What is the Difference Between First and Second Ionization Energy (I1E vs I2E)?

The first and second ionization energies represent the energy required to remove electrons from an atom. The differences between these two energies are as follows:

• First Ionization Energy (I1E): This is the energy needed to remove the outermost, or highest energy, electron from a neutral atom in the gas phase. As the atomic radius decreases, it becomes harder to remove the electron that is closer to a more positively charged nucleus. Ionization energy generally increases from left to right in a period and decreases from top to bottom in a group.
• Second Ionization Energy (I2E): This is the energy required to remove an electron from a 1+ ion (meaning the atom has already lost one electron and now removing the second). The second ionization energy is always higher than the first ionization energy because it requires even more energy to remove an electron from a cation than it is from a neutral atom.

The third ionization energy represents the energy required to remove a third electron, and so forth. In general, ionization energy increases with each subsequent electron removal. The ionization energy of a chemical species is different for electrons of different atomic or molecular orbitals.

Comparative Table: First vs Second Ionization Energy (I1E vs I2E)

The first ionization energy (I1E) is the energy required to remove the least bound (outermost) electron from a neutral atom, while the second ionization energy (I2E) is the energy required to remove the outermost electron from a positively charged ion (1+ ion) of the element. Here is a table comparing the first and second ionization energies for some selected elements:

The second ionization energy is always larger than the first ionization energy because there is a stronger nuclear charge once an electron is removed from the atom. This makes it more difficult to remove the second electron compared to the first one.