Ionization energy is defined as the energy required by an atom to remove the electron from the valence shell.
Ionization energy is an endothermic process as the energy is absorbed by the electron to come out and is generally represented as I.P.
Ionization potential or Ionization energy can be calculated in electron volts.
The energy required to remove the first electron is called the first ionization energy, and to remove the second electron it is called the second ionization energy.
Successive ionization energy is defined as the energy that is required to remove the electron one after the other.
Successive ionization energy will depend upon the number of electrons present in the outermost shell.