Question

Classify each of the following crystalline solids as ionic, molecular, or metallic: (a) \(2 \mathrm{inc}, Z \mathrm{n}\) (b) zinc oxide, \(Z \mathrm{nO}\) (c) phosphorus, \(P_{4}\) (d) iodine monobromide, IBr

Short answer

Zinc is metallic, ZnO is ionic, P₄ is molecular, and IBr is molecular.

Step-by-step solution

Identify the Type of Bond in Zinc (Zn)

Zinc (Zn) has metallic bonding. In metallic bonds, electrons are shared among a lattice of metal cations. These bonds give metals their characteristic properties like conductivity and malleability.

Determine the Nature of Zinc Oxide (ZnO)

Zinc oxide (ZnO) is an ionic compound. It forms from the transfer of electrons between zinc and oxygen atoms, resulting in positively charged zinc ions (Zn²⁺) and negatively charged oxide ions (O²⁻). This electron transfer results in ionic bonds.

Characterize Phosphorus (P₄)

Phosphorus (P₄) forms a molecular solid. Each phosphorus atom in the molecule is bound to others by covalent bonds, and these molecules are held together by weaker Van der Waals forces in the solid state.

Identify the Bonding in Iodine Monobromide (IBr)

Iodine monobromide (IBr) is a molecular solid, composed of molecules held together by covalent bonds. These molecules, in turn, are held together in the solid state by Van der Waals forces, making it a molecular solid.

Key concepts

Ionic Bonds

Ionic bonds form when electrons are transferred between atoms, leading to the creation of charged ions. Most commonly found between metals and nonmetals, these bonds result from the strong electrostatic attraction between oppositely charged ions. For instance, in zinc oxide (ZnO), zinc loses two electrons to become a positively charged ion \((Zn^{2+})\), while oxygen gains those electrons to become a negatively charged ion \((O^{2-})\). This transfer leads to the formation of a strong ionic bond.

Crystalline solids that are classified as ionic typically have high melting points and are excellent conductors of electricity in their molten state or when dissolved in water. This is because the movement of ions promotes conductivity. Ionic solids are also generally brittle due to the rigid structure formed by the regular arrangement of ions in their lattice.

Metallic Bonds

Metallic bonds are unique to metals and involve a sea of electrons that are shared among a lattice of metal cations. These electrons are free to move throughout the structure, which is why metals like zinc exhibit characteristics such as conductivity and malleability. In the case of zinc (Zn), the metal atoms are held together by these metallic bonds, resulting in a solid structure that can efficiently conduct heat and electricity.

This electron sharing gives metallic solids their ability to deform without breaking, which is often observed in materials like copper and aluminum. The ductility and malleability of metals make them ideal for various industrial applications. The strength of metallic bonds also contributes to the high melting points of these materials, although this can vary with the specific type of metal.

Molecular Solids

Molecular solids are composed of molecules held together by intermolecular forces, such as Van der Waals forces or hydrogen bonds. Unlike ionic or metallic bonds, these forces are generally weak, which is why molecular solids have lower melting and boiling points. Phosphorus \(P_4\) and iodine monobromide (IBr) are examples of molecular solids. In these substances, molecules are bound internally by covalent bonds, but are held together in the solid state by weaker interactions.

Although these solids are not good conductors of electricity, their applications range from pharmaceuticals to simple everyday materials like sugar and ice. The softness and malleability of molecular solids are directly attributable to the weak forces that govern their structure. This property makes them distinct from the more rigid structures seen in ionic and metallic crystalline solids.