# What is the electron configuration of d-block ions, for example V+?

Mar 25, 2016

EXAMPLE: TYPICAL TRANSITION METAL

If we start from vanadium atom, it is easier to think about.

Since $\text{V}$ is atomic number $23$, it is on the third column (and fourth period) of the transition metal series and has three $3 d$ electrons.

Using the noble gas configuration, we reference the previous noble gas, which is $\text{Ar}$, and get

$\textcolor{g r e e n}{\left[A r\right] 3 {d}^{3} 4 {s}^{2}}$.

Since the $3 d$ orbital is lower in energy to a significant extent on the first-row transition metals after $\text{Sc}$, we would remove electrons from the $4 s$ orbital first upon ionization of $\text{V}$ into ${\text{V}}^{+}$.

In fact, the orbital potential energies are $\text{V"_(4s) = -"7.32 eV}$ and $\text{V"_(3d) = -"10.11 eV}$, and clearly, ${\text{V"_(3d) < "V}}_{4 s}$.

The ionization can be written as follows:

${\text{V" -> "V}}^{+} + {e}^{-}$

Thus, the electron configuration for ${\text{V}}^{+}$ is reasonably predicted to be

$\textcolor{b l u e}{\left[A r\right] 3 {d}^{3} 4 {s}^{1}}$,

but it is not reasonable to predict:

$\textcolor{red}{\left[A r\right] 3 {d}^{2} 4 {s}^{2}}$.

The actual observed result is $\left[A r\right] 3 {d}^{4}$. (It may be because the removal of the $4 s$ electron reduces repulsions enough that the $4 s$ orbital sufficiently lowers in energy, so that the electron favors being in the $3 d$ orbital for this particularly unpaired configuration.)

EXAMPLE: ATYPICAL TRANSITION METAL

In general you should be asked for electron configurations of transition metals that follow the trend of the $n s$ being higher in energy than the $\left(n - 1\right) d$, but be aware that that is not always the case.

For instance, yttrium has the electron configuration

$\left[K r\right] 5 {s}^{2} 4 {d}^{1}$,

and in fact, the $4 d$ orbital is higher in energy than the $5 s$. $\text{V"_(5s) = -"6.70 eV}$ and $\text{V"_(4d) = -"6.49 eV}$, so the ionization of $\text{Y}$ is likely to give you the configuration for ${\text{Y}}^{+}$ to be

$\textcolor{b l u e}{\left[K r\right] 5 {s}^{2}}$.

And we indeed see that if we look here for reference.