London Dispersion Forces: Bond Types, Formula & Examples

London Dispersion Force is the weakest of all intermolecular forces. This force occurs between two different molecules that come close to each other. London dispersion force is also called a dipole-induced dipole attractive force wherein the atoms make temporary dipoles. 

Combination of atoms forms molecules bound together by chemical bonds. The article discusses the London dispersion force, and types of bonds between atoms and illustrates the dispersion force with the help of examples. 

Read More: Chemical Bonding & Molecular Structure

Keyterms: Force, Intermolecular force, molecules, dipole-induced dipole, atoms, chemical bond, dispersion force, dipoles, electrons

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London Dispersion Forces

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London dispersion forces were first discovered by the German Physicist Fritz London. London dispersion forces are found to occur between all molecules when two electrons in two different parts of an atom make instantaneous temporary dipoles. The then-produced force is known as London Dispersion Force. The force is also called dipole-induced dipole attraction force. Some of the characteristics of London Dispersion Forces are:

• London Dispersion Force is produced when two atoms are in close proximity to each other.
• They are the weakest types of intermolecular force which can lead the nonpolar matters to condense. 
• This property of London dispersion forces is employed in freezing liquids into the solids. 
• Freezing occurs when the temperature gradually lowers.
• The molecules are said to be polar when London Dispersion forces cause a dipole-induced dipole attraction between the atoms of the molecule.
• Some of the other intermolecular forces existing between molecules are ionic forces, dipole-dipole forces, and hydrogen bonds.

London Dispersion Force

Read More: Hydrogen Bonding

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London Dispersion Force Formula

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The formula for London Dispersion Force is given below. The ability of the molecules to produce separation of charge or the induced dipole is known as polarizability. Hence, when the two dipoles interact with each other, the main parameter involved in binding the molecules is strength. The strength is denoted by ’μ’. 

The strength of the dispersion force is directly proportional to the strength of the electric field. The electric field is denoted by E.

Therefore, 

\(\mu = \alpha \times E\)

where, μ = Induced Dipole Moment

\(\alpha\) = polarizability

E = Electric Field

The interaction energy can be calculated by using the London Dispersion Force formula.

Here, V11 is the potential energy between two molecules or atoms that are identical. This formula was later modified as follows for two un-identical atoms or molecules:

Here,

 I= Ionization Energy

A = polarizability

r= distance between the atoms

Read More: Potential Energy

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London Dispersion Forces Examples

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The electrons which are distributed unequally in the nucleus of the atom can produce dipole moments. When the other atoms or molecules get closer to the dipole it results in the formation of electrostatic attractive force between the atoms or molecules.

Let's understand this with an example. 

• The covalent bonds are formed by the equal distribution of valence electrons. 
• Both the atoms of Chlorine are bonded by a covalent bond. 
• The force between the two chlorine atoms is the London dispersion force. 
• This type of force of attraction is formed because of the unequal distribution of the electrons within the molecule. 

Temporary Dipoles in Two Non-Polar Diatomic Molecules

Read More: Diatomic Molecules

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Types of Bonds

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The different types of bonds existing between molecules can be classified as follows:

1. Ionic Bond
2. Covalent Bond
3. Coordination Bond

Let us understand each of these in a little detail.

Ionic Bond

These are formed by cations and anions by the mechanism of either losing or gaining electrons thereby giving the molecule a positive or negative charge. Some interesting characteristics of ionic bonds are listed below:

• When an atom accepts an electron, it forms an anion with a negative charge
• When an atom donated an electron, it forms a cation with a positive charge
• Ionic bond is formed by the electrostatic force of attraction between the cation and the anion
• A classic example of an ionic bond is NaCl which is formed by the ionic bond between the ions Na+ and Cl-.

Ionic Bond in NaCl

Read More: Polyatomic Ion

Covalent Bond

The octet formation gets completed during the process of sharing of electrons between two atoms. Covalent bonds are typically formed between two polar or non-polar non-metals. Some of the characteristics of covalent bonds are:

• The polarity of the covalent bonds is based on the electronegativities of the bonded atoms.
• Metals lose electrons to form metal cations.
• The free electrons in the lattice structure of the metal remain there.
• This electrostatic force of attraction between metal ions and the freely available mobile electrons forms a metallic bond. 
• This metallic bond is responsible for the specialized properties of metals like ductility, malleability, etc.

Read More: Physical Properties of Metals & Non-Metals

Coordination Bond

These bonds are formed by the unequal sharing of electrons between two atoms. Some of the interesting features are as follows:

• One of the atoms acts as an acceptor and the other acts as a donor. 
• Coordination bonds are formed between atoms that form molecules.
• The coordinate bond is denoted with an arrow ‘ →’ that points towards the acceptor to the donor of the atom.
• The atom forming the coordinate bond becomes stable once the electron pair is shared.
• The fundamental principle involved in coordinate bond formation is dependent on the Lewis Theory.

Read More: Coordination Number

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Things to Remember

• London dispersion force is the temporary attractive force that is produced due to the formation of temporary dipoles by atoms. 
• This is the weakest intermolecular force of atoms. 
• There are different types of Chemical bonds such as Covalent bonds, ionic bonds, metallic bonds, coordination bonds, etc. 
• There are different types of intermolecular forces: London dispersion force, dipole-induced force, ion-ion force, and hydrogen bonding. 
• These bonds are mainly formed by the sharing of electrons between atoms. 

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