Effective nuclear charge, Zeff

Definition

Effective nuclear charge, $Z_{eff}$, is the net positive charge experienced by an electron in a multi-electron atom. It accounts for both the actual nuclear charge and the shielding caused by other electrons.

5 Must Know Facts For Your Next Test

1. It increases across a period due to increasing proton number with minimal addition of shielding electrons.
2. It affects atomic size; atoms with higher $Z_{eff}$ tend to be smaller because the electrons are pulled closer to the nucleus.
3. The formula for calculating effective nuclear charge is $Z_{eff} = Z - S$, where $Z$ is the atomic number and $S$ is the shielding constant.
4. Electrons in inner shells shield outer-shell electrons more effectively than those in the same shell.
5. In multi-electron atoms, core electrons contribute more significantly to shielding than valence electrons.

Review Questions

• What is the trend of effective nuclear charge across a period?
• How does effective nuclear charge influence atomic radius?
• What does $S$ represent in the formula $Z_{eff} = Z - S$?

Related terms

Atomic Radius: The distance from the nucleus of an atom to its outermost electron shell.

Shielding Effect: The reduction in effective nuclear charge on an electron cloud due to repulsion from other electrons within an atom.

Ionization Energy: The energy required to remove an electron from a gaseous atom or ion.