Sigma and Pi Bonds in Chemical Bonding

Chemical Bonding Overview

  • Covalent Bonds

    • Essential properties:

      • Determined by the nature and properties of the substance.

Types of Covalent Bonds

  • 1. Single Covalent Bonds:  1 pair of electrons shared.   

  • Double Covalent Bonds:    2 pairs of electrons shared.   

  • Triple Covalent Bonds:     3 pairs of electrons shared.   

  • Polar Covalent Bonds:    Unequal sharing of electron pairs.   

  • Non-Polar Covalent Bonds:  Equal sharing of electron pairs.

Covalent Bond Structure

  • A covalent bond forms when atomic orbitals overlap:   

Types of overlapping orbitals:    

 1. Sigma (σ) bonds: Formed by end-to-end overlap of orbitals.     

2. Pi (π) bonds: Formed by side-to-side overlap of orbitals.

  • Example of sigma bond formation:

    • Hydrogen (H) Molecule:

    • Overlap of 1s orbitals.

    • Sigma bond is formed by shared electron pair from individual hydrogen atoms.

Sigma and Pi Bonds Characteristics

Molecule Examples of Bonds:  

 1. H2 Molecule:

  • Has 7 σ bonds and no π bonds.

2. F2 Molecule:     

  • Has 6 σ bonds and 1 π bond.

3. C2H4 (Ethene):     

  •  - Characterized by:        

  • sp² hybridization (2s + 2p orbitals).       

  • 4 σ bonds and 1 π bond.

Specific Examples of Molecules

  1. Hydrogen (H2):   

    • Overlap of 1s orbitals; result in a sigma bond.

  2. Fluorine (F2):  

    • Overlap of 2p orbitals; result in a sigma bond.

  3. Hydrogen Fluoride (HF):   

    • Overlap of 1s (H) and 2p (F) orbitals; result in a sigma bond.

  4. Ethylene (C2H4):   

    • Sigma bond formation:      -

    • Overlap of s and sp² orbitals leading to σ bonds.      -

    • Overlap of p and p orbitals leading to π bond.    -

    • Contains:     

      •  - 4 σ bonds and 1 π bond.

Double and Triple Bonds

  • Double Bonds:

    • Consist of:  

      • One σ bond (greend) formed by end-to-end overlap.     -

      • One π bond formed by side-to-side overlap of p orbitals.   -

      • Shared pairs occur in regions along and above/below the axis joining the nuclei.

  • Triple Bonds:   -

    • Consist of:     -

      • One σ bond formed by end-to-end overlap.     -

      • Two π bonds: one from overlap above/below and one from overlap in front/behind the axis joining the nuclei.

Sigma and Pi Bonds in Molecules

Determine the sigma and pi bonds in the following molecules:   

  1. Molecule 1:**      

    • - Description: _ σ bonds, _ π bond(s)   2. Molecule 2:**

    • Description: _ σ bonds, _ π bond(s)   3. Molecule 3:**

    • Description: _ σ bonds, _ π bond(s)   4. Molecule 4:**

    • Description: _ σ bonds, _ π bond(s)

Conclusion

  • Final Thought: All single covalent bonds are considered sigma bonds, forming through the overlap of various types of orbitals, leading to shared electrons positioned along the axis defined by the nuclei of the bonded atoms.

Definitions

  1. Sigma bond (σ):

    • Formed by the end-to-end overlap of atomic orbitals, allowing for the sharing of a pair of electrons along the axis defined by the bonded atoms.

      • This type of bond is the first bond formed between two atoms and is characterized by a cylindrical symmetry around the bond axis.

  2. pi bond (π)

    • is formed by the side-to-side overlap of p orbitals. It occurs in conjunction with a sigma bond when a double or triple bond is present.

      • Pi bonds have a higher energy than sigma bonds and contribute to the overall strength and properties of the multiple bonds between atoms.