CBSENEETJEEClass 11

What is ionization enthalpy?

Answer

Ionization enthalpy is the minimum energy required to remove the most loosely bound electron from an isolated gaseous atom in its ground state.

The working

Definition

It is the energy needed to knock out the outermost electron from one mole of gaseous atoms to form gaseous cations.

Representation

For an atom X, the process is X(g) → X⁺(g) + e⁻, and the energy absorbed is the ionization enthalpy.

Periodic trend

It generally increases across a period and decreases down a group as atomic size grows.

Key point

It is always positive because energy must be supplied to overcome the attraction of the nucleus for the electron.

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