What are intermolecular forces?

The intermolecular forces are the forces which mediate attraction between two molecules in a substance. this forces are also mediate force of attraction and repulsion between molecules of a substance. but different molecules form different types of intermolecular forces. it is depends upon molecules. it attract between partial negative end of one molecules to partial positive end of another molecules. this is called intermolecular forces.

For example;

NH3 Ammonia has stronger intermolecular forces.

CH3OH has also stronger intermolecular forces. but helium has weaker intermolecular forces.


Types of intermolecular forces

Intermolecular forces is an attractive forces, that is occur between molecules. it attract from the partial positive portion of one molecules into partial negative portion of another molecules. the basic concepts of intermolecular forces is, it is an attractive forces, and this forces mainly occur between two molecules. but different molecules has different types of intermolecular forces.

Lets know with example,

Yes, nh3 molecules has stronger intermolecular forces whereas helium has week intermolecular forces. ch3oh molecules has stronger intermolecular forces whereas Ne has weaker intermolecular forces. different types of intermolecular forces is depends upon molecules. but the physical and chemical properties of a substance are depends upon forces. and if we are taking about boiling point then, the basic concepts of boiling point of strength of intermolecular forces is, boiling point is proportional to the strength of it’s intermolecular forces. This mean, If stronger the intermolecular forces then higher the boiling point.

Stronger intermolecular forces – higher boiling point

For example,

HCl (stronger IMF) – higher boiling point

H2O (stronger IMF) – higher boiling point

According to this, we can say that different substance have different boiling point and also different strength of intermolecular forces. because the heat absorbed by the substance at its boiling point is used to break these intermolecular forces and to convert the liquid into vapour.

Intermolecular forces depends on the following interaction.

Lets know in details about different types of intermolecular forces.

  1. Dipole – Dipole interaction
  2. Ion – Dipole interaction
  3. Ion induced Dipole interaction
  4. Dipole induced dipole interaction
  5. Dispersion forces or London dispersion forces.

1. Dipole – Dipole interaction

Dipole – dipole interaction are one type of attractive forces.

Yes, it is true this type of interaction formed on polar molecules. dipole – dipole interaction are mainly occur on permanent dipoles.

This mean, polar molecules have permanent dipoles that are formed due to difference in electronegative of the atoms that ate associated with covalent bonds.

Dut to this, the partial positive portion of one molecules is attracted to the partial negative portion of another molecules.

This interaction occur between two poles, one poles are partial positive and another are partial negative.

For example;

1. NH3

Yes, stronger Intermolecular forces occur between nh3 molecules. the intermolecular forces in nh3 are hydrogen bonding, dipole dipole intraction, and london dispersion forces. It make N-H bonds. in this molecules, hydrogen are directly connected with nitrogen but nitrogen has highly electronegative value. so, large difference of electronegativity between nitrogen and hydrogen. due to this, partial negative charge appear on nitrogen and partial positive charge appear on hydrogen. due to this it attract each other.

As a result, we can sya that, the intermolecular forces of nh3 is hydrogen bonding, dipole-dipole and london dispersion forces. this type of forces occur between nh3 molecules. this type of intermolecular forces are called stronger intermolecular forces.

Hydrogen bonding

Yes, hydrogen bonding occur between nh3 molecules because if you look at the structure of nh3, hydrogen are directly attached with high electronegative atom such as Nitrogen. We know that, if any molecules bound to highly electronegative elements then they generate hydrogen bonds between two molecules such as, N-H, H-O, and H-F then it makes hydrogen bond between molecules.

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. and due to this attraction hydrogen bonds are generated between molecules.

Due to this reson, nh3 molecules are a polar molecules but if any body may asked with you that nh3 polar or nonpolar then you can say that yes, nh3 is polar molecules, this is because nh3 molecules has two pole due to this it attract each other.

Another reason is, According to difference in electronegativity between two atoms., suc as, N and H. you know that, 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, you can say that, polar molecules generated hydrogen bonding.

