Intermolecular forces are attractive forces which attracted between molecules of a substance. it is an active forces that arise between molecules.

What is intermolecular forces?

Intermolecular forces are the forces which mediate attraction between molecules of a substance. Intermolecular forces is atractive forces thet arise between the molecules of a substance. it attract between partial negative end of one molecules to partial positive end of another molecules.

Physical and chemical property of the substance depend upon intermolecular forces. the boiling point of substance is proportion to the strength of intermolecular forces. IMF also mediate force of attractive and repulsion between molecules of a substance. this type of forces is intermolecular forces.

When stronger the intermolecular forces, then the higher the boiling point. this mean, higher the boiling point – stronger the (IMF). if the lower the boiling point, the weaker intermolecular forces.

According the above discussion, we can say that strength of intermolecular forces promotional to boiling point of a substance.

Here, we are going to discuss about intermolecular forces examples, such as NH3 (ammonia molecules) .

lets know with examples,

NH3, (Ammonia)

Yes, it is true, intermolecular forces occur between NH3 molecules, such as hydrogen bonding , dipole-dipole intraction and London dispersion forces. these type of intermolecular forces are may be strongest and may be weaker. hydrogen bond (strongest) and London dispersion forces (weaker) this type of intermolecular forces are persent between nh3 molecules.

lets konw in details with the help of structure,

According to structure of ammonia, three hydrogen atom are connected with one atom of nitrogen. elements has one loan pair. hydrogen are directly connected to nitrogen. this mean, hydrogen atom are conect with high electronegative atom (nitrogen) due to this hydrogen bond occur between this molecules.

NH3 molecules gives three different type of intermolecular forces, Such as, hydrogen bonding (strongest), dipole dipole intraction and london dispersion forces (weakest).

lets know in details,

NH3 molecules genrate hydrogen bonding. it one type of strongest intermolecular forces compare with all. In case of nh3, (N-H bonds are create between molecules). ammonia gives a dipole – dipole interaction (interaction between two dipole) and london dispersion forces also occur between nh3 molecules. there are three different types of intermolecular forces occur between nh3 molecules.

lets know, about all three different intermolecular forces which is occur between ammonia molecules with proper examples.

Hydrogen bonding (IMF)

According to ammonia structure, we can say that hydrogen atom are directly attached with high electronegative atom such as nitrogen (N). and we know that, if hydrogen bound to highly electronegative elements such as N, O, F. then they generate hydrogen bonds between two molecules. and bond create like – N-H, H-O, and H-F.

If hydrogen atom are directly connected with N, O, and F then it is make hydrogen bond between molecules. the best example is nh3 intermolecular forces. If we are talking about electronegativity, Nitrogen atom are highly electronegativity atom compare with hydrogen atom. so, due to large difference of electronegativity. negative charge is appear on nitrogen and positive charge is appear on hydrogen. due to this both atoms are attract each other. as a results, hydrogen bonds are generated between molecules.

According to difference in electronegativity between two atoms., suc as, N and H.

The value of electronegative of nitrogen is 3.0 and the value electronegative of hydrogen is 2.2. it mean nitrogen has highly electronegative atoms compare with hydrogen. the difference of electronegativity between atoms is (0.8).

Therefore, the large difference in electronegativity between the N atom and H atom, N-O, N-F atoms leads to highly polar covalent bond. so, it mention this is polar molecules. and this molecules (nh3) generated hydrogen bonding.

If Hydrogen atom attached to an element with high electronegative atom such as, N, O, F. then hydrogen bond are genreated. but in case of ammonia ,this molecule has one loan pair.

As a result, this molecules is called highly polarized molecules. in this case, partial positive charge appear on hydrogen and partial negative chare appear on nitrogen. there are two highly polarized molecules. and both are attract each other. partial positive charge of hydrogen are attracted with partial negative charge of other molecules. As a result attraction forces is produced between them. this type of forces is called hydrogen bonding. hydrogen bonding is also called intermolecular forces between two molecules.

the intermolecular forces

Hydrogen bonds also occur between hydrogen fluoride molecules. and atmos are bound to highly electronegative elements. and it has available loan pair electron. therefore, it is more possibility to make hydrogen bonding.

Dipole – Dipole interaction (IMF)

Dipole-dipole intraction are attracted among polarized molecules. this mean, dipole dipole forces exist between polar molecules.and if molecules have electric dipole.

We know that polarized molecules has two poles partial positive pole and partial negative pole. therefore it is called dipole. and dipole dipole intraction occur between two polarized dipole.

For examples,

NH3, HCl, HF, H2O

these types of molecules are polar in nature. dipole dipole interaction exist between polar molecules. so, dipole dipole interaction occur on polarized molecules. first take HCl molecules. how this molecules create dipole dipole interaction.

it has two pole partial positive pole and partial negative poles. consider another dipole it has also two poles, partial positive pole and partial negative poles, we has two dipoles. So, the negative pole of one molecules attracted the positive pole of another molecules. due to this attractive forces are produces. this attractive forces is called dipole dipole intraction.

Now take another examples, like HF molecules, this molecules are also genrate dipole dipole interaction.

Similarly, consider the single molecules of hydrogen fluoride. you know that it is dipole because it has two pole partial positive pole and partial negative pole.

Consider another molecules of hydrogen fluoride, these are also a dipole because it has two pole partial positive pole and partial negative pole.

