Why are hydrogen bonds considered a special class of dipole-dipole interactions?

• A. Because they involve the sharing of electrons between hydrogen and another atom.
• B. Because they occur only between molecules containing hydrogen and highly electronegative atoms such as N, O, or F, resulting in unusually strong attractions.
• C. Because they only occur in nonpolar molecules.
• D. Because they are weaker than all other types of dipole-dipole interactions.

Answer: (B)

Verified step by step guidance

1. Understand that dipole-dipole interactions are forces between polar molecules where partial positive and negative charges attract each other.
2. Recognize that hydrogen bonding is a special type of dipole-dipole interaction that occurs specifically when hydrogen is covalently bonded to highly electronegative atoms like nitrogen (N), oxygen (O), or fluorine (F).
3. Note that these highly electronegative atoms create a strong partial negative charge, while the hydrogen atom carries a strong partial positive charge, leading to a much stronger attraction than typical dipole-dipole forces.
4. Realize that hydrogen bonds are stronger than regular dipole-dipole interactions because the small size of hydrogen allows the positive charge to get very close to the lone pairs on N, O, or F atoms in neighboring molecules.
5. Conclude that hydrogen bonds are considered a special class of dipole-dipole interactions due to their unique strength and the specific requirement of hydrogen bonded to N, O, or F, which is not the case for general dipole-dipole interactions.