Trends in $Z_{\text{eff}}$​

Across a Period (Left to Right):

• Increases: Protons are added to the nucleus (Z increases), while shielding remains relatively constant.

• Result: Electrons are pulled closer to the nucleus, decreasing atomic radius.

Down a Group:

• Relatively Constant: Although Z increases, the number of inner electron shells increases significantly, increasing S, so the net Zeff​ felt by valence electrons changes little.

Applications of $Z_{\text{eff}}$​

1. Atomic Radius: Higher Zeff​ pulls electrons closer, reducing atomic size across a period.

2. Ionization Energy: Higher Zeff​ makes it harder to remove an electron, increasing ionization energy.

3. Electronegativity: Elements with high Zeff​ attract bonding electrons more strongly.

4. Electron Affinity: Higher Zeff​ results in a more negative electron affinity, as atoms more readily accept electrons.