What is the cause of Lanthanoid Contraction? Also what do u undertand by the term"shieldinf of 4f electrons"?

Asked by mohitgehlot | 3rd Mar, 2011, 01:00: AM

Expert Answer:

Dear Student

 The atomic radius, as according to the Lanthanide Contraction, of these elements decreases as the atomic number increases.

The Lanthanide Contraction is the result of a poor shielding effect of the 4f electrons. The shielding effect is described as the phenomenon by which the inner-shell electrons shield the outer-shell electrons so they are not effected by nuclear charge. So when the shielding is not as good, this would mean that the positively charged nucleus has a greater attraction to the electrons, thus decreasing the atomic radius as the atomic number increases. The S orbital has the greatest shielding while F has the least and P and D in between the two with P being greater than D. 

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Answered by  | 3rd Mar, 2011, 10:40: AM

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