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 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, 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.
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.
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,
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.
this dipole is called induce dipole. and this intraction is called dipole induce dipole forces.
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.
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.
Significance of LDF
London dispersion forces are present in both polar or non polar molecules.
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,
- Number of electrone in atom or molecules.
- Size of atom or molecules.
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.
“Larger electron in atom or molecules – More chances of Polarizability – greater london dispersion forces”
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.
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.
If atom has good polarizability, it mean atom has strongest London dispersion forces.
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 flourine electrone distribution are equal in orbital.