Sunday Tutoring Session with Melissa Maribel

Introduction

• Weekly Sunday tutoring sessions focused on chemistry.
• Goal: Help students achieve at least a B grade.
• Sessions are a thank you for subscribers.
• Milestone goal: 10,000 subscribers for an 8-hour live session.

Today's Topic: Molecular Geometry and VSEPR Theory

VSEPR Theory

• Definition: Valence Shell Electron Pair Repulsion.
• Shows how molecular structures are arranged based on electron repulsions.
• Electrons are negative and repel each other, leading to specific geometric arrangements.

Types of Geometries

1. Linear
   • Example: Beryllium structure with 2 bonds, no lone pairs.
   • Geometry: 180 degrees.
2. Trigonal Planar
   • Example: Boron structure with 3 bonds, no lone pairs.
   • Geometry: 120 degrees; becomes bent if lone pairs are added.
3. Tetrahedral
   • Example: CH₄ with 4 bonds, no lone pairs.
   • Geometry: 109 degrees; bond angles decrease with lone pairs.
4. Trigonal Bipyramidal
   • 5 electron groups.
   • Examples: Structures with lone pairs result in seesaw, T-shaped, or linear.
5. Octahedral
   • 6 electron groups.
   • Geometry: 90 degrees; lone pairs alter molecular geometry.

Drawing 3D Structures

• Wedges and Dashes: Wedge = towards you, Dash = away from you.
• VSEPR is about drawing 3D structures in 2D.

Polarity

Electronegativity

• Trend: Increases across a period and up a group.
• Fluorine is the most electronegative element.

Determining Polarity

• Dipole Moment: Represents the "tug of war" in molecules.
• Symmetry: Symmetrical molecules are typically nonpolar.
  • Example: CO₂ is nonpolar.
• Asymmetry: Asymmetrical molecules are polar.
  • Example: H₂O is polar due to lone pairs causing a bent shape.

Recognizing Polar and Non-Polar Molecules

• Linear: Nonpolar if symmetrical (e.g., CO₂); polar if asymmetrical (e.g., HCN).
• Trigonal Planar: Nonpolar if all atoms are the same; otherwise, polar.
• Tetrahedral: Nonpolar if symmetrical (e.g., CH₄); polar if asymmetrical with lone pairs.
• Hydrocarbons: Always nonpolar.

Conclusion

• Session focuses on understanding VSEPR and polarity.
• Encouragement to share the channel for more subscribers.
• Request for feedback on topics for future sessions.