IB Chemistry - Energetics

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Ionic compounds are giant structures in which the simplest particles are ions. These ions are held together by strong electrostatic forces. The same laws of thermodynamics apply to ionic compounds as to covalent compounds. In this chapter we look at the application of the law of conservation of energy and Hess' law to ionic systems

Syllabus reference

Reactivity 1.2.5 - A Born–Haber cycle is an application of Hess’s law, used to show energy changes in the formation of an ionic compound. (HL)

  • Interpret and determine values from a Born–Haber cycle for compounds composed of univalent and divalent ions.


  • The cycle includes: ionization energies, enthalpy of atomization (using sublimation and/or bond enthalpies), electron affinities, lattice enthalpy, enthalpy of formation.
  • The construction of a complete Born–Haber cycle will not be assessed.

Tools and links

  • Structure 2.1 - What are the factors that influence the strength of lattice enthalpy in an ionic compound?

In Chapter 4.5