Question

State whether the following list of properties is most descriptive of an ionic, a molecular, or a metallic solid: (a) malleable, ductile, insoluble in water (b) high melting point, conductor of electricity when melted (c) low melting point, nonconductor of electrical current

Short answer

(a) Metallic solid; (b) Ionic solid; (c) Molecular solid.

Step-by-step solution

Identify Properties of Ionic Solids

Ionic solids are usually characterized by high melting points and the ability to conduct electricity when they are melted or dissolved in water. They tend to be brittle and dissolve in water to some extent.

Identify Properties of Molecular Solids

Molecular solids typically have low melting points and are poor conductors of electricity. They consist of molecules held together by weak intermolecular forces.

Identify Properties of Metallic Solids

Metallic solids are characterized by properties like malleability, ductility, and insolubility in water. They have a 'sea of electrons' allowing them to conduct electricity in both solid and molten states.

Assign Properties to Solids - Part (a)

The given properties: malleable, ductile, and insoluble in water, best describe a metallic solid. This aligns with metallic solids' inherent characteristics.

Assign Properties to Solids - Part (b)

For high melting point and conductor of electricity when melted, these properties suggest an ionic solid. Ionic compounds conduct electricity when melted due to the free movement of ions.

Assign Properties to Solids - Part (c)

The properties of a low melting point and nonconductor of electrical current match those of molecular solids, which do not conduct electricity as their electrons are not free to move.

Key concepts

Ionic Solids

Ionic solids are fascinating structures formed by the strong attraction between positively and negatively charged ions. These electrostatic forces create a highly ordered, repeating pattern known as a crystal lattice.
This lattice structure is responsible for the typical high melting points of ionic solids, as a large amount of energy is required to break these powerful bonds. When solid, they are poor conductors of electricity because the ions are locked in place and cannot move freely.
However, once dissolved in water or melted, the ions are liberated and can move, enabling the material to conduct electricity effectively. Examples of ionic solids include common table salt (NaCl) and calcium fluoride (CaF extsubscript{2}).
Easily recognizable attributes of ionic solids include:

• High melting and boiling points.
• Conductivity as melted or in solution.
• Generally hard and brittle.
• Solubility in polar solvents like water.

Molecular Solids

Molecular solids consist of discrete molecules held together by weak forces such as Van der Waals forces or hydrogen bonds. Due to these weak interactions, molecular solids have relatively low melting and boiling points compared to ionic or metallic solids.
These solids are usually soft and are poor conductors of electricity in all states because they do not contain free-moving charged particles. This is due to the fact that their electrons are fixed in covalent bonds within the molecules and can't flow freely.
Many organic compounds, like ice (frozen water) or dry ice (solid CO extsubscript{2}), are classic examples of molecular solids.
Key points about molecular solids include:

• Low melting and boiling points.
• Generally soft or brittle.
• Nonconductive of electricity.
• Often soluble in organic solvents but less so in water.

Metallic Solids

Metallic solids are unique due to their "sea of electrons," which are free to move throughout the solid. This property is a result of the delocalization of electrons, allowing metals to conduct electricity efficiently in both solid and molten states.
Unlike ionic and molecular solids, metallic solids are malleable and ductile, meaning they can be hammered into sheets or drawn into wires without breaking.
A particularly notable feature of metallic solids is their shiny, lustrous appearance, a result of light interacting with the electron cloud. Metals like copper, aluminum, and gold exemplify these properties.
Important characteristics of metallic solids include:

• High electrical and thermal conductivity.
• Insolubility in most solvents.
• Malleability and ductility.
• High melting and boiling points, although not as extreme as ionic solids.