Lattice Energy with explanation and calculation

       

To understand the concept of lattice energy , we should have knowledge about the formation of ionic crystal which is described as follows :-

In the formation of ionic crystals , a large number of cations and anions brought nearer to each other to form an ionic lattice and they arrange themselves in a regular pattern . This system gets stabilised on release of some energy and thus ionic crystal is formed . The amount of energy released in this process is called as Lattice Energy of the ionic lattice or solid .

Definition of Lattice Energy :- "The amount of energy released when one mole of the gaseous cations and one mole of the gaseous anions are brought closer to each other from an infinite distance to combine together to form one mole of ionic crystal , is known as Lattice Energy of that ionic solid"

As because the energy is released , it is denoted with a negative sign .

Alternate Definition of Lattice Energy:- "The amount of energy needed to break one mole of the ionic solid into its constituent gaseous ion is known as Lattice energy of that ionic solid ."

In this case , the lattice energy will be denoted by a positive sign .

Factors affecting Lattice Energy of ionic solids:-

1. Charge on cation or anion or product of charges : The extent of lattice energy will be greater if the charge on cation/anion or the product of charges is greater .

2. Size of cation or anion : Lattice energy is inversely proportional to the inter-ionic distance between the ions . But inter-ionic distance is sum of size of cation and anion . Therefore indirectly size of cation and (or) anion is inversely proportional to lattice energy , i.e. if the size of a cation or anion is smaller for the given anion or cation , the magnitude of the lattice energy will be greater .

Calculation of Lattice Energy :-

Lattice energy is equivalent to potential energy of ionic solid and it is calculated with the help of following equation :

                            PE = - (AZ₁Z₂e²)/r

where Z and Z are the charges on the ions , e is electronic charge , r is the distance between two ions and A is Madelung Constant (different for different crystal structure types) .

This was Lattice Energy . Hope it will be helpful to you and you liked it .

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