Hello, reders Welcome to chemwhite.com, today we will discuss about London dispersion forces and also cover it’s examples, types, and factor effecting.

lets get started,

Defination

London dispersion forces is one type of weakest intermolecular forces. It occur between all atoms or molecules when it touch in each other.

London dispersion forces

A german physicist who developed this forces like, “intermolecular forces”. basically, the intermolecular force of attraction occur between atoms & molecules, when it is come in contact each other. there are different types of intermolecular such as, london dispersion forces, hydrogen bond, dipole-dipole intraction, and the ion ion intraction. but here, we will discuss about LDF, LDF is made weak intermolecular forces when they attracted between molecules.

The force of attraction between instant dipole (temporary dipole) and induced dipole is called london dispersion forces. it is also called temporary attractive force because it is made temporary dipole in a non polar molecules. you know that, all the matter is made-up from atoms. and if the different atoms are combine each other it form molecules. intermolecular forces of attraction occur between atoms or molecules. but here we will discuss about how to form LDF, after attracted between two molecules.

LDF, is made temporary dipole in a non polar molecules. it is mainly occur between temporary dipole and induced dipole. When non polar atoms or molecules contact each other due to this they creat force of attraction between them. it is called LDF. the force of atraction between temporary dipole and induce dipole is also called london dispersion forces. it is present between any of them. and it is a weak intermolecular forces compair with hydrogen bond, dipole-dipole intraction, ion ion force. london dispersion forces is made temporary attractive force between molecules.

temporary dipole – temporary dipole is a dipole when the electronic cloud of of neutral atom is distorted for a time being. it has temporary positive pole and temporary negative pole.

induce dipole – this is the intraction between polar molecules having a parmanent dipole moment. polar molecules having partial positive charge and parial negative charge. And if I m talki g about a non polar molecule. the main concept of non polar molecules is, non polar molecules has zero dipole moment. non polar molecules which has no pole. it mean there is no pole neither positive nor negative.

When temporary dipole contact with neutral atoms then the positive pole of temporary dipole will attracted easily (pull the electron) the electronic cloud of this neutral atom. As a result, the structure of neutral atom will distorted, you can understand properly with the following structure.

Interaction between temporary dipole and neutral dipole.

In distorted neutral atom, one side of neutral atom has more electron (appear negative pole) and another side is less electron (appear positive pole). this type of dipole is called induced dipole. because the temporary dipole will change the arrangement of electron in neutral atom.

London dispersion force mainly occur between two polarized dipole such as, temporary dipole and induced dipole.

When the positive end of temporary dipole is attracted negative end of induced dipole, this types of attraction between two polarized molecules is called LDF. this force is also called van der waals forces. but LDF is a weak forces and temporary forces of attraction.

for example – CH4

Methane (Ch4) is best examples of London dispersion forces Methane has only London dispersion forces. Methane is a non polar molecules. due to this there is no pole, either positive or neither negative.

Temporary dipole formation

Basic concepts – First you look in digram, first atom having symmetric distribution of electron time come this electron move towards the one side of the atom. Where as, neucle move towards because unsymmetrical distribution of electron. As a result temporary dipole is formed.

Temporary dipole formation
Temporary dipole formation

you know that, it is formed very short period of time, as a result, this type of dipole is formed, it produce parial positive pole and partial negative pole. it is given below.

But when temporary dipole come in contact with symmetrical atoms,

Temporary dipole formation

electron cloud repale the electrons cloud of the symmetrical. as a result induced dipole is formed. LDF is also called dipole induce dipole force. you can understand above information with the help of digram.

Temporary dipole formation

this dipole is called induce dipole. and this intraction is called dipole induce dipole forces.

Types of Bonds

1. Ionic bonds

For examples;

(a) Sodium chloride (NaCl)

In this case, sodium loses one electron to form Na+ ion. If electron transfer to chlorine to form a cl- ion.

Due to this, it form Na+ ion and Cl – ion.

They are Oppositievly charge iona and will be Electrostatically attracted to one another. and the opposite poles of the magnet are attracted to one another.

As a result, this electrostatic attraction is an ionic bonds. As shown on structure.

(b) KCl

The same think happen, with kcl and resulting an ionic bonds are formed.

2. Covalent bonds

There are many examples, such as Cl2, H2, H2O ate represent covalent bonds. covalent compound are the compound which are formed by sharing of electrons. this iss known as covalent bonds.

Lets know, with examples, it is clear with structure.

1. Cl2,

covalent bonds

3. Cordinate bonds

Cordinate bond is stabilished between two such atoms. On of which has complete octet. and posses a pair of valence electrons. while the other is short of a pair of electrons.

for examples;

1. NH3 (Ammonia)

cordinate bonds

2. NO3

London dispersion forces

3. H3O-

cordinate bond

4. H2O

4. Hydrogen bonds

For examples,

1. HF

An attraction between partial positive to partial negative and make an hydrogen bonds as shown on HF structure. this type attraction between molecules is known as hydrogen bonds.

