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8.7 What is lanthanoid contraction? What are the consequences of lanthanoid contraction?

On moving along the lanthanoid series, the atomic number is gradually increased by one. It means the number of electrons and protons in the atom is also increasing by one. And because of it, the effective nuclear charge increases (electrons are adding in the same shell, and the nuclear attraction overcomes the interelectronic repulsion due to the addition of a proton). Also, with the increase in atomic number, the number of electrons in orbit also increases. Due to the poor shielding effect of the electrons, the effective nuclear charge experienced by an outer electron is increased, and the attraction of the nucleus to the outermost electron is also increased. As a result, there is a gradual decrease in atomic size with an increase in atomic number. This is known as lanthanoid contraction.

Consequences of Lanthanoid Contraction:

  • Similarities in the properties of second and third transition series
  • Separation of lanthanoid can be possible due to LC.
  • Due to LC, there is variation in basic strength of hydroxide of lanthanoid. (basic strength decreases from La(OH)_{3}-Lu(OH)_{3}).

 

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Posted by

manish

8.7 Which is a stronger reducing agent Cr^{2+} or Fe^{2+} and why ?

 

Cr+2 is a better reducing agent as compared to Fe+2, as this can be explained on the basis of standard electrode potential of Cr+2 (-0.41) and  Fe+2 (+0.77). 

 It can also be explained on the basis of their electronic configuration achieved. Cr+2 obtained d3 configuration whereas Fe+2 gets d5 configuration upon reduction. It is known that d3 is more stable than d5. So Cr+2 is a better reducing agent as compared to Fe+2.

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Posted by

Devendra Khairwa

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