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Author Topic: Atomic Radii of Nitrogen, Oxygen and Fluorine  (Read 11910 times)

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xstrae

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Atomic Radii of Nitrogen, Oxygen and Fluorine
« on: July 28, 2006, 08:06:16 AM »

  N              O             F
70pm       74pm       72pm

Why is the radii of Oxygen higher than that of Nitrogen and why is Fluorine's atomic radius higher than that of nitrogen's? Shouldnt the atomic radii be decreasing along a period as the electrons are added to the same shell whereas as the number of protons increases. Theregore, the nucelar attraction becomes greater and the atomic radii should become smaller.. Isnt this correct?

My thoughts were in in this direction: Nitrogen has a more stable configuration as it's 2p orbital is half filled. So it must be closer to the nucleus. In the case of Oxygen, this stability is lost and the atomic radius increases due to greater electron-electron repulsion.
Is this right or am i totally lost? please help :(
« Last Edit: July 29, 2006, 01:10:46 AM by konichiwa2x »
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xiankai

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #1 on: July 28, 2006, 04:17:29 PM »

that sounds alright. after all there are 3 main factors atomic radii;

1) nuclear attraction
2) electron shielding effect
3) no. of quantum shells filled

and since (2) and (3) are relative constant for the elements you have mentioned, electron-electron repulsion in an orbital is a small factor that starts to count.
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Alberto_Kravina

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #2 on: July 29, 2006, 12:08:58 AM »

  N              O             Fl
70pm       74pm       72pm

Fl? Did you discover a new element?

;)
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xstrae

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #3 on: July 29, 2006, 01:11:44 AM »

thanks xiankai for clearing that.

Quote
Fl? Did you discover a new element?
my apologies. :P i must have been sleepy while typing that

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Mitch

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #4 on: July 29, 2006, 06:42:13 AM »

Flerovium? That's a joke no one is going to get. :P
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skyglow1

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #5 on: July 29, 2006, 07:43:49 PM »

Yes you are thinking correctly :)

I'm doing CIE AS level chemistry, and if you are too then you might want to be aware of this: in your answer for a question like this its not that the nitrogen's p orbitals are half filled giving it stability, but rather its the inter-electron repulsion between the paired electrons in Oxygen that causes its larger atomic radii. "Half filled orbitals" would not get you any marks in the exam.

You should clarify with your teacher what sort of reasons you should put down if you were to answer this question.
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Will

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #6 on: August 02, 2006, 09:41:34 AM »

  N              O             F
70pm       74pm       72pm

I'll sound like an idiot if I'm wrong, but I think this data is incorrect.

Shouldnt the atomic radii be decreasing along a period as the electrons are added to the same shell whereas as the number of protons increases. Theregore, the nucelar attraction becomes greater and the atomic radii should become smaller.. Isnt this correct?

Basically, yes.

From the data I've looked at the atomic radius decreases from N to F. Check out webelements or wikipedia if you don't have a data book.
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xstrae

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #7 on: August 03, 2006, 02:02:07 AM »

I had this confusing initially. Both wikipedia and webelements list different figures for the atomic radii. However my chemistry textbook and some other reference books i came across listed the above said data.
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Will

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Re: Atomic Radii of Nitrogen, Oxygen and Fluorine
« Reply #8 on: August 03, 2006, 03:51:53 PM »

From different sources these are the atomic radii (in pm) I have found:

N,     O,      F.
65     60     50
56     48     42
155   152   147
155   152   135
75     73     71
75     73     72
70     66     64
75     65     57

They all follow the decreasing trend. Most of the data is quite old (1960s I think) and probably not as accurate as modern values. I'll try and find a good, more recent source for atomic radii. I'm not saying this data is completely inaccurate; most of the variance is due to different classifications of atomic radii and different methods of calculation and measurement.
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