# Chapter 7 - Periodic Properties of the Elements - Exercises: 7.32c

The value of the screening constant is estimated to be $S=11.25$

#### Work Step by Step

*Slater's rules state that - Electrons for which $n$ is larger than $n$ of the electrons of interest contribute 0 to $S$. - Electrons with the same value of $n$ as the electrons of interest contribute 0.35 to $S$. - Electrons with value $n-1$ contribute 0.85 to $S$. - Electrons with even smaller values of $n$ contribute 1.00 to $S$. Both $Cl^-$ and $K^+$ have the same electron configuration $1s^22s^22p^63s^23p^6$. That means with an electron with $n=3$, - 2 electrons in $n=1$ each contributes 1.00 to $S$. - 8 electrons in $n=2$ each contributes 0.85 to $S$. - 8 electrons in $n=3$, but only 7 each contributes 0.35 to $S$ (excluding 1 electron of interest). Therefore, the value of the screening constant is $$S=2\times1.00+8\times0.85+7\times0.35=11.25$$

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