In the transition series, the elements Iron (), Cobalt (), and Nickel () collectively exhibit almost — d and f Block Elements Chemistry Question
Question
In the $3d$ transition series, the elements Iron ($Fe$), Cobalt ($Co$), and Nickel ($Ni$) collectively exhibit almost identically plateaued atomic radii. Determine the precise atomic number ($Z$) of the specific element within this localized triad ($Fe, Co, Ni$) that inherently possesses the mathematical maximum number of unpaired $d$ -electrons in its neutral ground state.
💡 Solution & Explanation
The elements are $Fe$ ($Z=26$), $Co$ ($Z=27$), and $Ni$ ($Z=28$). Their electronic configurations are $[Ar] 3d^6 4s^2$, $[Ar] 3d^7 4s^2$, and $[Ar] 3d^8 4s^2$, respectively. According to Hund's rule, $Fe$ has $4$ unpaired electrons, $Co$ has $3$, and $Ni$ has $2$. Iron possesses the maximum number of unpaired electrons among the three, and its atomic number is $26$.