Lecture Notes: Electronegativity in Chemistry

Introduction

• Electronegativity: Key concept in inorganic chemistry.
• Definition by Linus Pauling: "The power of an atom in a molecule to attract electrons to itself."
• Used to compare atoms within a molecule.

Pauling Scale

• Developed by Linus Pauling to compare electronegativity of elements.
• Important values:
  • Carbon: 2.5
  • Oxygen: 3.5

Comparing Electronegativity

Carbon vs. Oxygen

• Oxygen (3.5) is more electronegative than Carbon (2.5).
• Electrons in covalent bonds are shared unequally:
  • Oxygen pulls electrons closer, acquiring a partial negative charge (( \delta^- )).
  • Carbon becomes partially positive (( \delta^+ )).
• This leads to a polar covalent bond.

Carbon vs. Carbon

• Both carbons have the same electronegativity (2.5).
• Electrons are shared equally.
• This results in a non-polar covalent bond.

Carbon vs. Hydrogen

• Carbon: 2.5, Hydrogen: 2.1
• Small difference (0.4) still considered a non-polar covalent bond.

Electronegativity Differences and Bond Types

• Non-Polar Covalent Bond: Difference in electronegativity is less than 0.5.
• Polar Covalent Bond: Difference in electronegativity is more than 0.5.
• Ionic Bond: Difference in electronegativity is typically greater than 1.7.

Examples of Bonds

Oxygen vs. Hydrogen

• Oxygen: 3.5, Hydrogen: 2.1, Difference: 1.4
• Results in a polar covalent bond.

Carbon vs. Lithium

• Carbon: 2.5, Lithium: 1, Difference: 1.5
• Treated as polar covalent but can also be ionic depending on context.

Sodium vs. Chlorine

• Sodium: 0.9, Chlorine: 3, Difference: 2.1
• Electrons are completely transferred from Sodium to Chlorine.
• Results in an ionic bond.

Important Considerations

• Multiple scales for electronegativity exist; Pauling scale is used here.
• Values are relative, not absolute.
• Bond classifications (polar, non-polar, ionic) can vary based on context.

Conclusion

• Understanding electronegativity helps in predicting molecular behavior.
• Focus on relative differences rather than absolute numbers in chemical reactions.
• Key takeaway: Oxygen is more electronegative than carbon, crucial for organic chemistry mechanisms.