Lets know with example,

Hydrogen attached to an element with high electronegative atom such as, N, O, F.

such as,

H-N, H-O, H-F

Elements has atleast one loan pair.

Due to 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 nitrogen molecules.

As a result attraction forces is produced between them. this type of interaction is called hydrogen bonding.

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.

2. CH3OH

The intermolecular forces in ch3oh are, hydrogen bonding, dipole dipole intraction, and london dispersion forces.

Lets know in details, how to this type of intraction occur between ch3oh molecules.

Hydrogen bonding

types of intermolecular forces

Yes, hydrogen bonding is present between two methanol molecules. because oxygen is directly attached to hydrogen and due to this reason hydrogen bonding occur between molecules. it is strong intermolecular forces occur between oxygen and hydrogen. You know that oxygen is highly electronegativity atoms compare with hydrogen. according to this, oxygen has partial negative charge whereas hydrogen has partial positive charge. according to this, both atoms are attracted each other.

As a results, hydrogen bonding occur between this two molecule.

Now, You can understand properly with the help of chemical structure.

The chemical structure gives proper understanding.

Lets know in details,

Dipole dipole intraction

dipole dipole intraction

Yes, dipole-dipole interaction occur in methanol because it creat dipole moment between molecules due to the presence of the electronegative oxygen atom.

The electronegative atom which is oxygen that create a permanent positive charge on the molecules and rest of the molecules create partial negative charge . and that create parmanent dipole within each of the methanol molecules with opposing charge. this type of interaction is called dipole-dipole interaction.

London dispersion forces

Yes, it is absolutely true, methanol are also generate london dispersion forces between two non polar molecules. the basic concepts is this that, the interaction between two non polar methanol molecules. it mean, one hydrogen atom of first methanol interacted with second hydrogen of second methanol molecules. But It generated very weak intermolecular forces. In other words, there is not any poles to interact each other. this is one type of interaction between two methanol molecules in which very weak intermolecular forces are generated. this weak interaction is know as London dispersion forces. this is shown in figure.

This type of interaction created between non polar molecules. this type of force is called london dispersion forces. So, we can say that, ch3oh intermolecular forces has also London dispersion forces.

2. Ion dipole interaction

These interactions are similar to dipole-dipole interactions. this type of interaction occur between ions and polar molecules.

 For example;

When NaCl is mixed with water in a beaker, the polar H2O molecules are attracted to the sodium and chloride ions in the beaker.

The strength of this interaction depends on magnitude, size of polar molecules, size and charge of ion.

3. Ion induced dipole interaction

Ion induced dipole interaction occur between an ion and induced dipole.

Actually, the basic concepts of ion induced dipole interaction is, A nonpolar molecules is polarized by an ion placed near it.

Due to this concept, it obtained charge like induced dipole.

This type of interaction is known as ion induced dipole interaction.

4. Dipole induced dipole interaction

This type of interaction is also same as ion induced dipole interaction.

In this case, An nonpolar molecules are formed induced dipole, polar molecules by an ion.

This concept is same as ion induced dipole interaction.

In dipole induced dipole interaction, nonpolar molecules are converted to induced dipole and polarized by an ion.

5. London dispersion forces

London dispersion forces is know as temporary dipole. there is no any permanent poles to attract each other. this mean, there is no any positive poles and there is no any negative pole to attract each other.

Due to this, there is not possible for dipole – dipole interaction and there is not possible to make hydrogen bond.

Due to this concept, the formation of temporary dipole the movement in electrons density between molecules.

it is aslo known as induced dipole – dipole interaction. london dispersion forces is known as a week forces.

For example

Xe (Xenon) ;

Yes, Helium is one type of noble gas elements. helium has no any attractive forces. this mean, there are no any attractive forces exist in helium.

helium has no any attractive tendency because there is any dipole for attraction. No dipole, this mean, no dipole dipole intraction.

So, no attraction means, due to this, it is called week intermolecular forces.

Helium has london dispersion forces which is the weakest intermolecular forces whereas hydrogen bond and dipole dipole intraction are stronger intermolecular forces.


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