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

Both Na and K are expected to experience the effective nuclear charge $Z_{eff}=+1$
1) $Na$: The nuclear charge of Na is $Z=+11$. There are 10 core electrons and 1 valence electrons. Each core electron contributes 1.00 and each valence electron contributes 0.00 to the screening constant. Therefore, $S=10\times1.00+1\times0.00=10$ Therefore, the effective nuclear charge of Na is $$Z_{eff}=Z-S=+11-10=+1$$ 2) $K$: The nuclear charge of K is $Z=+19$. There are 18 core electrons and 1 valence electrons. Each core electron contributes 1.00 and each valence electron contributes 0.00 to the screening constant. Therefore, $S=18\times1.00+1\times0.00=18$ Therefore, the effective nuclear charge of K is $$Z_{eff}=Z-S=+19-18=+1$$