Problem 23 - Chemistry: The Central Science

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: \(\mathrm{CH}_{3} \mathrm{~F}, \mathrm{CH}_{3} \mathrm{NH}_{2}, \mathrm{CH}_{3} \mathrm{OH}, \mathrm{CH}_{3} \mathrm{Br} ?\)

Step-by-Step Solution

Answer

(a) A molecule must contain hydrogen atoms bonded to fluorine, oxygen, or nitrogen 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 that can form hydrogen bonds with other molecules of the same kind are \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) and \(\mathrm{CH}_{3} \mathrm{OH}\).

Step 1: Identify the criteria for hydrogen bonding

For a molecule to participate in hydrogen bonding with other molecules of the same kind, it must possess two features: 1. A hydrogen atom bonded to a highly electronegative atom, such as fluorine (F), oxygen (O), or nitrogen (N). This is because these atoms, when bonded to a hydrogen atom, attract the electron density between them, creating a partial positive charge on the hydrogen atom. 2. A lone pair of electrons on the electronegative atom (F, O, or N) that can attract the partially positive charged hydrogen atoms of other molecules and form a non-covalent bond - the hydrogen bond. #a# Thus, a molecule must contain hydrogen atoms bonded to fluorine, oxygen, or nitrogen and have a lone pair of electrons on the electronegative atom to participate in hydrogen bonding with other molecules of the same kind.

Step 2: Identify which of the given molecules can form hydrogen bonds

Now that we know the criteria for hydrogen bonding, let's analyze each of the given molecules: 1. \(\mathrm{CH}_{3} \mathrm{F}\): The hydrogen atoms are bonded to carbon, not fluorine, so it doesn't satisfy the first criterion. 2. \(\mathrm{CH}_{3} \mathrm{NH}_{2}\): The hydrogen atoms are bonded to nitrogen, and nitrogen has a lone pair of electrons. This molecule satisfies both criteria and can form hydrogen bonds. 3. \(\mathrm{CH}_{3} \mathrm{OH}\): The hydrogen atoms are bonded to oxygen, and oxygen has two lone pairs of electrons. This molecule satisfies both criteria and can form hydrogen bonds. 4. \(\mathrm{CH}_{3} \mathrm{Br}\): The hydrogen atoms are bonded to carbon, not bromine, so it doesn't satisfy the first criterion.

Step 3: Consolidate the answer

Only the molecules that satisfy both hydrogen bonding criteria can form hydrogen bonds with other molecules of the same kind. Based on our analysis, the molecules that can form hydrogen bonds are: \(b\) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) and \(\mathrm{CH}_{3} \mathrm{OH}\) Thus, these are the molecules that can form hydrogen bonds with other molecules of the same kind.