Question

(a) Which type of intermolecular attractive force operates between all molecules? (b) Which type of intermolecular attractive force operates only between polar molecules? (c) Which type of intermolecular attractive force operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom?

Short answer

(a) The intermolecular attractive force that operates between all molecules is "London dispersion forces" or "van der Waals forces". (b) The intermolecular attractive force that operates only between polar molecules is called "dipole-dipole interactions". (c) The intermolecular attractive force that operates between the hydrogen atom of a polar bond and a nearby small electronegative atom is called "hydrogen bonding".

Step-by-step solution

(a) Type of force that operates between all molecules:

The intermolecular attractive force that operates between all molecules, regardless of their polarity or type, is called "London dispersion forces" or "van der Waals forces". These forces arise due to temporary fluctuations in electron distribution around molecules, which create temporary dipoles that induce dipoles in nearby molecules.

(b) Type of force that operates only between polar molecules:

The intermolecular attractive force that operates only between polar molecules is called "dipole-dipole interactions". These forces occur when the positive end (partial positive charge) of one polar molecule interacts with the negative end (partial negative charge) of another polar molecule.

(c) Type of force that operates between the hydrogen atom of a polar bond and a nearby small electronegative atom:

The intermolecular attractive force that operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom (such as fluorine, oxygen, or nitrogen) is called "hydrogen bonding". This is a special case of dipole-dipole interaction, where the hydrogen atom forms a particularly strong interaction with the nearby electronegative atom due to the significant difference in electronegativity between them.

Key concepts

London Dispersion Forces

London dispersion forces are a type of intermolecular force that exist in every molecule. You might think of them as the "universal glue" that has an effect on all matter, regardless of whether the molecules are polar or non-polar. This force arises from temporary shifts in the electron clouds of atoms.
When these electrons shift, they create temporary dipoles. These are brief moments where there is a slight imbalance of charge within the molecule. Imagine a tiny light switch flickering on and off, causing these dipoles to appear and disappear rapidly.
As these temporary dipoles form, they shift electrons in neighboring molecules, inducing dipoles there as well. This action creates London dispersion forces, or "van der Waals forces," which might seem weak but in large numbers, they greatly influence the properties of substances, such as boiling and melting points.

• These forces increase with higher molecular size and mass, making larger molecules stickier.
• Their universality means they're an important concept for understanding chemistry basics.

Dipole-Dipole Interactions

Dipole-dipole interactions are a type of intermolecular force unique to polar molecules. Think of them as the magnetic bonding of the molecular world. Polar molecules have a distinct positive charge on one side and a negative charge on the other, like a small bar magnet.
These charges do not happen by accident. Instead, they occur because one part of the molecule pulls harder on shared electrons, creating a dipole. The positively charged end of one molecule will naturally attract the negatively charged end of another. This attraction creates dipole-dipole interactions.
The strength of these forces means they have a significant impact on the physical properties of substances.

• They are stronger than London dispersion forces because the dipoles are permanent.
• Their influence includes higher boiling points and solubility in polar environments.

While dipole-dipole interactions are limited to a certain kind of molecule, they play a crucial role in molecular interactions.

Hydrogen Bonding

Hydrogen bonding is a particular type of intermolecular force, and it's in a league of its own due to its strength and specificity. Picture it as the "VIP section" of intermolecular forces, operating under stringent conditions.
This force occurs between a hydrogen atom in a polar bond and a nearby small electronegative atom, like fluorine, oxygen, or nitrogen. The substantial difference in electronegativity draws the hydrogen quite close, creating a very strong interaction.
This type of bonding is notably stronger than typical dipole-dipole interactions due to the polar bond's strength and the lack of shielding of hydrogen's nucleus.

• It's crucial in maintaining the structure of water, leading to properties like surface tension and ice buoyancy.
• It's fundamental in biological structures, such as DNA and proteins.

Understanding hydrogen bonding provides insights into many biochemical and physical processes, illustrating the critical role it plays in life as we know it.