ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

Effective nuclear charge refers to the net positive charge that an electron experiences from the nucleus of an atom, taking into account the shielding effect caused by other electrons. This concept is crucial in understanding various atomic properties, such as atomic size, ionization energy, and electron affinity.

In an atom, the positively charged protons in the nucleus attract negatively charged electrons. However, inner electrons partially shield outer electrons from this nuclear charge. This results in outer electrons experiencing a reduced charge, referred to as the effective nuclear charge. The effective nuclear charge can be approximated by the formula \( Z_{\text{eff}} = Z - S \), where \( Z \) is the total number of protons (the atomic number), and \( S \) is the shielding constant, representing the extent to which other electrons shield the outer electron from the full nuclear charge.

Understanding effective nuclear charge helps explain why elements display periodic trends in properties, as it affects how tightly electrons are held by the nucleus and their overall interactions within the atom.