Question

Identify each solid as molecular, ionic, or atomic. (a) \(\mathrm{CaCl}_{2}(s)\) (b) \(\mathrm{CO}_{2}(s)\) (c) \(\mathrm{Ni}(\mathrm{s})\) (d) \(\mathrm{I}_{2}(s)\)

Short answer

(a) CaCl2 is an ionic solid. (b) CO2 is a molecular solid. (c) Ni is an atomic solid. (d) I2 is a molecular solid.

Step-by-step solution

- Identify the Type of Bonding in CaCl2

Examine the components in calcium chloride (CaCl2). Calcium (Ca) is a metal, and chlorine (Cl) is a nonmetal. The compound is formed by the transfer of electrons from the metal to the nonmetal, thereby forming an ionic bond. Thus, CaCl2 is considered an ionic solid.

- Identify the Type of Bonding in CO2

Look at the components in carbon dioxide (CO2). Carbon (C) and oxygen (O) are both nonmetals. They share electrons when they bond, creating a molecular compound. As a result, CO2 is a molecular solid.

- Classify the Solid State of Nickel (Ni)

Nickel (Ni) is an element and is a metal. Pure elements in the solid state that are metals are considered to be atomic solids. Nickel atoms are held together by metallic bonds. Therefore, solid nickel is an atomic solid.

- Determine the Bonding in I2

Iodine (I2) is a diatomic molecule made up of two iodine atoms. Since both are nonmetals, they are held together by covalent bonds forming a molecular solid. Hence, solid iodine is categorized as a molecular solid.

Key concepts

Ionic Solid

An ionic solid is a type of solid compound where the individual components are held together by ionic bonds. These bonds are formed between atoms with significantly different electronegativities, resulting in an electron transfer from one atom to another. The result is a structure consisting of positively charged ions, known as cations, and negatively charged ions, known as anions.

For example, calcium chloride ((CaCl_{2})) is a classic ionic solid. In this compound, calcium gives up electrons to chlorine, creating a lattice of Ca^2+ and Cl^- ions. Ionic solids are characterized by high melting and boiling points due to the strong forces of attraction between the oppositely charged ions. They typically dissolve in water and conduct electricity when molten or in solution, making them crucial in various applications, from table salt to batteries.

Molecular Solid

Molecular solids are materials where the constituent particles are molecules held together by relatively weak intermolecular forces, like van der Waals forces or hydrogen bonds. Unlike ionic or atomic solids, molecular solids are composed of neutral entities—they do not have ions.

Carbon dioxide ((CO_{2})), in its solid state known as dry ice, is a prime example of a molecular solid. Here, the molecules are held together in a lattice by weak intermolecular forces, contributing to its relatively low melting point. Molecular solids are often soft, have low to moderate melting points, and are poor conductors of heat and electricity. They are common in organic compounds and can be found in everything from plastic to pharmaceuticals.

Atomic Solid

Atomic solids are a class of solid materials where atoms are bonded together in a network. These bonds can be either metallic, covalent, or of the Van der Waals type, depending on the elements involved.

Nickel ((Ni)) serves as a typical example of a metallic atomic solid, where metal atoms share a 'sea' of delocalized electrons that binds them together. This type of bonding allows for malleable solids with good electrical and thermal conductivity and luster. On the other hand, diamond is a covalent atomic solid, where atoms are bonded by strong covalent bonds in a rigid structure, resulting in an extremely hard substance. Atomic solids have diverse properties, which are exploited in applications from jewelry to electronics.

Chemical Bonding

Chemical bonding is fundamental to the structure and properties of all solid materials. It refers to the attraction between atoms or ions that holds them together in a compound.

There are several primary types of chemical bonding. Ionic bonding occurs in ionic solids like (CaCl_{2}) and involves the transfer of electrons. Covalent bonding, present in molecular solids like (I_{2}) and covalent atomic solids like diamond, involves the sharing of electrons. Metallic bonding, specific to metals and metallic atomic solids like nickel ((Ni)), involves a 'sea' of delocalized electrons. The type of bonding dictates the properties of the material, such as hardness, melting point, electrical conductivity, and solubility.

Solid State Chemistry

Solid state chemistry encompasses the study of the synthesis, structure, and properties of solid phase materials. It plays a crucial role in understanding how atoms or molecules interact to form solids, whether they be ionic, molecular, or atomic.

One of the central concepts in solid state chemistry is crystal structure, which refers to the orderly geometric spatial arrangement of atoms or molecules in a solid. It dictates many of the physical properties of the material, from melting points to electrical conductivity. Solid state chemistry also deals with imperfections in solids, such as vacancies or interstitial defects, which can influence material properties. By mastering solid state chemistry, one can tailor materials for specific applications, leading to advancements in fields like electronics, renewable energy, and materials science.