Cation and anion attract each other by electrostatic force of attraction to give a molecule A⁺ B⁻. Since the electrostatic field of a charged particle extend in all directions, a positive ion is surrounded by a number of negatively charged ions while each negative ion similarly surrounded by a number of positive ions. These cations and anions arrange systematically in an alternating cation-anion pattern. This is called a crystal lattice. This process of clustering ions increases the force of attraction and thus potential energy decreases. The energy released when the requisite number of positive and negative ions are condensed into crystal to form one mole of the compound is called Lattice energy.
Higher the lattice energy, greater will be the ease of forming an ionic compound.
The value of lattice energy depends on the charges present on the two ions and the distance between them. According to coulomb's law, the force of attraction (F) between two oppositely charged ions in air with charges equal to q₁ and q₂ and separated by a distance d is given by,
F= (1/4πε₀K)*q₁q₂/d²
Where d is equal to sum of ionic radii of the two ions and K is dielectric constant of medium.
F=(1/4πε₀K)*q₁q₂/(rA⁺+rB⁻)²
The value of F increase if (i) q₁ and q₂ are high and (ii) (rA⁺+rB⁻) is small.
The stability of the ionic compound and the strength of the ionic bond depends on the value of F. Higher the value of F, greater shall be the stability of the ionic compound and hence greater shall be the strength of the ionic bond. For example, NaCl is more stable than CsCl as (rNa⁺+rCl⁻) is less than (rCs⁺+rCl⁻). MgO is more stable than NaCl as the product q₁q₂ is four times more in MgO than NaCl.
Higher the lattice energy, greater will be the ease of forming an ionic compound.
The value of lattice energy depends on the charges present on the two ions and the distance between them. According to coulomb's law, the force of attraction (F) between two oppositely charged ions in air with charges equal to q₁ and q₂ and separated by a distance d is given by,
F= (1/4πε₀K)*q₁q₂/d²
Where d is equal to sum of ionic radii of the two ions and K is dielectric constant of medium.
F=(1/4πε₀K)*q₁q₂/(rA⁺+rB⁻)²
The value of F increase if (i) q₁ and q₂ are high and (ii) (rA⁺+rB⁻) is small.
The stability of the ionic compound and the strength of the ionic bond depends on the value of F. Higher the value of F, greater shall be the stability of the ionic compound and hence greater shall be the strength of the ionic bond. For example, NaCl is more stable than CsCl as (rNa⁺+rCl⁻) is less than (rCs⁺+rCl⁻). MgO is more stable than NaCl as the product q₁q₂ is four times more in MgO than NaCl.
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