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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: shekharbadam on February 08, 2009, 10:00:43 AM

Title: atomic radius
Post by: shekharbadam on February 08, 2009, 10:00:43 AM

hi, i have a question about atomic radius...please explain, clarify me about this..

why the atomic radius of silicon is so similar to that of germanium, yet the radii of silicon and carbon are quite different? carbon atomic radius is 77 r/pm , for silicon it is 118  r/pm and for germanium it is 122  r/pm .

Title: Re: atomic radius
Post by: FeLiXe on February 08, 2009, 03:25:08 PM

probably that the d electrons in Ge are no shielding the nuclear charge as well. and that contracts the valence electrons

Title: Re: atomic radius
Post by: shekharbadam on February 09, 2009, 03:14:00 AM

Quote from: FeLiXe on February 08, 2009, 03:25:08 PM

probably that the d electrons in Ge are no shielding the nuclear charge as well. and that contracts the valence electrons

     


can u explain clearly?

Title: Re: atomic radius
Post by: FeLiXe on February 09, 2009, 12:55:07 PM

atomic radii are basically determined by two things:
- more electrons need more space (i.e. valence electrons have a higher principle quantum number)
- increasing nuclear charge contracts the atoms

over a big part of the periodic table those effects kind of cancel out and that is why atomic radii are rather similar for the different elements

the decisive factor how much nuclear charge is actually "seen" by a valence electron and how much is shielded by the inner electrons. d and especially f electrons are not as good at shielding the nucleus, that is why the valence electron experiences more charge and the atom is contracted. that is kind of the idea behind it. you could for example calculate the nuclear charge of the outer electrons according to Slater's rules (http://en.wikipedia.org/wiki/Slater%27s_rules) and you should see that Ge has a higher effective charge (if I am not wrong)