Question

Which of these statements are false: (a) Dipole-dipole interactions between molecules are greatest if the molecules possess only temporary dipole moments. (b) All compounds containing hydrogen atoms can participate in hydrogen bond formation. (c) Dispersion forces exist between all atoms, molecules, and ions. (d) The extent of ion-induced dipole interaction depends only on the charge on the ion.

Short answer

Statement (a), statement (b) and statement (d) are false, while statement (c) is true.

Step-by-step solution

Analyze Statement (a)

Dipole-dipole interactions occur between polar molecules, not those with only temporary dipole moments. Molecules with temporary dipoles participate in London dispersion forces. So, statement (a) is false.

Analyze Statement (b)

Hydrogen bonding is a specific form of dipole-dipole interaction that occurs when hydrogen is bonded to three highly electronegative elements: fluorine, oxygen or nitrogen. Not all compounds with hydrogen atoms can participate in hydrogen bonding. For example, Methane (CH4) cannot form hydrogen bonds. Thus, statement (b) is also false.

Analyze Statement (c)

Dispersion forces or London forces are the weakest type of intermolecular forces and are present between all atoms and molecules regardless of polarity. They result from temporary fluctuations in electron distribution in atoms and molecules. Hence, statement (c) is true.

Analyze Statement (d)

Ion-induced dipole interaction occurs between an ion and a non-polar molecule. This interaction depends not only on the charge of the ion but also on the polarizability of the non-polar molecule. Therefore, statement (d) is false.

Key concepts

Dipole-Dipole Interactions

Dipole-dipole interactions are forces that occur between molecules that have permanent dipole moments. A molecule with a permanent dipole has regions of partial positive and negative charge due to the uneven distribution of electrons within the molecule, which is most often a result of the molecule's shape and the electronegativity differences between atoms.

For instance, consider water molecules, which have a bent shape due to which the oxygen atom, being more electronegative, pulls the electron cloud towards itself, leaving the hydrogen atoms with a partial positive charge. These charged regions are attracted to the oppositely charged regions of adjacent molecules, resulting in a dipole-dipole interaction. This attraction aligns the molecules to maximize the attraction and minimize the repulsion between them.

These interactions are significant in polar molecules and lend themselves to many of the physical properties we observe, such as the elevated boiling points of polar substances compared to nonpolar substances with similar molecular weights.

London Dispersion Forces

London dispersion forces, also known as dispersion forces or Van der Waals forces, are weak intermolecular forces that arise from quantum-induced instantaneous polarization of charge distribution in neutral atoms and nonpolar molecules.

Even in molecules where there's no permanent dipole, electrons move in such a way that there can be brief instants when parts of a molecule are momentarily more negative or positive. These temporary dipoles can induce dipoles in adjacent molecules, thus leading to an attraction between them.

• All atoms and molecules exhibit London dispersion forces.
• The strength of London dispersion forces increases with the polarizability of the molecule, which in turn depends on the number of electrons and the surface area of the molecule.
• Larger and more flexible molecules have stronger dispersion forces.

Because of their ubiquitous nature, London dispersion forces are extremely important in the physical behavior of nonpolar substances.

Hydrogen Bonding

Hydrogen bonding is a special kind of dipole-dipole attraction that occurs when a hydrogen atom is covalently bonded to a highly electronegative atom such as fluorine, oxygen, or nitrogen, creating a strong dipole.

The positively charged hydrogen atom is attracted to a lone pair of electrons on a nearby electronegative atom in another molecule, forming a 'bridge' between them. This interaction is particularly strong compared to other dipole-dipole interactions due to the high polarity and small size of the hydrogen.

• Hydrogen bonding gives water its unique properties like high boiling point and surface tension.
• It is also responsible for the three-dimensional structure of proteins and nucleic acids in biology, making it essential to life as we know it.

Hydrogen bonding is not a bond in the classical sense but rather a very strong intermolecular force that plays a crucial role in the structure and interactions of molecules.

Ion-Induced Dipole Interaction

Ion-induced dipole interactions occur between ions and molecules that do not have a permanent dipole moment.

When an ion comes close to a nonpolar molecule, it can distort the electron cloud of the molecule, inducing a dipole. The strength of this interaction depends on several factors:

• The charge of the ion: Higher charge results in a stronger interaction.
• The polarizability of the nonpolar molecule: Molecules with greater polarizability have more easily distorted electron clouds, leading to stronger interactions.
• Distance between the ion and the nonpolar molecule: As with any electrostatic interaction, the closer the two are, the stronger the force.

These interactions are particularly significant because they contribute to the solubility of ionic substances in nonpolar solvents and influence many biological and chemical processes.