AP Chemistry Questions on Lewis Dot Structures

📚 Quick Study Guide

• ⚛️ Lewis Dot Structures represent valence electrons as dots around an element symbol.
• 🔗 Each dot represents one valence electron.
• 🤝 Atoms form bonds to achieve a stable octet (8 valence electrons), except for hydrogen which aims for a duet (2 electrons).
• 📝 Steps to draw Lewis Structures:
  1. Calculate the total number of valence electrons.
  2. Draw a skeletal structure, connecting atoms with single bonds.
  3. Distribute remaining electrons as lone pairs to fulfill the octet rule.
  4. Form multiple bonds (double or triple) if necessary to satisfy octets.
• 💡 Formal Charge = (Valence Electrons) - (Non-bonding Electrons) - (1/2 Bonding Electrons). Aim for minimal formal charges.
• 🧪 Resonance structures occur when multiple valid Lewis structures can be drawn for the same molecule.
• 📐 VSEPR Theory predicts molecular geometry based on minimizing electron pair repulsion. Common geometries: linear, trigonal planar, tetrahedral, bent, trigonal pyramidal.

Practice Quiz

1. What is the total number of valence electrons in $CO_2$?
• A) 12
• B) 16
• C) 18
• D) 20
2. Which of the following elements can have an expanded octet?
• A) Nitrogen
• B) Oxygen
• C) Fluorine
• D) Sulfur
3. What is the molecular geometry of $BF_3$?
• A) Tetrahedral
• B) Trigonal Pyramidal
• C) Trigonal Planar
• D) Bent
4. How many lone pairs of electrons are on the central atom in $H_2O$?
• A) 0
• B) 1
• C) 2
• D) 3
5. What is the formal charge on the nitrogen atom in $NH_4^+$?
• A) -1
• B) 0
• C) +1
• D) +2
6. Which of the following molecules is nonpolar despite having polar bonds?
• A) $H_2O$
• B) $NH_3$
• C) $CO_2$
• D) $SO_2$
7. Which of the following molecules exhibits resonance?
• A) $CH_4$
• B) $H_2O$
• C) $O_3$
• D) $NH_3$