Question

What is meant by the transition elements? Write their general electronic configuration.

Answer 1

There are many different definitions of transition elements. According to IUPAC definition transition metal is an element whose atom has a partially filled d-orbital or subshell. According to scientists, a transition metal is a metal of d-block that contains $3$ to $12$ groups in the periodic table.

Complete answer: According to IUPAC, a transition metal or element is the element that has the ability to form stable cations with an incompletely filled d-orbital or subshell. Generally, the elements which belong to the groups $3$ to $12$ are considered as transition elements. The f-block elements or groups such as lanthanides and actinides are also considered as transition elements. But they have incompletely filled f-orbitals, so they are commonly known as inner transition elements. Some elements are also there which are not transition elements such as mercury, cadmium, and zinc because their electronic configurations are $\left( {n - 1} \right){d^{10}}$. It means they have completely filled d-orbitals. The general electronic configuration of the transition elements are $\left( {n - 1} \right){d^{10}}n{s^{1 - 2}}$. We also see that some of the transition elements have electronic configuration $\left( {n - 1} \right){d^5}n{s^1}$ or $\left( {n - 1} \right){d^{10}}n{s^1}$ due to the stability provided by the half-filled and fully filled electron orbitals.

Note:
It can also be seen that many transition elements do not follow Aufbau principle because of the relatively low energy gap between $3d$ and $4s$ orbitals, and also the $4d$ and $5s$ orbitals. The transition elements also form colored compounds due to the d-d transition of electrons. Due to the unpaired electrons in the d-orbital, these elements also form paramagnetic compounds.