Question

On the basis of the description given, classify each of these solids as molecular, metallic, ionic, network, or amorphous, and explain your reasoning. (a) A soft, slippery solid that has no definite melting point but decomposes at temperatures above \(250{ }^{\circ} \mathrm{C} ;\) the solid does not conduct electricity (b) Violet crystals that melt at \(114{ }^{\circ} \mathrm{C}\) and whose vapor irritates the nose; neither the solid nor the liquid conducts electricity (c) Hard, colorless crystals that melt at \(2800^{\circ} \mathrm{C} ;\) the liquid conducts electricity, but the solid does not (d) A hard solid that melts at \(3410^{\circ} \mathrm{C}\); both the solid and the liquid conduct electricity

Short answer

(a) Amorphous; (b) Molecular; (c) Ionic; (d) Metallic.

Step-by-step solution

Analyze Solid (a) Properties

Solid (a) is described as soft, slippery with no definite melting point and decomposition at high temperature. It does not conduct electricity. These characteristics are typical of amorphous solids, which have irregular arrangements of atoms and lack a sharp melting point.

Analyze Solid (b) Properties

Solid (b) is described as violet crystals that melt at 114\(^{\circ}\)C with vapors that irritate the nose. Neither the solid nor the liquid conducts electricity. These features are indicative of a molecular solid, like iodine, which consists of discrete molecules held together by weak van der Waals forces.

Analyze Solid (c) Properties

Solid (c) consists of hard, colorless crystals with high melting points, and its liquid state conducts electricity, while the solid does not. These characteristics are typical of ionic solids, which have ions arranged in a crystal lattice and whose liquid state allows for ion mobility and electrical conductivity.

Analyze Solid (d) Properties

Solid (d) is described as hard and melts at a very high temperature of 3410\(^{\circ}\)C. Both the solid and the liquid conduct electricity. These features are typical of metallic solids, where metal atoms share a "sea of electrons," allowing for conductivity in both states.

Key concepts

Amorphous Solids

Amorphous solids are materials in which atoms or molecules do not have a long-range ordered structure. Unlike crystalline solids, where the components are arranged in a regular pattern, amorphous solids resemble the disorganized state of liquids but retain a solid form. This lack of order results in several key properties. Most notably, amorphous solids do not have a sharp melting point. Instead, they soften over a range of temperatures. This softening is because there's no defined structure that breaks at one specific temperature. Additionally, because their molecules are not arranged systematically, amorphous solids generally do not conduct electricity. Common examples include glass, gels, and some plastics.

Molecular Solids

Molecular solids are composed of discrete molecules held together by relatively weak forces, such as van der Waals forces, hydrogen bonds, or dipole-dipole interactions. These forces are significantly weaker than the ionic or covalent bonds found in other types of solids, which leads to distinctive properties. Molecular solids generally have low melting points because only the weak intermolecular forces need to be overcome for the solid to melt. These solids are often soft and, because they lack free ions or electrons, they typically do not conduct electricity. Examples include solid forms of gases like oxygen and nitrogen at low temperatures, and more familiar substances like sugar and dry ice.

Ionic Solids

Ionic solids consist of positively and negatively charged ions held together by strong electrostatic forces known as ionic bonds. This results in a regular crystalline structure, often resulting in hard and brittle materials with high melting points. The high melting point of ionic solids is due to the significant energy required to overcome the strong ionic bonds between the ions. In their solid state, ionic solids do not conduct electricity because their charged particles are fixed in place. However, when melted or dissolved in water, the ions become free to move, allowing ionic solids to conduct electricity in their liquid state. Common examples include sodium chloride (table salt) and calcium fluoride.

Metallic Solids

Metallic solids are characterized by their unique structure of metal atoms surrounded by a "sea of electrons." These delocalized electrons are not bound to any specific atom and can move freely throughout the solid. This electron mobility is responsible for many characteristics of metallic solids. They are typically good conductors of electricity and heat because the electrons can carry energy efficiently. Metallic solids are also known for their malleability and ductility, meaning they can be hammered into sheets or drawn into wires without breaking. This is because the metal atoms can slide past one another easily due to the electron sea. Metals like copper, aluminum, and iron are typical examples of metallic solids, used extensively in industries due to these versatile properties.