The relative strength of interionic/intermolecular forces in decreasing order is
(a) dipole-dipole

Q: Why is ion-ion considered an intermolecular force here?

Technically, ion-ion forces are 'interionic' rather than 'intermolecular' because they occur between ions, not molecules. However, in the context of comparing non-covalent electrostatic interactions that hold condensed phases together, they are often grouped in the same spectrum to illustrate the effect of charge magnitude.

Q: What exactly causes a partial charge in a dipole?

A partial charge is caused by a difference in electronegativity between two covalently bonded atoms. The more electronegative atom pulls the shared electron cloud closer to itself, gaining a slight negative charge ($\delta-$), while the other atom gets a slight positive charge ($\delta+$).

Q: Is hydrogen bonding stronger than ion-dipole interactions?

Generally, no. Hydrogen bonding is a very strong, specialized type of dipole-dipole interaction, but because it still relies on partial charges, it is typically weaker than an ion-dipole interaction, which involves at least one full formal charge.

Q: How does distance affect these different forces?

All these forces weaken as distance increases, but at different rates. Ion-ion forces drop off with the square of the distance ($1/r^2$), while ion-dipole forces drop off with the cube of the distance ($1/r^3$), and dipole-dipole forces drop off even faster ($1/r^6$ for rotating molecules).

Q: Can a single system have both ion-dipole and dipole-dipole forces?

Absolutely! A classic example is saltwater. The $\text{Na}^+$ and $\text{Cl}^-$ ions interact with water molecules via ion-dipole forces, while the water molecules simultaneously interact with each other via dipole-dipole forces (specifically, hydrogen bonding).

Question

The relative strength of interionic/intermolecular forces in decreasing order is

Options:

(A) dipole-dipole > ion-dipole > ion-ion

(B) ion-ion > ion-dipole > dipole-dipole

(C) ion-dipole > ion-ion > dipole-dipole

(D) ion-dipole > dipole-dipole > ion-ion

Sigma Percentile · Accepted Answer

### The Hierarchy of Electrostatic Forces

Imagine you are diving into the microscopic world of atoms and molecules. We are tasked with ranking three fundamental types of electrostatic interactions: **ion-ion**, **ion-dipole**, and **dipole-dipole**. The secret to unlocking this ranking lies entirely in understanding the magnitude of the electrical charges involved in each scenario.

### The Heavyweights: Ion-Ion Interactions

Let's start with the absolute heavyweights of the microscopic world: the **ion-ion interactions**. Think of a classic ionic compound like sodium chloride. Here, a complete transfer of electrons has occurred between the atoms. This complete transfer means the resulting particles possess full, integer formal charges, such as $+1$ for the sodium ion and $-1$ for the chloride ion.

According to Coulomb's law, the electrostatic force of attraction is directly proportional to the product of the magnitudes of the charges. Because ion-ion interactions involve full, complete charges, they generate a massive electrostatic pull. Therefore, ion-ion forces are unequivocally the strongest among the three types we are comparing.

### The Featherweights: Dipole-Dipole Interactions

Now, let's look at the other end of the spectrum: the **dipole-dipole interactions**. These forces occur between polar molecules, such as two molecules of hydrogen chloride ($	ext{HCl}$). In these molecules, electrons are not completely transferred; they are merely shared unequally due to differences in electronegativity.

This unequal sharing means the molecules only develop **partial charges**, which we denote as $\delta+$ and $\delta-$. Because these partial charges are just a small fraction of a full formal charge, the resulting attractive force between two dipoles is significantly weaker. They are the featherweights in our comparison.

### The Middle Ground: Ion-Dipole Interactions

Finally, we have the **ion-dipole interaction**. As the name beautifully suggests, it is a hybrid of the previous two. Picture a fully charged sodium ion ($	ext{Na}^+$) interacting with the partial negative charge ($\delta-$) of the oxygen atom in a water molecule.

In this scenario, you have one full charge interacting with one partial charge. Naturally, the strength of this interaction sits perfectly in the middle. It is weaker than the interaction between two full charges (ion-ion) but stronger than the interaction between two partial charges (dipole-dipole).

### The Final Verdict

Putting all the pieces of our puzzle together, the hierarchy is crystal clear. The complete charges of ion-ion make it the strongest, followed by the hybrid ion-dipole, and trailing at the end is the purely partial dipole-dipole interaction.

The correct decreasing order of relative strength is:

**$	ext{Ion-Ion} > 	ext{Ion-Dipole} > 	ext{Dipole-Dipole}$**

This is a fundamental concept that governs how substances dissolve, boil, and interact, making it a classic and high-yield topic for competitive exams.

Animated Solution for Chemistry - States of Matter: The relative strength of interionic/intermolecular forces in decreasing order is

Select Answer:

Visualized Solution

$T y p es o f I n t er a c t i o n s$

$I o n - I o n I n t er a c t i o n$

$D i p o l e - D i p o l e I n t er a c t i o n$

$I o n - D i p o l e I n t er a c t i o n$

$F ina l O r d er$

The Sigma Insight: Liquid State

The Hierarchy of Electrostatic Forces

The Heavyweights

The Featherweights

The Middle Ground

The Final Verdict

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