Ionic and Covalent Bonds Lecture

Types of Bonds

1. Ionic Bonds

   • Occurs between a metal and a non-metal.
   • Electrons are transferred from one atom to another.
   • Example: Sodium Chloride (NaCl)
     • Sodium (Na) loses an electron to become a cation (+).
     • Chlorine (Cl) gains an electron to become an anion (-).
   • The electrostatic force of attraction between oppositely charged ions forms the bond.

2. Covalent Bonds

   • Occurs between two non-metals.
   • Electrons are shared between atoms.
   • Non-polar Covalent Bonds
     • Electrons are shared equally.
     • Occurs when bonding atoms have the same electronegativity.
     • Example: Hydrogen molecule (H2)
       • Bond between two hydrogen atoms.
   • Polar Covalent Bonds
     • Electrons are shared unequally.
     • Occurs when there is a difference in electronegativity.
     • Example: Carbon-Oxygen bond
       • Carbon (2.5) and Oxygen (3.5), Difference = 1.0
     • Hydrogen Bonds: Special polar covalent bond when hydrogen is bonded to nitrogen, oxygen, or fluorine.
       • Example: Water (H2O)

Electronegativity

• Measure of an atom's ability to attract electrons in a bond.
• Common values:
  • Hydrogen (H): 2.1
  • Boron (B): 2.0
  • Carbon (C): 2.5
  • Nitrogen (N): 3.0
  • Oxygen (O): 3.5
  • Fluorine (F): 4.0
• Determining Bond Type:
  • Polar Covalent: Electronegativity difference ≥ 0.5
  • Non-Polar Covalent: Electronegativity difference ≤ 0.4

Examples

• Carbon-Hydrogen Bond
  • Electronegativity difference = 0.4
  • Non-polar covalent bond.
• Carbon-Carbon Bond
  • Electronegativity difference = 0
  • Non-polar covalent bond.
• Oxygen-Hydrogen Bond
  • Electronegativity difference = 1.4
  • Polar covalent bond with hydrogen bonding.
• Lithium-Fluorine Bond
  • Ionic bond due to the combination of a metal and a non-metal.

Bond Polarity and Dipole Moments

• Indicate bond polarity using arrows pointing towards the more electronegative atom.
• Partial charges:
  • More electronegative elements have a partial negative charge.
  • Less electronegative elements have a partial positive charge.

Key Concepts

• Metals + Non-metals ➜ Ionic Bonds
• Non-metals + Non-metals ➜ Covalent Bonds (polar or non-polar)