What is ionization energy measured in?
The unit that ionization energy is measured in depends on whether you are a physicist or chemist.
Ionization energy is defined as the minimum amount of energy needed to remove an electron from an atom or molecule in it's gaseous state.
In physics, the ionization energy is measured in electron volts (eV) and measures how much energy is needed to remove one electron from one atom or molecule.
In chemistry, the ionization energy is measured per mole of atoms or molecules and is expressed in kiloJoules per mole (kJ/mol). It measures how much energy or enthalpy is needed to remove an electron from all of the atoms or molecules in one mole.