[sasha44 (OP)]

What about the comparison of van der Waals radius and covalent radius of these two the same or different?
And if there is a difference why is that?

okay
http://www.pci.tu-bs.de/agbauerecker/VorlesungPCGrundlagenWasserstoffwirtschaft2011/MaterialZurVorlesung/UllmannsWasserstoff2011.pdf [nofollow]
This suggests the atomic radius and covalent atomic radius of Hydrogen differs from those of Deuterium
Ar of H is 1.007825 while Ar of D is of 2.0140
Mr of H2 is 2.016 while Mr of D2 is 4.029

But still it doesn't say why 

[Bored chemist]

The answer is complicated.
It involves this
http://en.wikipedia.org/wiki/Zero-point_energy

[damocles]

There is a difference but:
(1) the figures you quote are molar mass figures, not atomic radius.
(2) D and D2 are smaller than H and H2 respectively, and the difference is quite small.

The difference is less than 1%, and it is not quoted because there are several different ways of estimating the size of an atom or molecule, and the difference between the two isotopes of hydrogen is less than the uncertainty in any of the estimates. We know that D2 is smaller than H2 because of the sorts of considerations outlined in the article referenced by BC above.

[sasha44 (OP)]

Thanks!
I figured it out during the tute class. Apparently we don't have to think that much, just assume the radii are equal when it is not given and different when the two values are given.

The answer is complicated.
It involves this
http://en.wikipedia.org/wiki/Zero-point_energy [nofollow]

I read that  I am guessing you mean the gravitational forces due to the extra mass in D ?

[Bored chemist]

It's not a gravitational effect as such, it's a quantum mechanical one.