Different Types of Intermolecular Forces

Introduction

Intermolecular Forces are the forces that serve as the foundation for all interactions between molecules. These interactions are less powerful than intramolecular forces. The intensity of the intermolecular forces (IMF) of attraction dictates the sort of interaction that will occur between 2 molecules, as well as the alterations that these interactions will cause. When considering Intermolecular forces (IMF) of attraction, the most typical reference is a water $\mathrm{(H_{2}O)}$ molecule. Intermolecular forces (IMF) govern the physical characteristics of matter. Furthermore, water ($\mathrm{(H_{2}O)}$) is 1 of the few compounds that can exist in all 3 states: solid, liquid, as well as gaseous.

What are Intermolecular Forces ?

The word "intermolecular forces (IMF)" denotes the electrostatic forces (EF) of attraction and even repulsion between atoms since the adjective "inter" implies “between”. Another word for the forces that exist between atoms to form molecules is 'intramolecular forces.' E.g., the terms 'international' and 'international' refer to interactions between 2 or more nations, respectively. Intermolecular forces (IMF) are the forces that are present between atoms. These forces include dipole-dipole(d-d) interactions, ion-dipole (I-d) interactions, ion-induced dipole (I-Id) interactions, van der Waals forces (VDW), including hydrogen (𝐻) bonding. These forces are required to compute the physical characteristics of substances such as density, enthalpies, melting point (M.P.), boiling point (B.P.), vaporisation, and so on. IMF are far weaker than intramolecular forces, such as ionic or covalent bonds.

What are Different Types of Intermolecular Forces

They are broadly classified into 3 types − van der Waals (VDW) forces, dipole-to-dipole (d-d) interactions, as well as hydrogen bonding. However, the phrase induced dipoles, which refers to London dispersion forces (LDF), is further classified. This results in 5 different forms of intermolecular forces (IMF).

• Dipole-dipole forces (d-d forces)

• Ion-dipole interaction (I-d interaction)

• Ion-induced dipole interaction (I-Id interaction)

• Van der Waal forces

• Hydrogen bonding

Dipole-Dipole Interaction

The partly +ve as well as -ve sides between compounds cause this type of interaction. The -ve side of a molecule attracts the +ve side of other molecules, resulting in the formation of Electrostatic Forces (EF) of attraction referred to as dipole-dipole interaction between molecules. This type of electrostatic attraction is weaker than that of ion-to-ion contact. Since dipole interactions are based on partial charges, ionic interactions are based on permanent +ve as well as -ve charges known as cations, including anions respectively.

Hydrochloric acid $\mathrm{(HCl)}$ interactions are instances of dipole-dipole forces. The 𝐻 atom is partially +ve, whereas the 𝐶𝑙 atom is partially -ve. When a partially -ve 𝐶𝑙 atom draws partially positive hydrogen (𝐻) from neighbouring molecules, a large network of similar connections is generated. Hydrogen disulfide $\mathrm{(H_{2}S)}$, nitrogen dioxide $\mathrm{(NO_{2})}$ , water $\mathrm{(H_{2}O)}$, sulphur dioxide $\mathrm{(SO_{2})}$, EDTA (Ethylene diamine tetraacetic acid), ammonia $\mathrm{(NH_{3})}$, and other polar molecules are the only ones that can interact dipole to dipole. These interactions are influenced by the characteristics of polar molecules.

Ion-Dipole Interaction

These interactions arise when ions plus polar compounds engage as well as form an interacting force. Polar molecules have partial positive as well as negative charges, so when an ion with a +ve or -ve charge approaches them, an electrostatic force (EF) is established among them. Because opposing charges repel while similar charges attract, an ion is always attracted to the oppositely charged end of a polar compound.

Water $\mathrm{(H_{2}O)}$ molecules combine with sodium ions plus chloride ions when sodium chloride $\mathrm{(NaCl)}$ is introduced to it. Water's ability to split ionic substances into ions via ion-dipole interactions is known as hydration.

Ion-Induced Dipole Interaction

Ions oversee ion-induced interactions. Whenever an ion contacts a non-polar substance, it causes the substance to generate partial +ve as well as -ve poles, transforming it to a dipolar configuration. In other terms, an ion creates a dipole moment on non-polar molecules, causing them to become polar molecules. Metal ions approaching oxygen (𝑂) and other molecules & causing a net dipole moment in them are cases of such interactions.

If ions are used to produce dipoles, the resulting forces are known as ion-induced dipole interaction. However, if these interactions occur between existing polar molecules and non-polar molecules, they are referred to as dipole-induced dipole interactions. Examples $\mathrm{(NO^{-})}$,

Conclusion

IMF are the forces of attraction as well as repulsion that exist between a substance. They are electrostatic forces that exist between molecules including atoms. The boiling point (B.P.) of various substances is related to their intermolecular forces (IMF). The weakest forces are the London forces or dispersion forces. Like dipole-dipole interactions, ion-dipole interactions occur between ions plus polar atoms.

FAQs

1. Why does the viscosity of liquids decrease with increasing temperature?

So that at high temperatures, the molecules of a substance gain high kinetic energy but may overcome intermolecular interactions to glide over 1 another between the layers, and the viscosity of liquids reduces.

2. The magnitude of a crystal's melting point (M.P.) reflects its stability. Explain?

The melting point (M.P) of a solid describes the intermolecular forces that operate between a substance's components. When these forces are significant, the m.p. of the component is greater; when these forces are low, the m.p. of the component is low. The higher the m.p. of a solid, the more stable it is.

3. In the molten state or aqueous solutions, ionic solids are good conductors, but not in the solid form. Why?

The ions of an ionic solid do not freely travel in the solid state due to the stiff structure plus high electrostatic force. Therefore, they can never conduct electricity while molten, but in an aqueous solution, the ions freely travel and thus conduct electricity.

4. What are the forces that contribute to a liquid's viscosity? What causes glycerol to be more viscous than water $\mathrm{(H_{2}O)}$ ?

The forces responsible for a liquid's viscosity include hydrogen (𝐻) bonding as well as Van der Waals (VDW) forces. Glycerol is much more viscous than water $\mathrm{(H_{2}O)}$ because the atoms of glycerol have a little more hydrogen bonding owing to the pressure of 3 oil groups in it than the compounds of water $\mathrm{(H_{2}O)}$.

5. The size of a crystal's melting point (M.P.) reflects its stability. Using a data book, collect the melting points (M.P.) of solid water, ethyl alcohol, diethyl ether, as well as methane. What could be said about these molecules' intermolecular forces (IMF)?

The higher the melting point (M.P.) of something like a material, the stronger its intermolecular force of attraction as well as the better its stability. A higher melting point (M.P.) material is more stable than a low melting point (M.P.) component.

$\mathrm{Diethyl\:ether\:=\:-116.3°C}$

$\mathrm{Methane\:=\:-183.81°C}$

$\mathrm{Solid\:water\:=\:-0.15°C}$

$\mathrm{Ethyl\:alcohol\:=\:-114.35°C}$

The intermolecular forces (IMF) in solid water are the highest, while those in methane are the least, based on the values of the provided components.