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Topic: Atomic Radii  (Read 5680 times)

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Offline Procrastinate

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Atomic Radii
« on: June 06, 2011, 08:04:40 AM »
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.

Offline DevaDevil

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Re: Atomic Radii
« Reply #1 on: June 06, 2011, 10:29:20 AM »
Rb is larger than I.... in atomic radius, it is smaller only in ionic radius

Offline vmelkon

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Re: Atomic Radii
« Reply #2 on: June 08, 2011, 05:40:07 PM »
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.

Offline Kalesin

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Re: Atomic Radii
« Reply #3 on: June 10, 2011, 04:04:00 PM »
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!  8)
Chemistry is a party of electrons!

Offline Borek

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Re: Atomic Radii
« Reply #4 on: June 10, 2011, 04:32:11 PM »
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.
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Offline Kalesin

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Re: Atomic Radii
« Reply #5 on: June 10, 2011, 05:16:19 PM »
I'm pretty sure I'm not missing anything, but sure, lets make an easy question hard  ;D  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.
Chemistry is a party of electrons!

Offline Borek

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Re: Atomic Radii
« Reply #6 on: June 10, 2011, 05:46:06 PM »
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.
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Offline Kalesin

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Re: Atomic Radii
« Reply #7 on: June 10, 2011, 05:56:35 PM »
Well yeah, maybe I misinterpreted, that the radius increases in groups because of mroe electrons, it's actually because of more protons  ;D Thanks for correcting me!
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Offline BluePill

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Re: Atomic Radii
« Reply #8 on: June 11, 2011, 12:41:33 AM »
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.

Offline vmelkon

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Re: Atomic Radii
« Reply #9 on: June 11, 2011, 09:15:41 AM »
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.

Offline Kalesin

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Re: Atomic Radii
« Reply #10 on: June 11, 2011, 06:19:07 PM »
Oh sorry, I meant to say decreases* in my last post  ;D Sorry for making you confused  :'(
Chemistry is a party of electrons!

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