Chapter 7: Covalent Bonds and Molecular Compounds

Unlike ionic compounds that involve complete electron transfer, covalent bonds form when atoms achieve stable electron configurations by sharing electron pairs, creating molecules such as water, carbon dioxide, and methane that are essential to biological and environmental systems. The chapter begins with Lewis structure construction, a critical skill requiring students to count valence electrons and correctly position bonding pairs and lone pairs around atoms to represent molecular geometry and electron distribution. Understanding bond order—including single, double, and triple bonds—enables students to predict molecular stability and reactivity based on the strength and length of these connections. The distinction between molecular formulas and structural formulas becomes clear through practice, as structural representations reveal the precise arrangement of atoms that molecular formulas alone cannot convey. Nomenclature of binary molecular compounds follows systematic rules using Greek prefixes to denote atom quantities, ensuring clarity in chemical communication. A central concept involves electronegativity and bond polarity, which explain how unequal electron sharing creates partial charges and molecular dipole moments that influence chemical behavior. The chapter introduces Valence Shell Electron Pair Repulsion theory as the predictive framework for determining three-dimensional molecular geometries including linear, bent, trigonal planar, and tetrahedral arrangements. These shapes directly impact physical properties such as boiling point, melting point, and solubility. The final sections address intermolecular forces—including dipole-dipole interactions, hydrogen bonding, and London dispersion forces—that govern how molecules interact in biological systems and determine bulk properties of substances. Together, these concepts provide students with the theoretical foundation and practical skills necessary to understand molecular behavior in health sciences, environmental chemistry, and organic synthesis.