The effective nuclear charge (Zeff) represents the net positive charge experienced by an individual electron in a multi-electron atom. It is less than the actual nuclear charge (Z), due to the shielding or screening effect of other electrons in the atom. To determine this value for a valence electron within a specific element, one must account for the extent to which the inner, core electrons reduce the attractive force exerted by the nucleus.
Understanding the effective nuclear charge is crucial for rationalizing various atomic properties, such as ionization energy, atomic size, and electronegativity. A higher effective nuclear charge implies a stronger attraction between the nucleus and the valence electrons, leading to increased ionization energy and smaller atomic radii. Historically, the concept emerged as a refinement of the simple Bohr model to better explain the behavior of electrons in more complex atomic systems.
