Which of the following molecules would exhibit a dipole-dipole interaction as shown in a typical dipole-dipole diagram?

• A. HCl
• B. C_2H_6
• C. Cl_2
• D. CH_4

Answer: (A)

Verified step by step guidance

1. Understand that dipole-dipole interactions occur between molecules that have permanent dipole moments, meaning the molecule must be polar with an uneven distribution of electron density.
2. Analyze each molecule's structure and electronegativity differences to determine polarity: HCl has a significant electronegativity difference between H and Cl, making it polar; C_2H_6 (ethane) is nonpolar due to symmetrical distribution; Cl_2 is nonpolar because it consists of two identical atoms sharing electrons equally; CH_4 (methane) is nonpolar due to its symmetrical tetrahedral shape.
3. Recall that nonpolar molecules do not have permanent dipoles and therefore do not exhibit dipole-dipole interactions, but may exhibit London dispersion forces instead.
4. Conclude that among the given molecules, only HCl has a permanent dipole moment and thus can exhibit dipole-dipole interactions as shown in typical diagrams.
5. Summarize that identifying dipole-dipole interactions requires recognizing molecular polarity, which depends on molecular geometry and differences in electronegativity between bonded atoms.