The net positive charge felt by an electron after accounting for shielding by other electrons.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
The effective nuclear charge, Z_eff, is the net positive charge felt by an electron after accounting for shielding by the other electrons. It is calculated as Z_eff = Z - S, where Z is the atomic number and S is the shielding constant. Z_eff rises across a period as protons are added without much extra shielding, and it changes only a little down a group. This explains trends in atomic radius, ionisation energy and electronegativity. A higher Z_eff pulls outer electrons closer to the nucleus.
Key ideas: Z_eff = Z - S, where S is the shielding constant, the net positive charge felt by an electron. For Na valence 3s, Z_eff is about 2.2 (Slater); across period 2 it rises about 0.65 per element. The attraction scales as Z_eff / r^2, which explains atomic size and ionization energy trends.
Common mistakes and connections: Students use the full nuclear charge Z for outer electrons or think Z_eff is constant down a group. In fact, it rises slowly down a group but n grows more. Same-shell electrons shield each other poorly (0.35 each). Z_eff ties to atomic radius, electronegativity, and ionization energy.
Zeff for the outer electron rises about 0.65 per element across period 2 because each extra proton is only weakly shielded by same-shell electrons. The interactive lesson shows this as a live animation or chart.
For a 2p electron of fluorine, Z = 9 and the shielding constant is about 3.8, so Z_eff is about 5.2.
The net positive charge felt by an electron after accounting for shielding by other electrons.
Effective Nuclear Charge is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Atomic Structure & Periodicity first: Exceptional Configurations of Cr and Cu, Valence Electrons, Core Electrons.
The next topics in Atomic Structure & Periodicity are Shielding Effect and Slater's Rules.
Yes. The interactive lesson includes a self-check question on Effective Nuclear Charge, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Effective Nuclear Charge is topic 70 of 115 in Atomic Structure & Periodicity.