#### Answer

The effective nuclear charge of Si is $4.15+$ and that of Cl is $6.1+$.

#### Work Step by Step

1) $Si$:
The nuclear charge of $Si$ is $Z=14+$.
The outermost electrons of Si is in the $n=3$ shell.
Si has:
- 2 electrons in the $n=1$ shell, each of which contributes 1.00 to $S$.
- 8 electrons in the $n=2$ shell, each of which contributes 0.85 to $S$.
- 4 valence electrons in the $n=3$ shell, but only 3 of which each contributes 0.35 to $S$ (minus the screening effect of 1 electron to itself).
That means $S=2\times1+8\times0.85+3\times0.35=9.85$
Therefore, $$Z_{eff}=Z-S=(14+)-9.85=4.15+$$
2) $Cl$:
The nuclear charge of $Cl$ is $Z=17+$.
The outermost electrons of Cl is in the $n=3$ shell.
Cl has:
- 2 electrons in the $n=1$ shell, each of which contributes 1.00 to $S$.
- 8 electrons in the $n=2$ shell, each of which contributes 0.85 to $S$.
- 7 valence electrons in the $n=3$ shell, but only 6 of which each contributes 0.35 to $S$ (minus the screening effect of 1 electron to itself).
That means $S=2\times1+8\times0.85+6\times0.35=10.9$
Therefore, $$Z_{eff}=Z-S=(17+)-10.9=6.1+$$