Question

Which compounds can participate in hydrogen bonding with water? State which compounds can act only as hydrogen-bond donors, which can act only as hydrogen-bond acceptors, and which can act as both hydrogen-bond donors and hydrogen-bond acceptors.

Short answer

Answer: Compounds that can participate in hydrogen bonding with water include water (H2O), ammonia (NH3), hydrogen fluoride (HF), and chloride ion (Cl-). Water and ammonia are classified as both hydrogen-bond donors and acceptors, while hydrogen fluoride is a hydrogen-bond donor, and chloride ion is a hydrogen-bond acceptor.

Step-by-step solution

Identify the molecule as a hydrogen-bond donor, acceptor, or both

To identify which compounds can participate in hydrogen bonding with water, first, we need to examine the electronegative atoms and the bonding of hydrogen to these atoms in the molecule. Water is a molecule with an oxygen atom covalently bonded to two hydrogen atoms (H2O). Oxygen is an electronegative atom with two lone pairs of electrons. Thus, water can act as both a hydrogen-bond donor (with its hydrogen atoms) and a hydrogen-bond acceptor (with its oxygen lone pair electrons). We can apply this understanding to other molecules as we classify them.

Identify compounds as hydrogen-bond donors

A hydrogen-bond donor contains a hydrogen atom covalently bonded to an electronegative atom such as oxygen, nitrogen, or fluorine. Some examples of hydrogen-bond donor compounds include: 1. Ammonia (NH3): Nitrogen is covalently bonded to three hydrogen atoms. 2. Hydrogen fluoride (HF): Fluorine is covalently bonded to one hydrogen atom.

Identify compounds as hydrogen-bond acceptors

A hydrogen-bond acceptor molecule has an electronegative atom with a lone pair of electrons. Some examples of hydrogen-bond acceptor compounds include: 1. Ammonia (NH3): Nitrogen has one lone pair of electrons. 2. Chloride ion (Cl-): Chlorine is an electronegative atom with three lone pairs of electrons.

Identify compounds as both hydrogen-bond donors and acceptors

Some compounds can act as both hydrogen-bond donors and acceptors due to the presence of both a hydrogen atom covalently bonded to an electronegative atom and an electronegative atom with lone pairs of electrons. Examples include: 1. Water (H2O): The oxygen is bonded to two hydrogen atoms and has two lone pairs of electrons. 2. Ammonia (NH3): The nitrogen is covalently bonded to three hydrogen atoms and has one lone pair of electrons. In conclusion, based on the understanding of hydrogen bonding and the classification of compounds, we can identify the possible interactions between different molecules and water. These interactions can be hydrogen-bond donations, acceptances, or both.

Key concepts

Hydrogen-Bond Donors

Understanding the role of hydrogen-bond donors is crucial when exploring the intricate world of intermolecular forces. A hydrogen-bond donor is fundamentally a molecule that has a hydrogen atom attached to a highly electronegative element, often nitrogen (N), oxygen (O), or fluorine (F). These electronegative atoms pull electron density away from the hydrogen atom, creating a slightly positive charge on the hydrogen, ideal for forming hydrogen bonds.

To illustrate, think of ammonia (NH₃), with its nitrogen atom bound to three slightly positively charged hydrogen atoms. Similar is hydrogen fluoride (HF), where fluorine, being one of the most electronegative elements, is linked to hydrogen. Each of these molecules can donate a hydrogen to engage in a hydrogen bond with a suitable acceptor, such as the lone pair of electrons in the oxygen of water.

Hydrogen-Bond Acceptors

In contrast to donors, hydrogen-bond acceptors are molecules that possess electronegative atoms with one or more lone pairs of electrons, keen on accepting hydrogen bonds. These atoms have regions of negative charge due to the nonbonding electrons, making them perfect candidates for accepting hydrogen bonds.

Looking at examples such as ammonia (NH₃), we see that its nitrogen atom not only contributes hydrogen atoms for bonding but also offers a lone pair of electrons that can act as a hydrogen-bond acceptor. Similarly, a chloride ion (Cl^-) is a classic acceptor with its three lone pairs on the chlorine atom, ready to form hydrogen bonds with compatible donors.

Intermolecular Forces

The forces that hold different molecules together are termed as intermolecular forces. These include hydrogen bonds, which are some of the strongest intermolecular attractions, surpassing in strength the Van der Waals forces, although they are not as strong as ionic or covalent bonds.

Hydrogen bonds are highly directional and involve a link between a hydrogen-bond donor's hydrogen atom and a hydrogen-bond acceptor's lone pair of electrons. These special interactions have profound effects on the physical properties of compounds, such as boiling points, solubility, and even the unique structure of DNA.

Electronegativity

One more piece to grasp the puzzle of hydrogen bonds lies in understanding electronegativity. It's a measure of an atom's ability to attract and hold onto electrons. Atoms with high electronegativity, like oxygen, nitrogen, and fluorine, are more likely to pull electrons towards themselves within a covalent bond, creating polarity in the molecule.

The differences in electronegativity between hydrogen and these atoms enable the hydrogen bond formation since the more electronegative atoms induce a positive partial charge on the hydrogen. This charge disparity is the fundamental reason behind the dynamic interplay between hydrogen-bond donors and acceptors in substances and is key to solving why certain compounds can participate in hydrogen bonding with water.