Problem 25 - 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 H-O, H-N, or H-F bonds to participate in hydrogen bonding with other molecules of the same kind. (b) \(\mathrm{CH}_{3}\mathrm{F}\), \(\mathrm{CH}_{3}\mathrm{NH}_{2}\), and \(\mathrm{CH}_{3}\mathrm{OH}\) can form hydrogen bonds with other molecules of the same kind. \(\mathrm{CH}_{3}\mathrm{Br}\) cannot.

Step 1: Understanding Hydrogen Bonding

Hydrogen bonding is a type of intermolecular interaction that occurs between a highly electronegative atom (usually oxygen, nitrogen, or fluorine) and a hydrogen atom that is covalently bonded to another highly electronegative atom. To participate in hydrogen bonding, a molecule must have a hydrogen atom bonded to an oxygen, nitrogen, or fluorine atom (H-O, H-N, or H-F bond).

Step 2: Identify Molecules with Hydrogen Bonding Capability

Using the criteria above, we can examine each of the given molecules to determine if they contain the necessary H-O, H-N, or H-F bond required for hydrogen bonding: 1. \(\mathrm{CH}_{3}\mathrm{F}\): This molecule has an H-F bond, which meets the criteria for hydrogen bonding. 2. \(\mathrm{CH}_{3}\mathrm{NH}_{2}\): This molecule has an H-N bond, which meets the criteria for hydrogen bonding. 3. \(\mathrm{CH}_{3}\mathrm{OH}\): This molecule has an H-O bond, which meets the criteria for hydrogen bonding. 4. \(\mathrm{CH}_{3}\mathrm{Br}\): This molecule has an H-Br bond, which does not meet the criteria for hydrogen bonding as Br is not one of the highly electronegative atoms necessary for hydrogen bonding (O, N, or F).

Step 3: Final Answer

Based on the analysis above, we can answer the exercise questions as follows: (a) A molecule must contain hydrogen atoms bonded to one of the highly electronegative atoms (oxygen, nitrogen, or fluorine) in order to participate in hydrogen bonding with other molecules of the same kind. (b) The following molecules can form hydrogen bonds with other molecules of the same kind: \(\mathrm{CH}_{3}\mathrm{F}\), \(\mathrm{CH}_{3}\mathrm{NH}_{2}\), and \(\mathrm{CH}_{3}\mathrm{OH}\). The molecule \(\mathrm{CH}_{3}\mathrm{Br}\) cannot form hydrogen bonds with other molecules of the same kind.

Key Concepts

Intermolecular Forces

Imagine a crowded party where guests represent molecules. Just as these guests might interact through handshakes or conversations, molecules intermingle through attractions known as intermolecular forces. These are not strong covalent bonds that hold atoms together within a molecule; rather, they are gentler forces between separate molecules, akin to the light push you might feel in the crowd.

There are several types of intermolecular forces, with varying strengths, but one of the most significant is hydrogen bonding. To understand hydrogen bonding, consider it as a special handshake that can only occur between molecules where a hydrogen atom is closely acquainted with a VIP electronegative atom like oxygen, nitrogen, or fluorine. This VIP status comes from these atoms' exceptional ability to attract electrons towards themselves.

Hydrogen bonding not only affects the physical properties, like the boiling point and solubility of substances, but also the behavior of molecules in biological systems. For instance, the remarkable characteristics of water are largely due to these bonds. The hydrogen bonds between water molecules give it a high boiling point and surface tension, which is why water can capture insects skimming on its surface or climb upwards in plants against gravity.

Electronegativity

Electronegativity is a bit like the charisma of atoms, referring to their magnetic pull on shared electrons in a bond. Think of it as two friends holding a pizza slice (representing shared electrons): the one with the greater hunger (electronegativity) will pull more of the slice towards themselves.

In the periodic table's theater, the closer atoms are to the upper right corner (excluding the noble gases), the more electronegative they are. Thus, fluorine is the king of electronegativity, with oxygen and nitrogen as nobility. When these electronegative atoms form a relationship with a hydrogen atom, they may foster a special intermolecular force: hydrogen bonding. Why does this matter? The distribution of electron density in molecules affects their chemistry, reactivity, and their ability to form hydrogen bonds. If you've ever noticed water droplets clinging to a surface or DNA’s double helix structure, you've seen electronegativity and hydrogen bonding in action.

Chemical Bonding

The robust framework that constitutes the world’s substances is all thanks to chemical bonding. It’s comparable to constructing with building blocks where atoms are the blocks, and the connections between them are the various types of bonds. Chemical bonds come in multiple forms, like the hearty handshake of covalent bonds where atoms share electrons or the formal nod of ionic bonds resulting from the transfer of electrons.

Within covalent bonds, there's variance too. In our previous exercise, hydrogen bonds were highlighted. They are the cordial acknowledgments between molecules where a hydrogen covalently attached to one atom nods towards an electronegative neighbor. Yet, they are just one type of interaction within the vast world of chemical bonding. Understanding the specific conditions and types of atoms involved helps us discern why some substances act like social butterflies, sticking and interacting with others, while some stay as loners, barely affected by their surrounds. And just as handshakes differ in firmness and formality, so do chemical bonds in strength and function.