lack of charged particles or free electrons.

The presence of characteristic odors and relatively low melting points in substances like naphthalene or iodine defines their nature as molecular solids, making them distinct and easy to categorize within their group.