Gadolinium belongsd to 4f series. It's atomic number is 64. which of the following is the correct electronic configuration of gadolinium ?

Options

A. `[Xe] 4f^(7) 5d^(1) 6s^(2)`
B. `[Xe] 4f^(6) 5d^(2) 6s^(2)`
C. `[Xe] 4f^(8) 6d^(2)`
D. `[Xe] 4f^(9) 5s^(1)`

Answer

A

Explanation

Lanthanum (the d-block element preceding the lanthanide series) has the electronic structure: `[Xe] 5d^(1) 6s^(2)` . It might be, thus, expectd that the 14 elements form Ce to Lu would be formed by adding 1, 2, 3, … 14 electrons into the 4f level. However, it is energatically favourable to move the single 5d electrom into the 4f level in most of the elements, but not in the cases of Ce, Gd and Lu. The reason why Gd has a `5d^(1)` arrangement is that leaves a half 4f level, which gives increased stability. Other elements with extra stable 4f subshell are: `Eu: ([Xe] 4f^(7) 6s^(2))` `Yb: ([Xe] 4f^(14) 6s^(2))` `Lu: ([Xe] 4f^(14) 5d^(1) 6s^(2))`