Question

Why Thorium(90) has an exceptional electron configuration?​

Answer 1

Answer :

Thorium  ( Th₉₀ )     .: Z=90

According to Aufbau Principle ,

The difference in energy between 5f and 6d orbitals is small. Thus in elements electrons may occupy the 5f or 6d levels or sometimes both.

Later in actinide series the 5f do become appreciable lower in energy, thus from Pa onward the 5f shells fill in regular way.

This is much Similar to Chromium & Copper.

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