Science, Tech, Math › Science Enthalpy of Atomization Definition (Chemistry) Share Flipboard Email Print Enthalpy of atomization is the energy released when molecules break into their atoms. JGI/Jamie Grill / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated August 06, 2018 Enthalpy of atomization is the amount of enthalpy change when a compound's bonds are broken and the component elements are reduced to individual atoms. Enthalpy of atomization is always a positive value and never a negative number.Enthalpy of atomization is denoted by the symbol ΔHa. How Enthalpy of Atomization Is Calculated If pressure is held constant, enthalpy change equals the change in the internal energy of a system. So, enthalpy of atomization equals the sum of the enthalpies of fusion and vaporization. For example, for the diatomic molecule chlorine gas (Cl2), the enthalpy of atomization under standard conditions is simply the bond energy of Cl2. All that is needed to atomize the substance is to break the bonds between gaseous molecules. For sodium (Na) metal at standard conditions, atomization requires separating atoms joined by metallic bonds. The enthalpy of atomization is the sum of the enthalpy of fusion and the enthalpy of vaporization of sodium. For any elemental solid, the enthalpy of atomization is the same as the enthalpy of sublimation. Related Term Standard enthalpy of atomization is the enthalpy change that occurs when one mole of a sample is dissociated into its atoms under standard conditions of 298.15 K temperature and 1 bar of pressure.