Introduction to Sigma and Pi Bonds

Key Concepts:

• Single Bond: Composed of 1 sigma bond.
• Double Bond: Composed of 1 sigma and 1 pi bond.
• Triple Bond: Composed of 1 sigma and 2 pi bonds.

Sigma and Pi Bonds Formation:

• Sigma Bonds: Formed from the overlap of atomic orbitals.

  • Example: Ethene (C2H4)
    • Ethene has 5 sigma bonds.
    • Carbon in ethene is sp2 hybridized.
    • Hydrogen has an s hybridization.
    • Sigma bonds result from the mixing of s orbital with sp2 orbital.

• Pi Bonds: Arise from unhybridized p orbitals above and below the sigma bond level.

Lewis Structure Examples:

Example: Ethene (C2H4)

• Contains 5 sigma bonds and 1 pi bond.

Example: Acetylene (C2H2)

• Lewis Structure: Linear due to the triple bond between carbons.
• Bond Count:
  • 3 Sigma bonds
  • 2 Pi bonds

Example: Formaldehyde (CH2O)

• Lewis Structure:
  • Carbon is at the center forming 4 bonds.
  • Hydrogen forms single bonds.
  • Oxygen forms two bonds.
• Bond Count:
  • 3 Sigma bonds
  • 1 Pi bond

Example: SO2Cl2

• Lewis Structure:
  • Sulfur can form up to 6 bonds.
  • Oxygen forms two bonds.
  • Chlorine forms one bond.
• Bond Count:
  • 4 Sigma bonds
  • 2 Pi bonds

Counting Sigma and Pi Bonds:

• To find the number of sigma bonds, count each bond.
• To find pi bonds in double or triple bonds, recognize:
  • Each double bond contains 1 pi bond.
  • Each triple bond contains 2 pi bonds.

Tips:

• Hydrogen forms only single bonds.
• Carbon typically forms 4 bonds.
• Utilize symmetry in drawing structures to simplify visualization of bond counts.

Use this guide to draw Lewis structures and count sigma and pi bonds effectively!