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 varied hardness and high melting points. 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 structure is maintained by intermolecular forces. 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 attraction of electrons across the metal's surface. Metals can vary in texture from soft, like sodium, to hard, like titanium, and generally have high melting points.

In contrast, amorphous solids, which include materials like glass and tar, are composed of atoms, ions, or molecules arranged without a specific pattern. This lack of order results in amorphous solids not having a distinct melting point, and they can exhibit flow, a property typically associated with liquids. For instance, tar, used in road construction, is a black, sticky substance that can flow despite being classified as a solid.

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

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, the aluminum ion (Al³⁺) acts as the cation, and the fluoride ions (F^-) serve as the anions. This combination exemplifies the characteristics of an ionic compound, making aluminum fluoride a classic example of an ionic solid.

Thus, when evaluating options for ionic solids, the presence of a metal cation paired with nonmetal anions is key. In this scenario, option C, which includes aluminum and fluorine, correctly represents 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 highly ordered arrangements of atoms, ions, or molecules throughout their structure. Examples include ionic solids like sodium chloride, molecular solids like ice, covalent network solids like diamonds, and metals. These solids have distinct melting points and well-defined geometric shapes. In contrast, amorphous solids lack a defined structure and do not have a discernible pattern. Examples include glass and tar. Amorphous solids do not have a distinct melting point and can flow, which is unusual for solids. This difference in structure leads to varied physical properties between crystalline and amorphous solids.

What are the properties of ionic solids?

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

How do molecular solids differ from covalent network solids?

Molecular solids consist of molecules held together by intermolecular forces such as hydrogen bonds, dipole-dipole interactions, and London dispersion forces. These solids tend to be softer and have lower melting points compared to other types of solids. An example is ice (solid H₂O). In contrast, covalent network solids are composed of atoms connected by covalent bonds in a continuous network. These solids are extremely hard and have very high melting points. A prime example is diamond, which is a form of carbon. The strong covalent bonds in covalent network solids make them some of the hardest materials known.

What are the characteristics of metals as solids?

Metals as solids are composed of metal atoms held together by metallic bonds, which involve a 'sea' of delocalized electrons. This bonding gives metals their characteristic properties: they are typically lustrous (shiny), can range from soft (like sodium) to hard (like titanium), and have high melting points. Metals are also good conductors of electricity and heat due to the mobility of their electrons. The ability to deform without breaking (malleability) and to be drawn into wires (ductility) are also notable properties of metallic solids.

Why do amorphous solids lack a distinct melting point?

Amorphous solids lack a distinct melting point because their atoms, ions, or molecules are arranged randomly without a long-range order. This irregular structure means that different parts of the solid can have different bonding environments and strengths. As a result, amorphous solids soften over a range of temperatures rather than melting sharply at a specific temperature. Examples of amorphous solids include glass and tar. This lack of a defined structure also allows some amorphous solids to flow, which is atypical for solids.