Rank the following substances in order of increasing strength of their respective intermolecular forces: CH4, H2O, CO2, NH3.

• A. NH3 < CH4 < CO2 < H2O
• B. CO2 < CH4 < H2O < NH3
• C. CH4 < CO2 < NH3 < H2O
• D. CH4 < NH3 < CO2 < H2O

Answer: (C)

Verified step by step guidance

1. Identify the types of intermolecular forces present in each substance: CH4, H2O, CO2, and NH3. Consider whether they exhibit London dispersion forces, dipole-dipole interactions, or hydrogen bonding.
2. Recognize that CH4 (methane) is a nonpolar molecule, so it primarily exhibits London dispersion forces, which are generally the weakest intermolecular forces.
3. Note that CO2 is a linear, nonpolar molecule with symmetrical charge distribution, so it also mainly exhibits London dispersion forces, but due to its larger size and more electrons compared to CH4, its dispersion forces are stronger.
4. Understand that NH3 (ammonia) is a polar molecule capable of hydrogen bonding because it has a nitrogen atom bonded to hydrogen atoms, which significantly increases its intermolecular force strength compared to CH4 and CO2.
5. Recognize that H2O (water) has the strongest intermolecular forces among the group because it exhibits strong hydrogen bonding due to the highly electronegative oxygen atom bonded to hydrogen atoms, leading to the highest boiling point and strongest intermolecular attractions.