Which of the following molecules contains polar bonds but is overall nonpolar?

• A. H2O
• B. NH3
• C. CH4
• D. CO2

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the difference between polar bonds and overall molecular polarity. A polar bond occurs when there is a difference in electronegativity between two bonded atoms, causing a dipole moment. Overall molecular polarity depends on both the polarity of individual bonds and the geometry of the molecule.
2. Step 2: Identify which bonds in each molecule are polar by comparing electronegativities of the atoms involved. For example, in CO2, the C=O bonds are polar because oxygen is more electronegative than carbon.
3. Step 3: Analyze the molecular geometry of each molecule to determine if the individual bond dipoles cancel out. CO2 has a linear shape, so the two polar C=O bonds are oriented 180° apart, causing their dipoles to cancel each other out.
4. Step 4: Compare this with other molecules: H2O is bent, NH3 is trigonal pyramidal, and CH4 is tetrahedral. In H2O and NH3, the bond dipoles do not cancel, making the molecules polar. In CH4, the bonds are between carbon and hydrogen, which have very similar electronegativities, so the bonds are essentially nonpolar.
5. Step 5: Conclude that CO2 contains polar bonds but is overall nonpolar due to its linear geometry causing dipole cancellation.