Predicting Polarity Based on Lewis Structures: Examples and Tips

📚 Quick Study Guide

🔍 Polarity depends on both the shape of the molecule and the polarity of its bonds. 💡 To determine polarity: * Draw the Lewis structure. * Determine the molecular geometry using VSEPR theory. * Identify polar bonds based on electronegativity differences. * Consider the symmetry of the molecule. If bond dipoles cancel, the molecule is nonpolar. If they don't, it's polar. 🧪 Key Electronegativity Differences: * Nonpolar Covalent: 0 - 0.4 * Polar Covalent: 0.4 - 1.7 * Ionic: > 1.7 ⚛️ Molecular Geometry Examples: * Linear ($AX_2$): Can be polar or nonpolar (depends on the atoms attached) * Trigonal Planar ($AX_3$): Nonpolar if all atoms are the same; polar if different. * Tetrahedral ($AX_4$): Nonpolar if all atoms are the same; polar if different. * Bent ($AX_2E_2$): Always polar. * Pyramidal ($AX_3E$): Always polar.

🧪 Practice Quiz

1. Which of the following molecules is nonpolar?
1. A. $H_2O$
2. B. $NH_3$
3. C. $CO_2$
4. D. $SO_2$
2. Which of the following molecules has polar bonds but is nonpolar overall?
1. A. $HCl$
2. B. $H_2S$
3. C. $BF_3$
4. D. $PH_3$
3. What is the molecular geometry of $CH_4$?
1. A. Bent
2. B. Trigonal Pyramidal
3. C. Tetrahedral
4. D. Trigonal Planar
4. Which of the following bonds is the MOST polar?
1. A. C-H
2. B. O-H
3. C. N-H
4. D. F-H
5. Which of the following molecules is polar due to its asymmetrical shape and polar bonds?
1. A. $CCl_4$
2. B. $CS_2$
3. C. $CHCl_3$
4. D. $CO_2$
6. What factor primarily determines the polarity of a bond?
1. A. Bond length
2. B. Electronegativity difference
3. C. Atomic mass
4. D. Number of valence electrons
7. Which of the following molecules has a linear shape and is polar?
1. A. $BeCl_2$
2. B. $CO_2$
3. C. $OCS$
4. D. $C_2H_2$