Understanding Electronegativity in Chemistry

Introduction to Electronegativity

• Importance: Fundamental concept in chemistry, especially organic chemistry.
• Definition (by Linus Pauling): "The power of an atom in a molecule to attract electrons to itself."

Electronegativity and the Pauling Scale

• Pauling Scale: Used to measure electronegativity.
• Comparison of Elements:
  • Carbon: 2.5
  • Oxygen: 3.5
  • Difference indicates oxygen is more electronegative than carbon.

Electronegativity in Covalent Bonds

• Polar Covalent Bonds:
  • Oxygen attracts electrons more strongly than carbon, creating a partial negative charge on oxygen and a partial positive charge on carbon.
  • Represented by a delta symbol (δ) for partial charges.
• Non-Polar Covalent Bonds:
  • Occurs when atoms have the same electronegativity, e.g., carbon-carbon bond (2.5 - 2.5 = 0).
  • Electrons are equally shared.

Examples and Interpretation

• Carbon-Hydrogen Bond:
  • Difference of 0.4 (non-polar covalent bond).
• Carbon-Oxygen Bond:
  • Difference of 1.0 (polar covalent bond).
• Oxygen-Hydrogen Bond:
  • Difference of 1.4 (polar covalent bond).
• Carbon-Lithium Bond:
  • Difference of 1.5 (polar covalent, but close to ionic character).
• Sodium-Chlorine Bond:
  • Difference of 2.1 (ionic bond).

Understanding Bond Types

• Electronegativity Difference:

  • 1.7 implies mostly ionic bond.

  • <1.7 implies polar covalent bond.
  • <0.5 implies non-polar covalent bond.
• Relative Nature: The values are relative, not absolute.

Applications in Organic Chemistry

• Importance of Relative Differences: Essential for understanding chemical reactions and mechanisms in organic chemistry.
• Simplified Approach: Focus on relative electronegativity (e.g., oxygen vs. carbon) for chemical processes.