Intermolecular Interactions

Have you ever wondered why solids are so strong and liquids flow so freely? How are we able to liquefy gases? We must first study intermolecular interactions to comprehend these notions. So, what are intermolecular forces and, more specifically, what are intermolecular interactions? Solids are strong, and liquids flow because of the forces of attraction between solids and liquids. The electrostatic forces between the molecule and the atoms are called intermolecular forces of attraction.

Atoms and molecules make up everything that surrounds us. A force of attraction or repulsion exists between atoms and molecules at all times. The molecule’s properties are determined by the forces that exist within it. Now let’s look at the types of intermolecular interactions.

Intermolecular forces refer to the forces that hold molecules together. Although the energy necessary to tear molecules apart is far lower than that required to break a conventional bond, intermolecular forces play an essential role in determining a substance’s qualities. Intermolecular forces are crucial in combining molecules and forming biological creatures or even life. Now let us learn in detail about intermolecular interactions.

Types of intermolecular forces

Dipole-dipole interactions

When a molecule’s partially positively charged component interacts with an adjacent molecule’s partially negatively charged region, these forces are produced. Partially charged ions are required for this form of attraction to exist. The most vital intermolecular force of attraction is dipole-dipole interactions, like in the case of polar covalent bonds like hydrogen chloride. For example, HCl provides the best intermolecular forces for a dipole-dipole interaction. The negative charge of chlorine is opposite the positive charge of hydrogen in HCl. Dipole-dipole forces are created by the attraction forces between two negative charges. The polarity of the molecules can predict the magnitude of these forces.

Ion – Dipole Interaction

The ion-dipole interaction resembles the dipole-dipole interaction pretty closely. The only difference is that the bonds are formed between ions and polar molecules rather than between polar molecules and ions.

Consider the molecule of sodium chloride as an example. When NaCl is dissolved in water, polar molecules form in the H₂0, attracted to Cl- and Na+ ions. The strength of the forces between them is determined by the polar molecule’s size and the dipole moment’s strength.

Ion Induced Dipole Interaction

When an ion comes close to a nonpolar molecule, it can polarise it. Due to the presence of an ion, the nonpolar molecule forms an induced dipole. An ion-induced dipole interaction occurs when an ion interacts with a nonpolar molecule. The strength of intermolecular forces is usually determined by how easily a nonpolar molecule may be polarised.

Dipole Induced Dipole Interaction

Ion-induced dipole interactions are analogous to these interactions. The difference is that nonpolar molecules are turned into induced dipoles when a polar molecule is present nearby.

Van der Waals force or London dispersion forces

 In any substance, these forces are always at work. The induced dipole interaction produces a weaker force than the dipole-dipole interaction. In general, the stronger the van der Waal force of interaction, the heavier the molecule. Because of higher London dispersion interactions, the boiling points of inert gases rise as their atomic masses rise.

Electrostatic forces attract water molecules in liquid water, and these forces have been referred to as van der Waals forces or London dispersion forces. Van der Waals bonding is exemplified by hydrogen bonding, which is crucial to the characteristics of water and its behaviour in biochemistry.

Hydrogen Bonding

When a hydrogen atom connected to a strongly electronegative atom is in the neighbourhood of another electronegative atom with a lone pair of electrons, it creates a specific sort of dipole-dipole attraction called a hydrogen bond. An example of intermolecular hydrogen bonding range from tiny molecules like CH₃NH₂ to giant molecules like proteins and DNA; there’s something for everyone.

Role of intermolecular interactions in the states of matter

• Conflict in London Forces attracts all atoms and molecules to each other.
• An uneven electron distribution can cause temporary dipoles in particles. This pair of transient dipoles are attracted to each other. Large, polarisable molecules have the strongest of these forces. Dipole forces result from the attraction between molecules’ positive and negative ends with permanent dipoles.
• A massive dipole is formed when a hydrogen atom is covalently attached to a strongly electronegative atom (N, O, F). As a result, even the tiniest molecules have strong intermolecular connections.

Properties affected by Intermolecular interactions-

Strength: The strength of the attractions between particles can significantly affect the properties of a substance or solution. 

Viscosity:  The viscosity of a liquid is its resistance to flow. It has something to do with how easily molecules can pass each other. Viscosity rises as intermolecular forces get stronger and falls as temperature rises.

Surface tension: Surface Tension results from the net inward force experienced by the molecules on the surface of a liquid.

Conclusion

Intermolecular forces are substantially less than intramolecular attraction forces. Yet, they are crucial because they determine the physical properties of molecules such as boiling point, melting temperature, density, and fusion and vaporisation enthalpies. These properties are fundamental to understanding the compound. Intermolecular interactions have an impact on the boiling and freezing points of substances. The boiling and freezing points of substances increase as intermolecular tensions increase. The boiling and freezing points are lower when intermolecular forces are low. It also impacts the liquid’s fluidity; the stronger the forces, the slower the liquid moves.