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Shielding effect stays constant across a period because number of inner electrons stays the same.

Well, that's not true.

It only works for the period =1,2,3 but in period 4, the number of inner electrons of $K$ to $Cu$ is 18,while the number of inner electrons from $Zn$ to $Kr$ is 28. So the number of inner electrons is not the same, so the shielding effect isn't constant.

Now there is another definition i saw at more than 3 sites which i found it more sensible and works well, is that :

The shielding effect stays constant across a period because number of inner shells stays constant.

And that is true because at period 4, number of inner shells is 3 for all elements in period 4, and this works for all periods.

So what is the right definition?

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  • $\begingroup$ Neither. Shielding effect is variable across all periods, as verious shielding is provided by inner electrons as well as be the peer electrons from the same orbital group. $\endgroup$
    – Poutnik
    Nov 2 '21 at 16:34
  • $\begingroup$ dude why the internet is like this loll. Every page i go there is a different answer, i've got to a point where i am so confused if what i learn is right or not smh $\endgroup$ Nov 2 '21 at 16:40
  • $\begingroup$ Do not look for answers, look for understanding to get your own answers. See Slater rules $\endgroup$
    – Poutnik
    Nov 2 '21 at 16:51
  • $\begingroup$ I've seen the Slater rules, but we didn't get that far in the course, so i don't think Slater rules will help in my case. About understanding point, i've understood shielding effect but i want to make sure which definition is correct to improve my understanding and help me in my exams, anw big thanks man! :) $\endgroup$ Nov 2 '21 at 17:03
  • $\begingroup$ It is not about definition, but about the scope of considered factors, which depends on the education level. $\endgroup$
    – Poutnik
    Nov 2 '21 at 17:33