Which of the following formulas represents a molecule that is overall nonpolar due to its symmetric shape and cancellation of bond dipoles?

Introduction / Context:
Molecular polarity depends on both bond polarity and molecular geometry. Even if all individual bonds are polar, a molecule can be nonpolar if the shape is highly symmetric and the bond dipoles cancel each other out. Polarity affects properties such as boiling point, solubility and intermolecular forces. This question asks which of the given molecular formulas corresponds to a nonpolar molecule, taking into account both bond polarity and overall shape.

Given Data / Assumptions:

• H2O is known to be a bent molecule with polar O–H bonds.
• CF4 is a tetrahedral molecule with four C–F bonds.
• HCl is a diatomic molecule with a bond between hydrogen and chlorine.
• H2S is a bent molecule similar in shape to water.
• NH3 is trigonal pyramidal with a lone pair on nitrogen.

Concept / Approach:
Bond polarity arises from differences in electronegativity between bonded atoms, creating bond dipoles. Whether the molecule is polar depends on the vector sum of these dipoles. In highly symmetric shapes, such as tetrahedral with identical bonds or linear molecules with equal dipoles in opposite directions, the dipoles can cancel, leading to a nonpolar molecule. In bent or pyramidal shapes, the dipoles usually do not cancel, and the molecule is polar. The approach is to consider each molecule's shape and bond polarity, then identify the one where all bond dipoles cancel due to symmetry.

Step-by-Step Solution:
Step 1: H2O has two polar O–H bonds and a bent geometry, so the dipoles do not cancel; water is polar. Step 2: CF4 has four polar C–F bonds arranged symmetrically in a tetrahedral shape around the central carbon atom. Step 3: Because the four identical C–F bond dipoles are symmetrically oriented, their vector sum is zero, making CF4 nonpolar overall despite each bond being polar. Step 4: HCl is a simple diatomic molecule with a significant electronegativity difference between hydrogen and chlorine, so the molecule has a dipole and is polar. Step 5: H2S is bent, similar to H2O, and has polar H–S bonds, resulting in a net dipole and a polar molecule. Step 6: NH3 is trigonal pyramidal with a lone pair on nitrogen, making it polar due to an uneven distribution of charge. Step 7: Therefore, CF4 is the only molecule in the list that is overall nonpolar.

Verification / Alternative check:
Molecular polarity data from reference books confirm that water, hydrogen chloride, hydrogen sulfide and ammonia all have measurable dipole moments, indicating they are polar. Carbon tetrafluoride, CF4, despite having highly polar C–F bonds, has a very small or negligible dipole moment because the tetrahedral arrangement cancels the bond dipoles. CF4 is often used as a textbook example of a nonpolar molecule with polar bonds. Compare CF4 with CH4, which is also tetrahedral and nonpolar, reinforcing the idea that symmetry can cancel dipoles.

Why Other Options Are Wrong:
Option A, H2O, is polar because its bent shape prevents cancellation of O–H bond dipoles. Option C, HCl, is a polar diatomic molecule with a clear separation of charge between H and Cl. Option D, H2S, has a bent geometry and polar bonds, making it polar. Option E, NH3, with a trigonal pyramidal shape and lone pair, is polar and interacts strongly with water through hydrogen bonding. Only option B, CF4, combines a symmetric tetrahedral shape with identical polar bonds in such a way that all bond dipoles cancel and the molecule is overall nonpolar.

Common Pitfalls:
Students sometimes assume that if all bonds are polar, the molecule must be polar, forgetting the role of geometry. Another pitfall is to think that tetrahedral molecules are always polar because of their three dimensional shape. To avoid these errors, always consider both bond polarity and molecular geometry. Ask whether the polar bonds are arranged symmetrically around the central atom. If they are, as in CF4 or CO2, the molecule can be nonpolar even though individual bonds are polar.

Final Answer:
The formula that represents a nonpolar molecule is CF4, a tetrahedral molecule with four identical C–F bonds whose bond dipoles cancel due to symmetry.