Chemical Bonds, Electronegativity, and Polarity

Overview

• Review of Grade 11 concepts with focus on chemical bonding types: ionic and covalent.
• Importance of electronegativity in determining bond types and polarity.

Electronegativity

• Definition: Tendency of an atom to attract neighboring electrons.
• Analogy: Attractive power like "handsomeness" (e.g., Justin Bieber analogy).
• Periodic Table Trend:
  • Increases across a period (left to right).
  • Increases up a group (bottom to top).
  • Example: Fluorine (high electronegativity), Francium (low electronegativity).
• Relevance: Key to predicting the ionic or covalent nature of bonds.

Types of Bonds

• Ionic Bonds:
  • Formed when the electronegativity difference (ΔEN) > 1.7.
  • Electrons are transferred, not shared.
• Covalent Bonds:
  • Form when the ΔEN < 1.7.
  • Electrons are shared between atoms.
  • Can be polar or nonpolar depending on ΔEN.

Covalent Bonds Subtypes

• Polar Covalent Bonds:
  • ΔEN between 0.5 and 1.7.
  • Unequal sharing of electrons.
  • Results in partial charges (δ+ and δ-) on atoms.
• Nonpolar Covalent Bonds:
  • ΔEN < 0.5.
  • Equal sharing of electrons.
  • Even distribution of electron charge.

Polarity and Dipoles

• Dipole Moment:
  • Occurs in polar molecules due to separation of charges.
  • Represented by an arrow pointing from positive to negative.

Molecule Polarity

• Nonpolar Molecules:
  • Satisfy one of these conditions: symmetrical or low ΔEN (<0.5).
  • Example: CH₄, BF₃, SF₆.
• Polar Molecules:
  • Must satisfy both asymmetry and significant ΔEN.
  • Example: H₂O, NH₃.

Determining Polarity

• Consider symmetry and electronegativity differences.
• Use vector addition for dipole moments in molecules.
• Example exercises demonstrated with various compounds (e.g., HCl, NH₃, CCl₄).

Conclusion

• Understanding of electronegativity and molecular geometry is crucial for predicting bond type and molecule behavior.
• Importance of recognizing the spectrum of bonding (ionic to covalent) and the role of arbitrary thresholds like 1.7 and 0.5.

Key Takeaways

• Electronegativity trends on the periodic table guide predictions of bond types.
• Bond types are on a spectrum rather than discrete categories.
• Molecular polarity impacts chemical properties and interactions.
• Symmetry plays a critical role in determining molecular polarity.