what is meant by lanthanoid contraction and actinoid contraction ?

Asked by pooja dev | 30th Nov, 2010, 12:00: AM

Expert Answer:

In lanthanides there is a gradual increase in atomic size, atomic radii and ionic radii with increase in atomic number. This regular decrease is known as lanthanide contraction.
Causes:In lanthanides, the nuclear charge increases by one unit at each successive element and this new electron enters the 4f-subshell. Due to the peculiar shapes of f-orbitals, there is imperfect shielding of electrons from the nuclear attraction. As a result of this the size of lanthanide atoms decreases.
In actinoid there is a gradual increase in atomic size, atomic radii and ionic radii with increase in atomic number. This regular decrease is known as actinoid contraction.
Causes:In actinoid, the nuclear charge increases by one unit at each successive element and this new electron enters the 5f-subshell. Due to the peculiar shapes of f-orbitals, there is imperfect shielding of electrons from the nuclear attraction. As a result of this the size of actinoids atoms decreases.

Answered by  | 30th Nov, 2010, 07:46: PM

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