Which of the following molecules has the largest dipole moment?

• A. CO_2
• B. HCl
• C. CH_4
• D. Cl_2

Answer: (B)

Verified step by step guidance

1. Recall that the dipole moment of a molecule depends on both the polarity of its bonds and the molecular geometry, which determines how individual bond dipoles add up vectorially.
2. Analyze each molecule's structure and bond polarity: CO_2 is linear with two polar C=O bonds pointing in opposite directions, which tend to cancel out; CH_4 is tetrahedral with four C-H bonds that are only slightly polar and symmetrically arranged, leading to a near-zero net dipole moment; Cl_2 is a diatomic molecule with identical atoms, so it is nonpolar and has no dipole moment; HCl is a diatomic molecule with a significant difference in electronegativity between H and Cl, resulting in a strong bond dipole.
3. Understand that in CO_2, despite polar bonds, the linear geometry causes the dipoles to cancel, resulting in a net dipole moment of zero.
4. Recognize that CH_4's symmetrical tetrahedral shape causes any small bond dipoles to cancel out, making the molecule nonpolar overall.
5. Conclude that HCl, being a diatomic molecule with a large electronegativity difference and no symmetry to cancel the dipole, has the largest dipole moment among the options.