Which first-row transition metal has the most unpaired electrons?

Aug 20, 2017

Chromium. Is it also the most paramagnetic? Why or why not?

The only candidates would be in the center of the transition metals, i.e. the ones with close to five $3 d$ electrons ($\text{Cr", "Mn", "Fe}$).

Iron has the electron configuration:

$\left[A r\right] {\overbrace{3 {d}^{\textcolor{red}{4}}}}^{\text{unpaired" overbrace(3d^2)^" already paired}} 4 {s}^{2}$

$\underbrace{\underline{\uparrow \downarrow} \text{ "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" } \underline{\uparrow \textcolor{w h i t e}{\downarrow}}}$
$\text{ "" "" "" "" "" "" } 3 d$

$\underline{\uparrow \downarrow}$
$4 s$

Manganese has the electron configuration:

$\left[A r\right] {\overbrace{3 {d}^{\textcolor{red}{5}}}}^{\text{unpaired}} 4 {s}^{2}$

$\underbrace{\underline{\uparrow \textcolor{w h i t e}{\downarrow}} \text{ "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" } \underline{\uparrow \textcolor{w h i t e}{\downarrow}}}$
$\text{ "" "" "" "" "" "" } 3 d$

$\underline{\uparrow \downarrow}$
$4 s$

But chromium has...

$\left[A r\right] {\overbrace{3 {d}^{\textcolor{red}{5}} 4 {s}^{\textcolor{red}{1}}}}^{\text{unpaired}}$

$\underbrace{\underline{\uparrow \textcolor{w h i t e}{\downarrow}} \text{ "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" } \underline{\uparrow \textcolor{w h i t e}{\downarrow}}}$
$\text{ "" "" "" "" "" "" } 3 d$

$\underline{\uparrow \textcolor{w h i t e}{\downarrow}}$
$4 s$

$6 > 5 > 4$, so...