The ionisation potential (i.e. the first ionisation potential) is the energy required to remove the outermost electron from a neutral gaseous atom.
The second, and third ionisation potentials, etc. relate to the removal of the second, and third electrons respectively, and are higher than the first ionisation potential, as each successive electron is removed against increasing positive charge. The ionisation potential is usually expressed in electron volts and is determined from spectra.
Since it is possible to remove more than one electron from some atoms, an atom can have more than one ionization potential (IP).
M ==> M(+) + e(-) (I1 = First Ionisation Potential )
M+ ==> M(++) + e(-) (I2=Second Ionisation Potential )
M++ ==> M(+++) + e(-) (I3=Third Ionisation Potential)
The magnitude of the ionisation potential values depend on various factors, including
- the size of the atom,
- the charge on the nucleus,
- the screening effect of the inner electrons, and
- the type of the electron to be removed .
