Which of the following molecules are likely to form hydrogen bonds: (a) \(\mathrm{PH}_{3}\); (b) \(\mathrm{HBr}\); (c) \(\mathrm{C}_{2} \mathrm{H}_{4}\); (d) \(\mathrm{HNO}_{2}\) ?

Short Answer

Expert verified
Only (d) HNO2 is likely to form hydrogen bonds.

Step by step solution

01

Understand Hydrogen Bonding

Hydrogen bonding is a type of dipole-dipole interaction that occurs between molecules where hydrogen is directly bonded to a highly electronegative atom, particularly nitrogen (N), oxygen (O), or fluorine (F). The molecule with hydrogen attached to N, O, or F can form hydrogen bonds.
02

Analyze Each Molecule for Hydrogen Bonding Capability

(a) PH3: Hydrogen is bonded to phosphorus, which is less electronegative and does not typically participate in hydrogen bonding. (b) HBr: Hydrogen is bonded to bromine, which is not one of the highly electronegative atoms typically involved in hydrogen bonds. (c) C2H4: This molecule has no N, O, or F atoms connected to hydrogen. (d) HNO2: This molecule has hydrogen connected to oxygen, which is electronegative and can participate in hydrogen bonding.
03

Determine Which Molecules Can Form Hydrogen Bonds

Based on the analysis, only (d) HNO2 has the potential to form hydrogen bonds since it contains hydrogen directly bonded to an oxygen atom which is highly electronegative.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electronegativity
Electronegativity is a measure of an atom's ability to attract and hold onto electrons when it is part of a compound. Elements with high electronegativity, such as nitrogen (N), oxygen (O), and fluorine (F), have a strong pull on the electrons in a bond, leading to an uneven distribution of charge. This charge difference creates a partial negative charge on the more electronegative atom and a partial positive charge on the less electronegative atom, such as hydrogen.

Understanding electronegativity is crucial when studying hydrogen bonding, as the large electronegativity difference between hydrogen and elements like N, O, or F is what leads to the creation of a dipole. A dipole is essentially a pair of opposite charges separated by a short distance within a molecule, resulting from this unequal sharing of electrons. As hydrogen bonds are a type of dipole-dipole interaction, molecules that have hydrogens attached to highly electronegative atoms have the potential to form strong hydrogen bonds.
Dipole-Dipole Interactions
Dipole-dipole interactions are forces of attraction that occur between the positive end of one polar molecule and the negative end of another polar molecule. These interactions happen because of the presence of permanent dipoles, which are a result of the differences in electronegativity between atoms within a molecule.

When it comes to hydrogen bonding, which is a special kind of dipole-dipole interaction, the focus is on the strong attraction between the slightly positive hydrogen atom bonded to an electronegative atom (like N, O, or F) and the slightly negative atom of another molecule. This interaction is stronger than a regular dipole-dipole interaction due to the high polarity and the small size of the hydrogen atom, which allows for closer proximity between dipoles. As discussed in the textbook solution, HNO2 can form hydrogen bonds because of the presence of hydrogen attached to the highly electronegative oxygen atom.
Molecular Polarity
Molecular polarity arises from the distribution of electrons across the various atoms in a molecule, which is influenced by the shape of the molecule and the electronegativity of its constituent atoms. In polar molecules, the electrons are unevenly distributed, creating partial charges within the molecule that can interact with other polar molecules or ions.

The polarity of a molecule plays a significant role in its physical properties, including its boiling point, solubility, and the types of chemical reactions it can participate in. For instance, polar molecules tend to be soluble in polar solvents due to the principle of 'like dissolves like,' wherein substances with similar polar characteristics are more likely to be miscible with one another. Moreover, in the context of hydrogen bonding, polar molecules with hydrogen bonded to highly electronegative atoms (N, O, or F) can form stronger intermolecular bonds, leading to higher boiling points and increased solubility in polar solvents compared to nonpolar molecules.

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Most popular questions from this chapter

A commonly occurring mineral has a cubic unit cell in which the metal cations, \(M\), occupy the corners and face centers. Inside the unit cell, anions, A, occupy all the tetrahedral holes created by the cations. What is the empirical formula of the \(\mathrm{M}_{m} \mathrm{~A}_{a}\) compound?

Consider a metallic element that crystallizes in a cubic close-packed lattice. The edge length of the unit cell is \(408 \mathrm{pm}\). If close-packed layers are deposited on a flat surface to a depth (of metal) of \(0.125 \mathrm{~mm}\), how many close-packed layers are present?

Chloromethane \(\left(\mathrm{CH}_{3} \mathrm{Cl}\right)\), methane, and acetic acid \(\left(\mathrm{CH}_{3} \mathrm{COOH}\right)\) form molecular solids. (a) What types of forces hold these molecules in a molecular solid? (b) Place the solids in order of increasing melting point.

The molecular structures of many common liquid crystals are long and rodlike. In addition, they contain polar groups. Explain how both characteristics of liquid crystals contribute to their anisotropic nature.

We have been using "intermolecular interaction" and "intermolecular force" almost interchangeably. However, it is important to distinguish the force from the potential energy of interaction. In classical mechanics, the magnitude of the force, \(F\), is related to the distance dependence of the potential energy, \(E_{\mathrm{P}}\), by \(F=-\mathrm{d} E_{\mathrm{p}} / \mathrm{d} r\). How does the intermolecular force depend on separation for a typical intermolecular interaction that varies as \(1 / r^{6}\) ?

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