Question

What kinds of attractive forces exist between particles in (a) molecular crystals, (b) covalent-network crystals, (c) ionic crystals, (d) metallic crystals?

Short answer

(a) In molecular crystals, weak intermolecular forces like dispersion forces, dipole-dipole interactions, and hydrogen bonding exist between particles. (b) In covalent-network crystals, strong and directional covalent bonds are the attractive forces between particles. (c) Ionic crystals have ionic bonds, which are strong electrostatic attractions between cations and anions. (d) Metallic crystals have metallic bonds, arising from electrostatic attraction between positive metal ions and delocalized electrons.

Step-by-step solution

(a) Molecular Crystals

Molecular crystals are made up of molecules held together by weak intermolecular forces. There are three main types of intermolecular forces: dispersion forces (also known as London forces), dipole-dipole interactions, and hydrogen bonding. The type of intermolecular force that exists between the particles depends on the specific molecules present in the crystal.

(b) Covalent-Network Crystals

Covalent-network crystals consist of atoms covalently bonded together in an extended network. The attractive forces between particles in a covalent-network crystal are the covalent bonds themselves, which are strong and directional in nature. These covalent bonds result in a stable and rigid crystal structure. Well-known examples include diamond, graphite, and silicon dioxide (SiO2).

(c) Ionic Crystals

Ionic crystals are made up of cations and anions held together by strong electrostatic attractions known as ionic bonds. The positive and negative charges of the ions cause them to attract one another, leading to the formation of a regular, repeating crystal lattice. Examples of ionic crystals include common salts such as sodium chloride (NaCl) and potassium chloride (KCl).

(d) Metallic Crystals

Metallic crystals consist of metal atoms surrounded by a "sea" of delocalized electrons, which are free to move throughout the crystal lattice. The attractive forces between particles in a metallic crystal are the metallic bonds, which are a result of the electrostatic attraction between the positive metal ions (cations) and the delocalized electrons. This bonding results in properties such as electrical and thermal conductivity, as well as the malleability and ductility of metals.