AP Chemistry Unit 2: Molecular and Ionic Compounds and Their Properties

Overview

• Unit 2 covers the interaction of atoms to form various types of chemical bonds.
• Main focus is on different types of bonds: ionic bonds, covalent bonds, and metallic bonds.
• Also covers molecular structure, VSEPR model, Lewis Dot Diagrams, hybridization, etc.

Chemical Bonds

• Definition: Chemical bonds hold atoms together, making them act as a unit.
• Example: Water (H2O) consists of 2 hydrogen atoms and 1 oxygen atom bonded together.
• Bonds affect the physical properties of substances (e.g., graphite vs. diamond).
• Chemical reactions involve breaking and forming of bonds.

Types of Chemical Bonds

1. Ionic Bonds

• Form between metals and non-metals.
• Involve transfer of electrons, resulting in cations (+) and anions (-).
• Example: NaCl (sodium chloride).
• Characteristics:
  • High melting and boiling points; solid at room temperature.
  • Poor electrical conductivity in solid state; conducts electricity in liquid state.
  • Form crystal lattice structures.

2. Covalent Bonds

• Form when two atoms share electrons.
• Nonpolar Covalent Bonds: Electrons shared equally.
• Polar Covalent Bonds: Electrons shared unequally, leading to partial charges.
• Molecule polarity determined by bond polarity and molecular geometry.

3. Metallic Bonds

• Form between metallic cations and delocalized electrons.
• Metals are malleable, ductile, and good conductors due to free-moving electrons.
• Example: Alloys (mixtures of metals) like bronze.

Physical Properties of Ionic Compounds

• Rigidity: Due to strong ionic bonds.
• Brittleness: Due to repulsion when similar charges align.
• Conductivity: Depends on the state (solid vs. liquid/aqueous).

Coulomb's Law

• Describes the force between two charged particles.
• Strength of ionic bonds depends on charges of ions and distance between them.

Covalent Bond Characteristics

• Bond Length: Distance at which potential energy is minimized.
• Bond Strength: Increases with number of shared electrons (single < double < triple bond).
• Resonance Structures: Occur when multiple valid Lewis structures exist for a molecule.

VSEPR Theory (Valence Shell Electron Pair Repulsion)

• Determines molecular geometry based on minimizing repulsion between electron pairs.
• Common Geometries:
  • Linear
  • Bent
  • Trigonal Planar
  • Tetrahedral
  • Trigonal Bipyramidal
  • Octahedral

Hybridization

• Mixing of atomic orbitals to form new hybrid orbitals.
• Types:
  • SP
  • SP2
  • SP3
• Determined by the number of electron pairs around a central atom.

Lewis Dot Diagrams

• Show how atoms are bonded within a molecule.
• Follow the octet rule for valence electron arrangements.
• Formal charge calculations can help determine the most appropriate structure.

Polar vs. Nonpolar Molecules

• Determined by molecular geometry and bond polarity.
• Symmetrical geometries with equal bond polarities are nonpolar.

Summary

• Understanding bonding helps explain the properties and behaviors of substances.
• Mastery of these concepts is crucial for predicting outcomes in chemical reactions and identifying molecular structures.