Chapter 10: Liquids & Solids: Intermolecular Forces and States of Matter

Intermolecular forces, including London dispersion forces, dipole-dipole interactions, and hydrogen bonding, are presented as the primary determinants of physical properties such as boiling points, melting points, surface tension, and viscosity. Understanding these forces explains phenomena like water's anomalously high boiling point and the unusual density relationship between ice and liquid water. The liquid state is characterized by how intermolecular attractions permit molecular flow while maintaining a fixed volume, with detailed examination of properties including viscosity, capillary action, and surface tension. The solid state is then classified into crystalline and amorphous categories, with emphasis on how crystalline solids possess repeating three-dimensional patterns defined by unit cells. Simple cubic, body-centered cubic, and face-centered cubic structures are analyzed for their geometric arrangements and coordination numbers, which directly influence material density and packing efficiency. Metallic solids are explained through the electron-sea model and band theory, accounting for electrical conductivity, malleability, and the diversity of metallic properties. Network atomic solids such as diamond, graphite, and silicon demonstrate how atomic connectivity determines hardness and electrical behavior, while the technological significance of graphene is highlighted. Molecular solids and ionic solids are contrasted through structural examples and their property relationships. Polymorphism—the ability of substances to exist in multiple crystalline forms—is illustrated through carbon allotropes and silicon-based materials. The chapter concludes by exploring phase changes and phase diagrams, which map the conditions of temperature and pressure governing the stability of each state. Vapor pressure, boiling, sublimation, fusion, and critical points are connected to heating curves and phase diagrams for representative substances like water and carbon dioxide, enabling students to predict phase behavior under varying conditions.