What is ionization energy

What is the ionization energy? Definition and explanation ...

The Ionization energy, in literature too Enthalpy of ionization or Ionization energy called, indicates the energy that is required to remove an electron from an atom or molecule, which is in the gaseous state of aggregation.
Ionization describes in general the separation of an electron from an atom, e.g. by ionizing radiation. In the case of a neutrally charged atom, this means that it has a positive charge after the electron has been removed. Because electrons are negatively charged. The 'removal' of this negative charge leads to a positive excess charge in the atom.

Values ​​given in the periodic table generally relate to the first ionization energy. This relates to the energy required to remove the first, least strongly bound electron. Of course, more electrons, if any, can be removed from the atom. In this context one speaks of 'second ionization energy', 'third ionization energy', and so on. The energy required for this increases more and more with each electron that is to be removed further.

The force of attraction of the atomic nucleus essentially determines the energy required for ionization. The higher the attraction of the atomic nucleus on the electron, the more energy has to be expended. Helium is the chemical element with the highest ionization energy. This is particularly due to the electron configuration or the electron shell of helium. The valence shell, i.e. the outermost electron shell in the electron shell, is also the only electron shell in helium. This makes the atomic nucleus particularly attractive to the electron. In stark contrast to an element such as silver: with a total of five electron shells, the valence shell is significantly further away from the atomic nucleus, which means that the force of attraction on the valence electrons is less. However, it must also be taken into account that silver has a significantly higher atomic number. This means that the attraction of the atomic nucleus is significantly stronger than that of helium. Nevertheless, the lower attraction force on the electrons, caused by the valence shell further out, predominates. Two rules can now be derived from this:

1. The ionization energy sinks within a group of the periodic table because new electron shells are added (this reduces the attraction of the atomic nucleus to the more distant valence electrons).
2. The ionization energy increases within a period of the periodic table because the atomic number increases (and with it the attraction of the atomic nucleus).