Please Explain me the meaning of Points d) and e). :

Slater's rule to know screening constant ($\sigma$):
(d) Screening effect of (n-1) penultimate orbit s, p,d electrons is 0.85
(e) Screening effect of (n-2) and below all of e^- present in s, p, d, f is 1.0 From top to bottom in a group Z_eff remain constant 

Group	Element	Li	Na	K	Rb	Cs
	Zeff	1.30	2.20	2.20	2.20	2.20

 

 

Sceening effect value (Slater value) can be calculated for any element with their electronic configuration. 
For ex., 
Na¹¹ - 1s²2s²2p⁶3s¹

The screening effect of 3s electron is to be calculated. 
The 2s²2p⁶ electrons are all penultimate shell and penultimate shell (n-1) contribute 0.85. 
So its contribution is 8 x 0.85 = 6.8
1s² electrons are all (n-2)  orbit electrons and its contribution is 2x1 =2
Thus the total screening effect (Slater) value = 6.8+2=8.8
Z_eff = Z-S = 11 -8.8 = 2.2
Similarly we can calculate for all elements Z_eff value.