Question

What is a network solid? Give an example of a network solid and describe the bonding in such a solid. How does a network solid differ from a molecular solid?

Short answer

A network solid is a crystalline material composed of atoms connected by strong covalent bonds in a continuous three-dimensional arrangement, resulting in high melting and boiling points, high hardness, and low electrical conductivity. An example of a network solid is diamond, where carbon atoms are covalently bonded in a rigid lattice structure. Molecular solids, on the other hand, consist of discrete molecules held together by weaker intermolecular forces, leading to low melting and boiling points, low hardness, and low electrical conductivity. The primary difference between network solids and molecular solids lies in the type of bonding and overall structure: strong covalent bonds in a continuous lattice for network solids versus weak intermolecular forces in a discrete arrangement for molecular solids.

Step-by-step solution

1. Definition of a Network Solid

A network solid, also known as a covalent network solid or atomic solid, is a type of crystalline material made up of atoms linked together by strong covalent bonds in a continuous, three-dimensional arrangement. These strong bonds lead to its high melting and boiling points, and usually, high hardness and low electrical conductivity.

2. Example of a Network Solid

One common example of a network solid is diamond, which is an allotrope of carbon. In diamond, each carbon atom is connected to four other carbon atoms via strong covalent bonds, resulting in a stable and rigid lattice structure.

3. Bonding in Network Solids

As mentioned earlier, network solids consist of atoms held together by covalent bonds. These bonds involve the sharing of a pair of electrons between two atoms, which results in a strong and stable bond due to the attraction between the positively charged nuclei and the negatively charged shared electrons. These strong covalent bonds are highly directional, which means they are oriented in specific directions in the lattice, contributing to the overall rigidity and stability of the structure.

4. Definition of a Molecular Solid

A molecular solid is a crystalline material made up of discrete molecules held together by intermolecular forces such as hydrogen bonding, dipole-dipole interactions, or London dispersion forces. Molecular solids typically have low melting and boiling points, low hardness, and low electrical conductivity because the forces holding the molecules together are comparatively weak.

5. Differences Between Network Solids and Molecular Solids

The main differences between network solids and molecular solids arise from the types of bonding and forces present in each: a. Network solids consist of atoms bonded together by strong covalent bonds, whereas molecular solids are made up of discrete molecules held together by weaker intermolecular forces. b. Due to the strong covalent bonds, network solids generally have high melting and boiling points, high hardness, and low electrical conductivity. On the other hand, molecular solids exhibit low melting and boiling points, low hardness, and low electrical conductivity due to the weaker intermolecular forces. c. Network solids form continuous three-dimensional structures, while molecular solids have a more discrete arrangement with individual molecules separated by empty space. In summary, network solids are characterized by strong covalent bonds and continuous three-dimensional structures, while molecular solids are composed of discrete molecules held together by weak intermolecular forces.

Key concepts

Covalent Bonds

At the heart of network solids lies the concept of covalent bonds. These powerful connections between atoms are formed when pairs of electrons are shared. Each bond consists of a pair of electrons originating from each of the two bonded atoms, creating a strong mutual attraction that anchors the atoms together.

Picture each covalent bond as a rope tying two climbers together; no matter the tensions and stresses, the climbers remain anchored to one another. This is analogous to how atoms within a network solid are tightly held in a rigid, enduring structure. This strong and localized bond gives network solids their characteristic high melting points, remarkable hardness, and generally, makes them poor conductors of electricity due to lack of free-moving electrons.

Understanding covalent bonds in network solids is crucial because they define the material’s intrinsic properties and are why substances like diamond are so incredibly tough and durable.

Crystalline Materials

Network solids belong to a broader class known as crystalline materials, distinguished by their ordered, repeating three-dimensional arrangements of atoms. These patterns, or crystal lattices, extend throughout the entire material, giving rise to its uniformity and symmetry. Imagine a dance troupe moving in perfect cohesion, with each dancer (atom) occupying a precise position in relation to the others, forming an elegant and structured ensemble.

Crystalline structures are not exclusive to network solids; however, other types of crystals include ionic crystals, metallic crystals, and molecular crystals, each held together by different forces and bonds. The unique aspect of network solids within the crystalline family is the continuity of their covalent bonding, which prevents them from being easily parted or decomposed into smaller units.

The understanding of crystalline materials provides insight into the macroscopic properties such as the angles at which they cleave, their interaction with light, and their general stability under various conditions.

Intermolecular Forces

Intermolecular forces, the weaker ties between molecules, are the glue that holds molecular solids together. These forces can be like gentle handshakes between neighboring molecules – significant enough to maintain a structure, but far less strong than the covalent bonds within network solids.

Types of Intermolecular Forces

• Van der Waals Forces: They include London dispersion forces, present in all molecules but more prominent in non-polar molecules, and dipole-dipole interactions, which occur between polar molecules.
• Hydrogen Bonds: A special type of dipole-dipole interaction that happens when hydrogen is bound to a highly electronegative atom like oxygen or nitrogen.

These forces dictate a molecular solid’s physical properties such as lower melting and boiling points, because less energy is required to overcome these weaker interactions.

Crucially, this differentiation in bonding types between network solids (strong covalent bonds) and molecular solids (weaker intermolecular forces) is key to understanding their vastly different physical characteristics, as well as their applications in various industries from electronics to pharmaceuticals.