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Which of the following are the causes of Lanthanide contraction?

(1) The decrease in ionic radii of the lanthanides from 103 pm (La$^{3+}$) to 86 pm (Lu$^{3+}$) in the lanthanide series.

(2) The poor shielding of nuclear charge (nuclear attractive force on electrons) by 4f electrons

(3) The poor shielding of nuclear charge (nuclear attractive force on electrons) by 5d electrons

(4) The same effective nuclear charge from Ce to Lu

$\begin {array} {1 1} Both (2) and (3) \\ Only (2) \\ Both (1) and (2) \\ (1), (2) and (4) \end {array}$

Can you answer this question?
 
 

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Answer: Only (2)
The effect results from poor shielding of nuclear charge (nuclear attractive force on electrons) by 4f electrons; the 6s electrons are drawn towards the nucleus, thus resulting in a smaller atomic radius.
(Therefore (1) is an effect not a cause).
answered Jan 30, 2014 by sreemathi.v
edited Aug 6, 2014 by balaji.thirumalai
 

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