Lattice Energy

Introduction

The ionic stability of a solid is related to the lattice energy which is a form of potential energy. It takes a large amount of energy to break the bond between ionic solids as they are extremely stable. The effects of this can be seen when we consider the melting point. Sugar melts easily and we have seen many recipes that require sugar. Although salt which has a similar look does not melt at the temperature food cooks. This is because of the fact that salt or sodium chloride is an ionic solid that has very strong bonds. So, due to these strong bonds melting salt is difficult.

lattice_energy

The ionic solids have their ions arranged in a crystal lattice (as shown in the image). And because of this arrangement, they get their strength.

Lattice energy is also called as lattice enthalpy. An ionic solid is formed when gaseous ions combine together and release energy. In the same way, a certain amount of energy will be required to change the ionic solid into the gaseous ions (which it was made up of). The ions are held together by this energy and thus lattice energy is a measure of it.

Lattice dissociation enthalpy is the energy required to break the ionic bonds of the solid state and form the gaseous ion. Lattice formation enthalpy is the energy that is released when the gaseous ionic components bind together to create ionic solid.

The energy state of an ionic solid is lower than the gaseous ions and thus they are more stable. from here we get the conclusion that lattice dissociation enthalpy will always be positive and lattice formation enthalpy will be negative. The lattice energy will be larger with a stable ionic solid and bonds that are more stable are harder to break. Just like a chair that has been nailed together is better protected against breakage than a chair stuck together with gum.

Factors that Influence Lattice Energy

There are two factors that affect the lattice energy.

Ionic Charge – Lattice energy is greater in ions that have greater charge.

Ionic Radius – As we know by now, the ionic radius is the measurement of the size of the ion. Lattice energy is higher in compounds that have smaller ions because the ions are packed closer together.


Practise This Question

Chromatography is used to separate