Chemical Bonding Lecture Notes

Introduction

• Lecturer: Chris Harris from Ally Chemistry
• Focus on CIE Topic 3: Chemical Bonding
• Covers:
  • Ionic, Covalent, and Metallic Bonds
  • Hybridization and Orbitals

Ionic Bonding

• Definition: Attraction between oppositely charged ions.
• Example: Sodium (Na) and Chlorine (Cl)
  • Na loses an electron, becomes Na+
  • Cl gains an electron, becomes Cl-
  • Held together by electrostatic attractions.
• Common Ion Charges:
  • Group 1: +1
  • Group 2: +2
  • Group 7: -1
  • Transition metals: Variable charges
• Molecular Ions:
  • Hydroxide (OH-), Nitrate (NO3-), Ammonium (NH4+), etc.
• Ionic Compound Formula Method (Swap and Drop):
  • Swap charges to balance the compound.

Giant Ionic Structures

• Example: Sodium Chloride (NaCl)
  • Cube-shaped, giant repeating pattern.
  • High melting point.
  • Soluble in water, conducts electricity when molten/dissolved.

Covalent Bonding

• Definition: Sharing of valence electrons between non-metal atoms.
• Types:
  • Single, Double, Triple Bonds
• Dative/Coordinate Bonds:
  • One atom donates both electrons.
  • Example: Ammonium ion (NH4+)
• Bond Enthalpy and Length:
  • Shorter bonds have higher bond enthalpy.

Shapes of Molecules

• Determined by the number of bond pairs and lone pairs.
• Examples:
  • Linear, Trigonal Planar, Tetrahedral
  • Bond angles can be affected by lone pairs (e.g., NH3, H2O)

Hybridization and Orbital Theory

• Hybridization involves mixing s and p orbitals.
• Types:
  • sp3, sp2, sp
• Sigma (σ) and Pi (π) Bonds:
  • Sigma: Overlap of orbitals.
  • Pi: Sideways overlap of p orbitals (e.g., in alkenes).

Electronegativity

• Ability of an atom to attract electrons.
• Pauling Scale: Higher value = more electronegative.
• Polar bonds form when there is a difference in electronegativity.

Intermolecular Forces

• Types:
  • Van der Waals (induced dipole-dipole)
  • Permanent Dipole-Dipole
  • Hydrogen Bonding (strongest intermolecular force)
• Hydrogen Bonding: Occurs with N, O, F.

Metallic Bonding

• Definition: Positive metal ions surrounded by a sea of delocalized electrons.
• Properties:
  • High melting/boiling points
  • Conduct electricity
  • Malleable and ductile

Summary

• Review of bond types: Giant covalent (macromolecular), Simple molecular, Ionic, and Metallic bonding.
• Importance of understanding electronegativities and intermolecular forces in chemical reactions and material properties.