Atomic, Ionic and Molecular Solids: Videos & Practice Problems

Solids are classified into crystalline and amorphous types. Crystalline solids, like ionic, molecular, covalent network, and metals, have ordered structures. Ionic solids, such as sodium chloride, are hard and brittle with high melting points. Molecular solids, like ice, are softer with lower melting points. Covalent network solids, exemplified by diamonds, are extremely hard. Metals exhibit metallic bonding, resulting in lustrous and variable hardness. Amorphous solids, like glass and tar, lack a defined structure and can flow, distinguishing them from crystalline forms.

Atomic, Ionic and Molecular Solids Concept 1

Solids can be fundamentally categorized into two main types: crystalline and amorphous solids. Crystalline solids are characterized by their highly ordered arrangements of atoms, ions, or molecules, while amorphous solids exhibit a random arrangement without any discernible pattern.

Crystalline solids can be further divided into four categories: ionic solids, molecular solids, covalent network solids, and metals. Ionic solids consist of cations and anions held together by electrostatic forces, which are the attractions between positively and negatively charged ions. These solids are typically hard and brittle, with high melting points. A common example is sodium chloride (NaCl).

Molecular solids, on the other hand, have molecules as their smallest units, and their intermolecular forces govern their properties. These solids tend to be softer and have low to moderate melting points, with ice (H₂O) serving as a classic example.

Covalent network solids are composed of atoms connected by covalent bonds, making them some of the hardest materials known. They possess very high melting points, often exceeding those of ionic solids. Diamonds, a form of carbon, exemplify covalent network solids due to their exceptional hardness.

Metals consist of metal atoms bonded through metallic bonds, which involve the delocalization of electrons. They can vary in texture from soft (like sodium) to hard (like titanium) and generally have high melting points. Examples include sodium and titanium.

In contrast, amorphous solids are made up of atoms, ions, molecules, or polymers, such as plastics. Due to their lack of a regular structure, they do not have a distinct melting point and can exhibit flow, a property typically associated with liquids. Common examples of amorphous solids include glass and tar, the latter being a sticky substance used in road construction.

Understanding these distinctions between crystalline and amorphous solids, along with their subcategories, is essential for grasping the diverse properties and behaviors of materials in various applications.

Atomic, Ionic and Molecular Solids Example 1

Ionic solids are compounds formed from the electrostatic attraction between positively charged ions (cations) and negatively charged ions (anions). Typically, the cations are metals or the ammonium ion, while the anions are nonmetals. In identifying an ionic solid, one must look for a combination of these ions.

For example, in the case of aluminum fluoride (AlF₃), aluminum acts as the cation, being a metal, and fluorine serves as the anion, being a nonmetal. This combination exemplifies the characteristics of an ionic compound, making aluminum fluoride a clear example of an ionic solid.

Thus, when evaluating options for ionic solids, it is essential to identify pairs of cations and anions that fit this ionic structure. In this scenario, option C, which includes aluminum and fluorine, is the correct identification of an ionic solid.

What is the major electrostatic force found within an ammonia molecule, NH₃? 

• A. Metallic bond
• B. Ionic bond
• C. Covalent bond
• D. Intermolecular Forces
• E. Anionic bond

Answer: (D)

As it cools off, olive oil slowly hardens and forms a solid over a range of temperatures. Which best describes it as a solid?

• A. Ionic
• B. Covalent Network
• C. Metallic
• D. Amorphous
• E. Molecular Crystals

Answer: (E)

Compound A is hard, doesn't conduct electricity, and melts at 1400ºC. Compound A represents which of the following:

• A. Ionic solid
• B. Metallic solid
• C. Molecular solid
• D. Covalent Network solid

Answer: (D)

Classify each solid as amorphous, molecular, network covalent, alloy or ionic.
a) Steel                                                    ______________________
b) CO₂                                                     ______________________
c) Graphite                                              ______________________
d) CaCO₃                                                 ______________________
e) Bronze, an alloy of Cu and Sn           ______________________

• A. alloy, molecular, network covalent, ionic, alloy
• B. alloy, molecular, molecular, ionic, ionic
• C. ionic, molecular, network covalent, ionic, alloy
• D. ionic, network covalent, molecular, alloy, ionic
• E. alloy, network covalent, molecular, alloy, ionic
• F. network covalent, molecular, molecular, alloy, ionic

Answer: (A)

Here’s what students ask on this topic:

What is the difference between crystalline and amorphous solids?

Crystalline solids have a highly ordered arrangement of atoms, ions, or molecules, forming a repeating pattern throughout the material. Examples include ionic solids like sodium chloride, molecular solids like ice, covalent network solids like diamonds, and metals. These solids typically have distinct melting points and well-defined physical properties. In contrast, amorphous solids lack a long-range order in their atomic or molecular arrangement. They do not have a repeating pattern and can flow under certain conditions, which is unusual for solids. Examples include glass and tar. Amorphous solids do not have a distinct melting point and exhibit a range of melting behaviors.

What are the properties of ionic solids?

Ionic solids are composed of positive and negative ions held together by strong electrostatic forces. These solids are typically hard and brittle, with high melting points due to the strong attraction between the ions. A common example of an ionic solid is sodium chloride (NaCl). Ionic solids also tend to be good insulators in their solid state but can conduct electricity when melted or dissolved in water, as the ions are free to move and carry charge in these states.

How do covalent network solids differ from molecular solids?

Covalent network solids consist of atoms connected by covalent bonds in a continuous network, resulting in extremely hard materials with very high melting points. Diamonds, a form of carbon, are a prime example. In contrast, molecular solids are composed of molecules held together by intermolecular forces, such as hydrogen bonds, dipole-dipole interactions, or van der Waals forces. These forces are weaker than covalent bonds, making molecular solids softer with lower melting points. Ice (solid H₂O) is an example of a molecular solid.

What are the characteristics of metallic solids?

Metallic solids are composed of metal atoms arranged in a lattice structure, held together by metallic bonds. These bonds involve a 'sea of electrons' that are free to move throughout the structure, giving metals their characteristic properties. Metallic solids are typically lustrous (shiny), malleable, and ductile. They can range from soft (like sodium) to very hard (like titanium). Metals also have high melting points and are excellent conductors of electricity and heat due to the mobility of their electrons.

Why do amorphous solids lack a distinct melting point?

Amorphous solids lack a long-range ordered structure, meaning their atoms, ions, or molecules are arranged randomly. This irregular arrangement causes them to soften over a range of temperatures rather than having a sharp melting point. As a result, amorphous solids transition gradually from a solid to a liquid state. Examples include glass and tar. The lack of a distinct melting point is a key characteristic that differentiates amorphous solids from crystalline solids, which have well-defined melting points due to their ordered structures.