How can I know that?
I only know that while we going to the right side at the table so the radius is decreasing.
And while we going down, so the radius is bigger.

But how can I check that radiuses in this case ?


Think of it this way:

1) Count the electrons (all of them) in each atom or ion.

2) What happens to the orbitals, and thus to atoms or ions with a given number of electrons (let us say, 18 electrons), when you increase the atomic number of the element (more protons in the nucleus)?

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