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Author Topic: Why is helium smaller than hydrogen ?  (Read 25043 times)

Offline ChinaCat

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Why is helium smaller than hydrogen ?
« on: 05/01/2004 16:00:46 »
:D Hi guys- I just stumbled onto this site and am hoping that someone can help answer this question:

Why is a helium atom smaller than a hydrogen atom?

I know that mass-wise, the H atom is smaller. Is the question referring to the amount of space that the He atom takes up???

Please help if you know-- this question was in a review guide for an exam I am taking this weekend and it's driving me nuts. I can't find a good explanation anywhere!







« Last Edit: 31/05/2004 05:36:31 by NakedScientist »


 

Offline Ylide

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Re: Why is helium smaller than hydrogen ?
« Reply #1 on: 06/01/2004 02:32:33 »
Along a period (left to right) the the atomic number increases while the valence electrons remain in the same shell. Thus due to the increasing nuclear charge (pulling electrons closer to the nucleus) the radii of the atoms decrease left to right.

And as you can see from the table, Hydrogen and Helium are in the same period.

Hope that helped.



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Offline Supercryptid

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Re: Why is helium smaller than hydrogen ?
« Reply #2 on: 07/01/2004 01:41:25 »
Yes, cannabinoid summed that up correctly.

Data about the generallized radius of the helium atom is difficult to come by since helium does not bond with other atoms. If any measurement is given, it is usually either theoretical or is a measure of the "van der walls" radius, which is much different than the covalent radius used for many other atom's measures.
 

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Re: Why is helium smaller than hydrogen ?
« Reply #2 on: 07/01/2004 01:41:25 »

 

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