Question

B. What is the electron configuration of an isolated Fe3+ cation?
(Use notation like [Ne]3s^23p^6 for your answer)

i put

[Ar]4s^23d^3

but i got it wrong
i don't know why

Answer 1

Ar is 18. Fe neutral atom is 26.
Ar 3d^6 4s2 = 18 + 8 = 26

Now remove the OUTSIDE 3 electrons.
We take away the 4s2 and 1 of the 3d to make [Ar] 3d^5 which is 18 + 5 = 23 and the Fe^+3 is 26-3=23.