## Atomic Sizes!!

I have the following assignment question:
Which member of the following pairs would you expect to be larger:
a) Li or F
b) Li or Li+
c) F or F-

a) At first I thought Li and F would be about the same size since they both have electrons in the first 2 orbitals. But then I read somewhere that sizes get smaller as you move along a period from left to right because the increased number of protons draws the electron orbitals tighter towards the centre, so F would be smaller than Li :?: And then someone told me that F would be bigger than Li because it has more electrons and a p orbital as well s orbitals.
So now I'm confused :? I'm inclined to go with the second option, F being smaller than Li...

b) I assume Li+ is smaller than Li since in losing an electron it also loses the only electron it had in the 2nd orbital plus the protons will draw the remaining 2 electrons tighter to the shell :?:

c) F and F- would be the same size:?: since the extra electron would fit into the same outer orbital (valence orbital :?:) as the electrons already there :?:

Any comments most appreciated...

thanks
joel

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You can view the atomic radii interactively at

for instance. This will tell you about the relative sizes of Li and F - and you cna then start rationalising what that plot shows

### Re: Atomic Sizes!!

a) [quote="joelus"]
But then I read somewhere that sizes get smaller as you move along a period from left to right because the increased number of protons draws the electron orbitals tighter towards the centre, so F would be smaller than Li[/quote]
That is correct.

b)Li has the larger radius because it has more electrons than Li+
c)F- has the larger radius because it has more electrons than F

The interactive periodic table does show it well.

WebElements: the periodic table on the WWW [http://www.webelements.com/]

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