Question

There is irregularities in electronic configuration of actinoids

Answer 1

Dear student,

The 14 elements from atomic number 90 Thorium to atomic number 103 lawrencium are called the actinide elements. However the electronic structures of actinides do not follow the simple pattern found in the lanthanides.

Immediately after La the 4f orbital become lower in energy than 5d orbitals. So in lanthanides electron fills in a regular way. Whereas in case of actinides after Ac the 5f orbital would become lower in energy than 6d. For the first four actinide elements Th ,Pa,U and Np the difference in energy between 5f and 6d is small, so in these elements electron will occupy 5f or 6d levels or both. Later in actinides 5f orbital do become appreciably lower in energy . Thus from Plutonium onwards the 5f shell fills in a regular way, and the element becomes similar. This is why there is an irregularity in electronic configuration of actinides.


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