## Chemistry: The Central Science (13th Edition)

The effective nuclear charge for the 2p electrons: $Z_{eff}(F^-)=7+$ and $Z_{eff}(Na^+)=9+$
The formula to calculate $Z_{eff}$ for the 2p electrons is $$Z_{eff}=Z-S$$ Z: the nuclear charge of the element S: the screening constant Both $F^-$ and $Na^+$ have 10 electrons and the same electron configuration: $1s^22s^22p^6$. That means for the 2p electrons, both have 2 core electrons and 8 valence electrons. Therefore, the screening constant $S$ of both $F^-$ and $Na^+$ for the 2p electrons is $$S=2\times1.00+8\times0.00=2.00$$ The nuclear charge of $F^-$ is $Z=9+$ The nuclear charge of $Na^+$ is $Z=11+$ Therefore, the effective nuclear charge of $F^-$ and $Na^+$ is $Z_{eff}(F^-)=(9+)-2.00=7+$ $Z_{eff}(Na^+)=(11+)-2.00=9+$