The negative pole of one molecules attracted to positive pole of another molecules. due to this attractive forces produced between two dipoles, this type of forces is called dipole-dipole intraction

London dispersion forces (IMF)

London dispersion forces mainly occur non polar molecules. so, this forces exist between non polar molecules. this mean, the molecules should be a non polar then it is only intermolecular forces is the london dispersion forces. and this (LDF) are as weakest intermolecular forces.

london dispersion forces is not operate long distance, it is oprate short distance. it create temporary positive to temporary negative charged. london dispersion forces is a weak force compare with dipole-dipole intraction Or hydrogen bond.

Ammonia molecules are polar in nature. so, Nitrogen are high electronegative atom compared with hydrogen atom. due to this nitrogen create partial negative charge and hydrogen create partial positive charge and then attracted each other.

As a results, when one ammonia molecules attracted with another, it genrate all intermolecular forces are involved such as, hydrogen bond, dipole dipole interaction, and london dispersion forces.

Types of Intermolecular forces

1. Dipole – dipole interaction

Dipole dipole interaction is one type attractive forces among polar molecules. dipole dipole forces occur if molecules have electric dipole (+ charge or – charge).

The partial positive end of one molecules is attracted to the partial negative end of another molecules.

So, this forces are refer force of attraction between two polar molecules. it attracted between one positive dipole to another negative dipole.

So, we can say that, dipole dipole interaction occur between two dipole, one dipole should be positive and anther should be negative..

For examples,

HCl

Dipole dipole interaction occur in polar molecules. HCl are polar molecules. it attracted between positive end of one molecules to negative end of another molecules.

types of intermolecular forces

In case of HCl, Cl is high electronegative atom compare with hydrogen. Due to this, Cl appear negative charge whereas hydrogen appear positive charge.

Dipole dipole interaction between positive portion of one molecules to negative portion of another molecules. dipole dipole interaction then take place in HCl.

2. Ion – dipole interaction

Ion dipole interaction occur between ion and dipole. it is similar as dipole dipole interaction.

When NaCl mixed with water molecules then water are attracted with NaCl.

were,

H2O – polar molecules

NaCl – ion

They attracted between ion (NaCl) and dipole (H2O). Let’s know with structure.

ion dipole interaction

3. Ion induced dipole interaction

This type of intraction forces is persent between an ion and non polar molecules. this mean, intraction between ion and non polar molecules.

An non polar molecules can be polarized by the presence of ion.

for examples,

H2 , I2

lets know with structure

Ion induced dipole interaction

4. Dipole induced dipole interaction

This type of forces exist between polar and non polar (atoms & molecules).

Polar – In polar molecules, electrons are distributed Unsymmetrically. they have permanent electric dipole (charge). polar molecules have two equal opposite charge. this mean, it genrate two pole one is positive and another is negative. this is know as polar molecules.

for examples,

HCl, NH3, HF, H2O and more

Non polar – electrons are distributed symmetrically. but they don’t have electric dipole. this mean there is no any pole. there is no any intraction is possible. this is known as non polar.

for examples,

He, Ar, Ne & more

In case of dipole induced dipole interaction, this interaction occur between polar and non polar is,

HCl – polar

He – non polar

lets know examples,

Here, we will discuss about intraction between polar (HCl) and non polar (He).

dipole induced dipole interaction

5. London dispersion forces

This type of forces are interacted due to movement of electrons this create temporary positive charge and negative charge. they are interacted between instantaneous dipole and induced dipole as shown in figure.

london dispersion forces

According to chemistry point of view, this type of forces is exist between non polar atom and molecules.

Non polar – electrons distributed symmetrically, they don’t have any electric charge. there is no any dipole to interaction of one molecules to another.

for examples,

Forces – H2, O2, F2,

Nobel gass – He, Ne, Ar,

Question And Answers

1. Intermolecular forces on liquid are?

(a) Weaker then in solids

(b) stronger then in solids

(c) Weaker then in gases

(d) As stronger as in solids

Intermolecular forces on liquid are weaker then in solids. this mean, intermolecular forces are greter on solids compare on liquid.

So, due to this, option (a) is correct.

2. What are the intermolecular forces strongest to weakest?

In intermolecular forces point of view, the proper sequence of strongest intermolecular forces and weakest intermolecular forces are,

(a) Ion dipole forces

(b) Hydrogen bonding

(c) Dipole – dipole forces

(d) Van der waals forces

These are the properly sequence for strongest to weakest intermolecular forces.

3. Identify the intermolecular forces persent in each of these substance?

(a) H2O

(b) He

(c) CH3Cl

(d) CO

Answer

Actually, the intermolecular forces are the attractive forces. and it occur between molecules. different molecules genrate different intermolecular forces such as, dipole dipole interaction, hydrogen bonding, London dispersion forces, and ion dipole interaction. these type of intermolecular forces occur between molecules. If in molecules hydrogen are bound to N, O, F then hydrogen bond are persent in molecules.

For example

H2O – in this molecules, hydrogen are directly connected to Oxygen and dipole dipole interaction, hydrogen bonding and ion dipole interaction occur between molecules.

He – this is non polar molecules, there is no any dipole to intract to each other, so London dispersion forces occur between molecules.

CH3Cl – Dipole dipole forces and London dispersion forces are persent ch3cl molecules.

Co – this is polar molecules, so has dipole dipole interaction, van der waals forces are persent between molecules.

So the above discussion, Option (a) is correct.

4. What happens to these physical properties as the strength of intermolecular forces increases?

The physical properties as the Intermolecular forces are attractive forces which attracted between molecules of a substance.

We know that, the strength of intermolecular forces as increases then higher the boiling point, melting point and more. this is depends upon strength of intermolecular forces and also depends upon molecules.


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