The atomic radius of As is not so large than that of P Why?.?

Question

The atomic radius of As is not so large than that of P Why?.?

Answer 1

Because Arsenic (As) has more protons (more +) it holds its electrons (-) closer to its nucleus.

While you would expect it to have a larger radius with more electrons, realise that the extra electrons are NOT in the same configuration as p because they are in the new d orbital as opposed to the s or p orbital.

In other atoms this situation also happens, but there are often enough p or s electrons to shield the outer electrons from the proton effect.

Answer 2

The atomic radius  of As should be much larger than that of P due to higher value of n . But. due to d-block contraction effect the atomic size of As is not so large as expected.