Per wiki: Nuclear charge is the electric charge of a nucleus of an atom, equal to the number of protons in the nucleus times the elementary charge. In contrast, the effective nuclear charge is the attractive positive charge of nuclear protons acting on valence electrons, which is always less than the total number of protons present in a nucleus due to the shielding effect.[3]
The shielding effect sometimes referred to as atomic shielding or electron shielding describes the attraction between an electron and the nucleus in any atom with more than one electron. The shielding effect can be defined as a reduction in the effective nuclear charge on the electron cloud, due to a difference in the attraction forces on the electrons in the atom.
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Hillbillychemist
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Every electron in an atom is attracted to every proton in the atom and repelled by every other electron in that atom. Use of the term "shielding" is then somewhat misleading since a shield implies a barrier. In reality what is seen is a balancing of forces of attraction by the forces of repulsion. These forces are vector forces so core electrons (those inner electrons between the valence electrons and the protons in the nucleus) are more effective in balancing than are other valence electrons. The approximation is then to subtract the number of core electrons from the number of protons to determine the effective nuclear charge.