Lecture Notes: Covalent Bonds, Hybridization, and Molecular Structure

Introduction to Covalent Bonds

• Formation of Covalent Bonds

  • Two hydrogen atoms approach and react to form a covalent bond.
  • Electrons are shared between atoms in a covalent bond.
  • Represented by a single bond or two electrons between atoms.

• Electrons as Waves

  • Electrons can be thought of as waves.
  • Covalent bonds form from the overlap of atomic orbitals (regions with high probability of electron presence).
  • In-phase waves interfere constructively, creating larger amplitude waves and forming a bond.
  • Out-of-phase waves interfere destructively, leading to a node (region of zero electron density).

Valence Bond Theory

• Concepts

  • Covalent bond: Sharing of electron density due to constructive interference of atomic orbitals.

• Example: Hydrogen Atoms

  • Hydrogen's electron configuration: 1s1.
  • Spherical s orbital.
  • Overlapping orbitals form a sigma bond.
  • All single bonds are sigma bonds.

Hybridization

• Carbon Atom Hybridization

  • Carbon electron configuration: 1s2 2s2 2p2.
  • 6 total electrons, 2 are core electrons, 4 valence electrons.

• Energy Levels and Hybridization

  • Ground state electron configuration: 1s, 2s, 2p sublevels.
  • During hybridization, 2s and 3 2p orbitals mix to form sp3 orbitals.
  • Sp3 orbitals: 4 degenerate orbitals with same energy level.
  • Sp3 orbitals: 25% s character, 75% p character.

• Hybrid Orbitals

  • Sp3 orbitals lower in energy than 2p sublevel.
  • Mixing atomic orbitals results in hybrid orbitals with properties between s and p.

Molecular Structure Examples

• Methane (CH4)

  • Carbon forms four sp3 hybrid orbitals.
  • Each hydrogen forms an s orbital.
  • Methane has four sigma bonds (single bonds/covalent bonds).
  • Hybridization of carbon: sp3.
  • Bond description: s sp3 hybrid.

• Ethane (C2H6)

  • Contains seven sigma bonds.
  • Carbon hybridization: sp3.

Quick Methods to Determine Hybridization

• Carbon Hybridization Rules

  • Carbon attached to 4 atoms: sp3 (1+3=4).
  • Carbon attached to 3 atoms: sp2 (1+2=3).
  • Carbon attached to 2 atoms: sp (1+1=2).

• Hydrogen Orbital Description

  • Hydrogen's atomic orbital: s.

These notes cover the basic principles of covalent bonding, orbital hybridization, and examples with methane and ethane, providing methods to determine hybridization in molecules.