Zeffo

Zeffo, or effective nuclear charge, is the net positive charge experienced by an electron in an atom. While the nucleus (center) has a full positive charge from protons, electrons in the inner shells partially shield outer electrons from this pull. Zeff accounts for this shielding, revealing how strongly an outer electron is attracted to the nucleus. A higher Zeff means the electron feels a stronger pull, making it more tightly bound and less likely to be removed. It helps explain why electrons closer to the nucleus are held more tightly than those farther away.