Gen Chem II

Learning Objectives

• Lesson 1.1 – Ionic Bonding

  • Depict main-group atoms using Lewis electron-dot structures

  • Depict the formation of ionic compounds with Lewis electron-dot structures

  • Describe how lattice energy is responsible for the formation of ionic compounds

  • Interpret periodic trends in lattice energies using Coulomb’s law

  • Rank relative lattice energies based on ionic properties

Chapter Overview: Models of Chemical Bonding

• Types of bonding models

  • Ionic bonding model

  • Covalent bonding model

  • Metallic bonding model

• Importance of tracking electrons for bonding analysis

Valence Electrons and Lewis Structures

• Only valence electrons are considered in bonding

• Use Lewis electron-dot structures for bookkeeping of valence electrons

Lewis Electron-Dot Symbols

• Method for main-group elements

  • Determine number of valence electrons

  • Place dots around element symbol until all are represented

Examples of Lewis Structures

• Show the Lewis structures for sodium (Na) and chlorine (Cl)

• Determine the number of electrons lost by sodium and gained by chlorine in the formation of NaCl

Gilbert Lewis and the Octet Rule

• Octet rule: Atoms gain, lose, or share electrons to obtain 8 electrons in the outer shell (2 for H and Li)

• Particularly applicable to Period 2 elements

Formation of Ionic Compounds

• Reaction example: Na(g) + Cl(g) → Na+(g) + Cl-(g)

• Discuss ionization energy (IE) and electron affinity (EA)

  • Prediction of reaction thermodynamics: Exothermic formation of NaCl observed

Lattice Energy

• Definition: Energy required to separate 1 mol of an ionic solid into gaseous ions

• Crystallization energy: Energy released when gaseous ions form an ionic solid

Factors Influencing Lattice Energy

• Comparison of ionic compounds

  • Size of ions and charges affects lattice energy

• Coulomb’s Law application: energy ∝ cation charge * anion charge / (cation radius + anion radius)

Properties of Ionic Compounds

• Characteristics: Hard, brittle solids; high melting and boiling points

• Conduct electricity when melted or dissolved in water

• Relationship between lattice energy and physical properties

  • Larger lattice energy → harder crystals, higher melting point, lower solubility in water

Summary of Key Takeaways

• Ability to draw Lewis structures and predict ionic bonding

• Understanding ionization energies and electron affinity

• Lattice energy's role in ionic compound formation and properties