When a transition metal forms a positive ion, the electrons are lost first from
Correct answer: D. the 4s subshell
- A. the 3d subshell
- B. the 4p subshell
- C. the innermost shell
- D. the 4s subshell
Explanation
Although 4s fills before 3d, once the d subshell is occupied the 4s level becomes the higher in energy, so it is emptied first on ionisation, and the Fe2+ ion is therefore 3d6 rather than 3d4 4s2. This detail is asked frequently because it appears to contradict the filling order. It explains why almost every transition metal shows a plus 2 oxidation state.
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About Electronic Structure of d-Block Elements
The electronic structure of d-block elements covers the filling of the (n-1)d and ns orbitals, general electronic configurations, and the exceptions shown by chromium and copper. It explains how partially filled d orbitals produce variable oxidation states, coloured ions, magnetic behaviour and complex formation, while distinguishing transition elements from elements with completely filled d subshells.
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