Explaining weird trend of d- and f- block elements.

[ash64449]

Hello friends,

I noticed from Wikipedia the following information:
Atomic radii:
4th period(only d-block elements):
Sc:160 pm
Ti : 140 pm
V : 135 pm
Cr : 140 pm
Mn: 140 pm
Fe : 140 pm
Co : 135 pm
Ni : 135 pm
Cu :135 pm
Zn : 135 pm

Normally across the period atomic radii should decrease. But d-block elements do not follow this trend. It increases From V to Cr and them remains constant and decreases and remains constant again.

So they show horizontal similarities too.. Can some one explain me this strange trend?

More stranger trend is of f-block elements.. They don't change their radii at all if we go across the period!

 

[DrDu]

As far as I remember the experimental radii are half the distance of the atoms in a crystal lattice.
However, the metals crystalize in different lattices, which influences the radii.
Better take the calculated values from the table below.

 

[ash64449]

As far as I remember the experimental radii are half the distance of the atoms in a crystal lattice.
However, the metals crystalize in different lattices, which influences the radii.
Better take the calculated values from the table below.

Which table? can you explain this trend?

Not only this one,ionization enthalpy too follow the same way as atomic radii. But a little difference.

So i thought understanding atomic radii would help to understand everything.

 

[DrDu]

Which table?

I meant the table with the theoretical atomic radii by Clementi in
http://en.wikipedia.org/wiki/Atomic_radii

 

[ash64449]

I meant the table with the theoretical atomic radii by Clementi in
http://en.wikipedia.org/wiki/Atomic_radii

Why?

I mean that is theoretical. Shouldn't we go for experimental results?

Yes. the theoretical models follow the general trend. But i think we should stick to experimental results..

Do you think no satisfactory explanations can be given to the trend observed experimentally?

 

[ash64449]

Here is the exact link through which i referred: http://en.wikipedia.org/wiki/List_of_elements_by_atomic_properties

 

[DrDu]

The experimental values are derived from bond lengths of covalent substances. Hence you have to discuss the average bond lengths of d-block elements in mainly covalent compounds. This is much more complicated than discussing the shrinking of d- or f-orbitals.

 

[ash64449]

The experimental values are derived from bond lengths of covalent substances. Hence you have to discuss the average bond lengths of d-block elements in mainly covalent compounds. This is much more complicated than discussing the shrinking of d- or f-orbitals.

So, Can We say that d-block elements follow the same periodicity of that of s- and p- blocks?

I mean by experimental results obtained by deriving bond lengths, it is observed that some elements have same atomic radii.. i.e,they show horizontal similarities. s- and p- block don't show like that.

but theoretical models show no horizontal similarities.

 

[sveegaard]

My best guess is Slater-screening. Electrons can screen other electrons from the positively charged nucleus, but it depends on how the electrons occupy the orbitals (which itself seems random for d- and f-block elements). This way, depending on the screening of other electrons, the distance of the outer electrons from the nucleus can be very similar.

 

[ash64449]

My best guess is Slater-screening. Electrons can screen other electrons from the positively charged nucleus, but it depends on how the electrons occupy the orbitals (which itself seems random for d- and f-block elements). This way, depending on the screening of other electrons, the distance of the outer electrons from the nucleus can be very similar.

How is Slater-screening different from Shielding Effect?