Question

(a) What atoms must a molecule contain to participate in hydrogen bonding with other molecules of the same kind? (b) Which of the following molecules can form hydrogen bonds with other molecules of the same kind: \(\mathrm{CH}_{3} \mathrm{~F}, \mathrm{CH}_{3} \mathrm{NH}_{2}, \mathrm{CH}_{3} \mathrm{OH}, \mathrm{CH}_{3} \mathrm{Br} ?\)

Short answer

(a) A molecule must contain a hydrogen atom (H) covalently bonded to a highly electronegative atom (F, O, or N) and have a lone pair of electrons on the electronegative atom to participate in hydrogen bonding with other molecules of the same kind. (b) The molecules \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) and \(\mathrm{CH}_{3} \mathrm{OH}\) can form hydrogen bonds with other molecules of the same kind.

Step-by-step solution

Understanding Hydrogen Bonding

Hydrogen bonding is a strong type of intermolecular force that occurs when a hydrogen atom that is covalently bonded to a highly electronegative atom (such as fluorine, oxygen, or nitrogen) interacts with the electronegative atom of another molecule. To participate in hydrogen bonding, a molecule must have two essential features: 1. A hydrogen atom (H) covalently bonded to a highly electronegative atom (F, O, or N) 2. A lone pair of electrons on the highly electronegative atom, which will provide the site for hydrogen bonding to occur.

Identify Molecules Capable of Hydrogen Bonding

Now, let's examine the given molecules to determine which of them can form hydrogen bonds with other molecules of the same kind: a) \(\mathrm{CH}_{3} \mathrm{F}\) This molecule has a hydrogen atom, but it is not bonded to fluorine, oxygen, or nitrogen. C-H bonds are not highly polar, hence there can't be hydrogen bonding in this molecule. b) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) This molecule has two N-H bonds with N being a highly electronegative atom. There is also a lone pair of electrons on the nitrogen atom, which enables hydrogen bonding to occur between this molecule and other similar molecules. c) \(\mathrm{CH}_{3} \mathrm{OH}\) Here, the hydrogen atom is bonded to an oxygen atom, which is highly electronegative. Oxygen has two lone pairs of electrons, thus allowing hydrogen bonding to occur between this molecule and other similar molecules. d) \(\mathrm{CH}_{3} \mathrm{Br}\) In this molecule, while the hydrogen atom is present, it is not bonded to a highly electronegative atom (F, O, or N). Therefore, hydrogen bonding cannot occur between this molecule and other similar molecules.

Answer

(a) To participate in hydrogen bonding with other molecules of the same kind, a molecule must contain a hydrogen atom covalently bonded to a highly electronegative atom (F, O, or N) and have a lone pair of electrons on the electronegative atom. (b) The following molecules can form hydrogen bonds with other molecules of the same kind: \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) and \(\mathrm{CH}_{3} \mathrm{OH}\).