Question

What is the electronic configuration of the first-row transition metals and their dictations? Why is the configuration of $C{r^{ + 2}}$ unusual?

Answer 1

Transition metals means the chemical elements that belong to d-block and have incomplete d-orbital electronic configuration. First row transition series are $3d$ row elements. They undergo oxidation and form di cations, but chromium due to half filled configuration does not form usually.

Complete Step By Step Answer:
Periodic table consists of four blocks namely s, p, d, and f blocks. The d-block has three series namely $3d,4d,$ and $5d$ series.
The general electronic configuration of first row transition series is $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^n}$
When these elements undergo oxidation means loss of electrons and forms a di cation.
The general electronic configuration of the di cations of first row transition series is ${\left( {1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^n}} \right)^{ + 2}}$
Chromium is the element with atomic number $24$ and has five valence electrons in its valence shell. Its configuration is deviated by normal electronic configuration of first row transition series due to its stable half-filled electronic configuration.
The electronic configuration of chromium is $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^1}3{d^5}$
Due to the above configuration, chromium undergoes loss of one electron in general and forms $C{r^ + }$ but not $C{r^{ + 2}}$ .
Thus, though the first-row transition metals form dictations, the formation of $C{r^{ + 2}}$ is not usual.

Note:
Copper and chromium are the chemical elements that belong to the first row transition series and deviated from the general electronic configuration of first row transition series. These two elements have half-filled and completely filled electronic configuration. Thus, these two elements deviate the configuration and do not form a di cation usually.