Enthalpy of atomisation: the definition and the diatomic trap
Dr Lavan Ganeshkumar, PhD · updated 4 October 2026
The enthalpy of atomisation is the enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
Words that must appear
- One mole of gaseous atoms
- From the element in its standard state
The sign
Always endothermic, so positive. Energy is taken in to separate particles or break bonds.
Do not confuse with
Bond enthalpy, which counts bonds broken. Atomisation counts one mole of atoms formed.
Common questions
What is the enthalpy of atomisation?
The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
Is the enthalpy of atomisation positive or negative?
Positive. It is always endothermic.
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