Here, we will show different examples to represent hydrogen bond.

hydrogen bond

3. H2O

An attractive force is know as hydrogen bond can be exist between certain molecules.

You know, hydrogen bond are less weaker then ionic bond or covalent bond. reson is it takes less energy to break.

Yes, this is absolutely true, this types of bonds required less energy to break down.

Hydrogen bonds are the results of an unequal charge distribution on a molecules (polar molecules).

In this case, 2 (shared of electrons) between the oxygen atom and hydrogen atom – 1,

2 shared between oxygen atom and hydrogen atom – 2.

As shown in structure.,

hydrogen bond

The other 6 non shared electrons from the oxygen atom.

it has partial positive side , the hydrogen side and a partial negative charge, the oxygen side of molecules.

It attraction between positive (+) and negative (-). due to this it make hydrogen bonds.

5. Metallic bonds

Metallic bond is a type of chemical bonding. metallic bond are formed from electrostatic attractive force between electrons and positive charge metal ion.

There are many examples represent metallic bonds such as,

Fe, Cu, Zn

Metallic bond are formed due to making bond between electrons and metal ions because electron has – negative charge and metal has positive charge. this is one type of electrostatic attractive between electrons and metal ions. this bond is known as metallic bond.

London dispersion forces examples

Basic concepts – you know that, chlorine atom is best example for london dispersion forces, LDF is present in every chemical. such as “chlorine”. LDF is mostly attract in non polar molecules. because Chlorine is also a non polar molecules.

LDF is present when two atoms close to each other due to this induced dipole is formed in atom. as a result electrone repal. So, electrone are move to one to other atoms. So, atoms get one side positive and other side is negative, due to this we get attraction between positive and negative part of an atoms. this attraction is called LDF.

London dispersion forces examples

For example, – chlorine (Cl)

When two chlorine is close to each other and LDF are caused by emotion of electron in one molecules can induce a dipole in a atoms. electrone of one chlorine atom repel to other chlorine atom. so, electrone are starting moving one molecule to other molecule. as a result one atom has parial positive charge and other chlorine atom has negative charge. it attract each other. it mean, it attract between a positive to negative part of chlorine atom. as a result london dispersion forces is generated between two chlorine atom as shown in figure.

it is temporary attractive forces due to electron in two adjacent atoms displaced. As a result, atom get temporary dipoles. they attract each other through the london dispersion forces. and basically, LDF occur in non polar molecules.

therefore, we can say that the force of attraction between instant dipole and induced dipole is LDF.

Difference between covalent bonds and ionic bonds;

Significance of london dispersion Forces

London dispersion forces are present in both polar or non polar molecules.

For example,

Non polar molecules – ccl4, ch4

Mono atomic molecules – H2, cl2, F2, O2, l2

these are more significant between non polar and mono atomic molecules. because there is not other poles are present in non polar and mono atomic molecules.

therefore, LDF significance is present on both of them.

Factor effecting the strength of LDF

basic concepts – the factor effecting the strength of london dispersion forces is,

  1. Number of electrone in atom or molecules.
  2. Size of atom or molecules.
  3. Polarizibility

There are two basic factor effecting of LDF. So, what will be factor effecting on LDF.

1. Number of electrone in atom or molecules,

First you know that, greater the no of electron in atoms or molecules. it mean, stronger will be the london dispersion forces.

If no of electron is more in atoms or molecules then atom has stronger london dispersion forces.

Important note

Larger electron in atom or molecules – More chances of Polarizability – greater london dispersion forces”

For examples,

  1. Br2
  2. He

Br2 has larger no of electron (70 e) so, you can say that it has stronger LDF. But in case of He, it has less no of electron (2e). so, you can say that it has not stronger LDF.

2. Size of atom or molecules

Yes, it is true if size of atom is more then the no of electrone is also more.

for example, – iodine

Iodine has bigger size. So, iodine has more electrone. it mean iodine has stronger london dispersion forces.

Other words,

Greater the size of atom or molecules, it mean greater the electrone. electron depends upon size of atoms.

For example – Carbon

Carbon has more electrone, so you can say that carbon has stronger London dispersion forces.

Larger electrone – more chances of polarizability – greater London dispersion forces.

3. Polarizability

If atom has good polarizability, it mean atom has strongest London dispersion forces.

For example,

Iodine

Iodin exist solid form because it is strong London dispersion forces.

Weak necule hold on blance electrone.

It is easy to make pole.

but in case of fluorine electrone distribution are equal in orbital.


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