What is meant by the term effective nuclear charge, Z_eff, and what causes it?

Verified step by step guidance

1. The effective nuclear charge, denoted as \( Z_{\text{eff}} \), is the net positive charge experienced by an electron in a multi-electron atom.
2. It accounts for the actual nuclear charge (the total positive charge of the nucleus) and the shielding effect caused by other electrons in the atom.
3. The shielding effect occurs because inner electrons partially block the attraction between the nucleus and the outer electrons, reducing the full nuclear charge experienced by the outer electrons.
4. The effective nuclear charge can be estimated using the formula: \( Z_{\text{eff}} = Z - S \), where \( Z \) is the atomic number (total number of protons) and \( S \) is the shielding constant, representing the extent of electron shielding.
5. Understanding \( Z_{\text{eff}} \) is crucial for explaining trends in the periodic table, such as atomic size, ionization energy, and electron affinity, as it influences how strongly electrons are held by the nucleus.