Effective nuclear charge

In atomic physics, the effective nuclear charge of an electron in a multi-electron atom or ion is the number of elementary charges (${\displaystyle e}$) an electron experiences by the nucleus. It is denoted by Z_eff. The term "effective" is used because the shielding effect of negatively charged electrons prevent higher energy electrons from experiencing the full nuclear charge of the nucleus due to the repelling effect of inner layer. The effective nuclear charge experienced by an electron is also called the core charge. It is possible to determine the strength of the nuclear charge by the oxidation number of the atom. Most of the physical and chemical properties of the elements can be explained on the basis of electronic configuration. Consider the behavior of ionization energies in the periodic table. It is known that the magnitude of ionization potential depends upon the following factors:

1. The size of atom
2. The nuclear charge; oxidation number
3. The screening effect of the inner shells
4. The extent to which the outermost electron penetrates into the charge cloud set up by the inner lying electron

In the periodic table, effective nuclear charge decreases down a group and increases left to right across a period.