[Procrastinate]

There is this question on my practice quiz that says: Which element has the largest atomic radius?

a.) Li b.) Na c.) Rb d.) F e.) I

I selected Rubidium because 1. It was one of the lowest period and 2. It was the first group and the common trend is that as you progress further across a period, the atomic radius will decrease.

However, it said Iodine was the answer and I am quite stumped.

[DevaDevil]

Rb is larger than I.... in atomic radius, it is smaller only in ionic radius

[vmelkon]

Rb is 248 pm
I is 140 pm

"However, it said Iodine was the answer and I am quite stumped. "

You do want the largest right? It is Rb.

[Kalesin]

Hello, I'm new here, but I think I can help you  If you have a periodic table in front of you, the radius of the atom increases in periods downwards, because there are more electron shells, but it decreases in groups from left to right, because atoms have more electrons, hence they are pulled towards the atomic nucleus, decreasing the atomic radius.

So to answer your question, Rb has the biggest atomic radius, because it has as much or more electron shells as all the other mentioned and the very least electrons.

Hope that helps! 

[Borek]

it decreases in groups from left to right, because atoms have more electrons, hence they are pulled towards the atomic nucleus, decreasing the atomic radius.

Actually the more electrons, the higher the radius. You are missing something important.

[Kalesin]

I'm pretty sure I'm not missing anything, but sure, lets make an easy question hard    As the atomic number increases along each row of the periodic table, the additional electrons go into the same outermost shell whose radius gradually contracts, due to the increasing nuclear charge.

[Borek]

It is not about making things hard, it is about making things correct and not confusing.

As the atomic number increases along each row of the periodic table, the additional electrons go into the same outermost shell whose radius gradually contracts, due to the increasing nuclear charge.

the radius of the atom (...) decreases in groups from left to right, because atoms have more electrons, hence they are pulled towards the atomic nucleus, decreasing the atomic radius.

Compare these two. One is correct, one is not.

[Kalesin]

Well yeah, maybe I misinterpreted, that the radius increases in groups because of mroe electrons, it's actually because of more protons  Thanks for correcting me!

[BluePill]

that the radius increases in groups because of mroe electrons, it's actually because of more protons

Is it me or I just got more confused?
If you have more protons, your radius would shrink because of increased effective nuclear charge.
Across a period, atomic radius decreases because of increased effective nuclear charge.
From top-to-bottom, atomic radius increases because of increased electrons and Slater shielding.

[vmelkon]

It is not as simple as "because of more protons".

Not every electron is attracted by the same amount of force by the nucleus.
It is well explained on some web pages so I'm not going to attempt to explain it here.

[Kalesin]

Oh sorry, I meant to say decreases* in my last post  Sorry for making you confused