Lecture Notes: Chemical Bonds

Introduction to Chemical Bonds

• Molecules consist of atoms participating in chemical bonds.
• Types of bonds are determined by differences in electronegativity between atoms.

Ionic Bonds

• Formation: Occurs when the electronegativity difference is more than about 2.
  • Example: Sodium and Chlorine.
  • Chlorine (high electronegativity) steals an electron from Sodium (low electronegativity).
  • Result: Formation of positively charged Sodium ion and negatively charged Chloride ion.
• Characteristics:
  • Strong electrostatic attraction between ions with formal charges.
  • Electrons are not shared, they are transferred.

Covalent Bonds

• Formation: Occurs when the electronegativity difference is less than about 1.7.
  • Electrons are shared between atoms rather than transferred.
  • Each electron feels the attraction to the opposite nucleus.
• Types of Covalent Bonds:
  • Polar Covalent Bonds:
    • Electronegativity difference is between about 0.5 and 1.7.
    • Example: Hydrogen and Chlorine.
    • The more electronegative atom (e.g., Chlorine) hogs the electrons.
    • Results in partial charges:
      • More electronegative atom: Partially negative (δ-)
      • Less electronegative atom: Partially positive (δ+)
  • Nonpolar Covalent Bonds:
    • Electronegativity difference is less than 0.5.
    • Electrons are shared evenly.
    • No partial charges.
    • Example: Two atoms of the same element.

Summary

• Predicting Bond Type by Electronegativity:
  • Nonpolar Covalent: Difference < 0.5
  • Polar Covalent: Difference between 0.5 and 1.7
  • Ionic: Difference > 2
• Other bonding phenomena include metallic bonding, but ionic and covalent are the primary types.

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