Chemical Bonding Lecture Notes

Introduction

• Presented by Chris Harris from Allo Chemistry
• Focuses on CIE (Cambridge International Examination) Topic 3: Chemical Bonding.
• Covers different types of bonds:
  • Ionic
  • Covalent
  • Metallic
  • Hybridization and orbitals
• PowerPoint slides available for purchase for revision.

Importance of Bonding

• Fundamental to chemistry; explains how atoms and ions form molecules.

Ionic Bonding

Basics

• Ionic bonding involves oppositely charged ions held together by electrostatic attraction.
• Example: Sodium (Na) and Chlorine (Cl)
  • Na: 1 electron in outer shell (Group 1)
  • Cl: 7 electrons in outer shell (Group 7)
  • Na loses an electron, forming Na⁺; Cl gains an electron, forming Cl⁻.

Dot Cross Diagrams

• Used to illustrate ionic bonding.
• Show outer shell electrons in bonding.

Common Ions

• Familiarize with common ions from groups 1, 2, 3, 5, 6, and 7.
• Examples of molecular ions:
  • Hydroxide (OH⁻)
  • Nitrate (NO₃⁻)
  • Ammonium (NH₄⁺)
  • Sulfate (SO₄²⁻)
  • Carbonate (CO₃²⁻)

Formula Calculation

• Swap and Drop Method
  • Write out the charges and ions.
  • Swap the charges and drop them as subscripts.
  • Example:
    • Calcium (Ca²⁺) and Nitrate (NO₃⁻) → Ca(NO₃)₂
    • Calcium (Ca²⁺) and Oxygen (O²⁻) → CaO

Ionic Structures

• Sodium chloride (NaCl) as a giant ionic structure.
• Cube-shaped with a regular pattern of ions.
• Properties:
  • High melting points due to strong attractions
  • Soluble in water; conducts electricity when molten or dissolved
  • Brittle; layers of ions can slide over each other, causing breaks

Electrolysis Demonstration

• Example using copper(II) chromate on wet filter paper to demonstrate charged particles in ionic substances.

Covalent Bonding

Basics

• Covalent bonds involve sharing of outer electrons, typically between non-metals.
• Types of covalent bonds:
  • Single, double, and triple bonds (number of shared electrons).
• Dative covalent (coordinate) bonds: one atom donates both electrons.

Examples

• Ammonia (NH₃), Carbon monoxide (CO), and Aluminium chloride (AlCl₃).

Bond Strength and Length

• Shorter bonds have higher bond enthalpy.
• Bond length is influenced by attractive and repulsive forces between nuclei and shared electrons.

Molecular Shapes

• Shapes determined by bond pairs and lone pairs of electrons.
• Examples:
  • Ammonia (NH₃): Pyramidal, bond angle 107°
  • Water (H₂O): Bent, bond angle 104.5°
  • Methane (CH₄): Tetrahedral, bond angle 109.5°

Giant Covalent Structures

Examples

• Graphite:
  • High melting point, conducts electricity, layers can slide.
• Diamond:
  • Extremely hard, high melting point, does not conduct electricity.
• Silicon Dioxide (SiO₂): Similar properties to diamond.

Hybridization

• Orbitals overlap to form bonds (sigma and pi bonds).
• Hybridization forms new orbitals (e.g., SP3 from carbon).
• SP2 and SP hybridization for double and triple bonds, respectively.

Electronegativity

• Ability of an atom to attract electrons in a bond.
• Increases across a period and decreases down a group.
• Fluorine is the most electronegative element (value of 4).

Polar vs Non-polar Bonds

• Polar bonds: Unequal sharing of electrons due to differences in electronegativity (e.g., HCl).
• Non-polar bonds: Equal sharing of electrons (e.g., hydrocarbons).

Intermolecular Forces

Types

1. Van der Waals Forces: Weak, temporary dipoles.
2. Permanent Dipole-Dipole Forces: Exist in polar molecules (e.g., HCl, water).
3. Hydrogen Bonding: Strongest intermolecular force; occurs with H and F, O, or N.

Properties

• Polar molecules dissolve well in polar solvents (e.g., water).
• Non-polar molecules do not dissolve in polar solvents.

Metallic Bonding

Basics

• Occurs between metal atoms; forms giant metallic structures.
• Involves a sea of delocalized electrons.

Properties

• High melting points, good conductors of heat and electricity, malleable, and ductile.

Summary

• Four main types of bonding: Giant Covalent, Simple Molecular Covalent, Ionic, and Metallic.
• Understand hybridization, electronegativity, and intermolecular forces.
• Important to practice and familiarize yourself with these concepts.