Atomic radii

[Melody Haratian 2J]

Hi everyone!
The atomic radii increases down a group and decreases across a period. I was wondering, which one has a greater effect on the atomic radii? Does going down a group increase the atomic radii more than going across a period would decrease the atomic radii?
Thanks!

[Jayasree Peri 2J]

Going down a group would increase the atomic radii more because you're adding a whole new energy level (a new shell). Going across a period decreases the atomic radii because of the attractions between the electrons in the valence shell and the protons in the nucleus; although it does decrease the atomic radii, it doesn't get rid of a whole shell in the way that going down a group adds a whole shell. Hope this helps!

[Jaden Joodi 3J]

^^^^^
The reason why the effect going across a row has such a lower effect on the decrease of the atomic radii is because of the electron shielding's limited effect. Increasing radii through gaining new shells is much greater of an effect.