Question

What are transition elements? Write any four characteristic properties of transition metals.

Answer 1

Hint: The elements placed in the d-block of the periodic table are referred to as transition elements. However, all d-block elements are not transition elements due to their electronic configuration. The elements placed in f-block i.e lanthanides and actinides are also referred to as inner transition elements.

Complete answer: Those elements which consist of partially filled d-orbitals and have a tendency to show variable oxidation states are known as transition elements i.e., in the modern periodic table, groups $3 - 11$ are termed transition elements.
Although being placed in d-block, the group $12$ elements are not considered as transition elements because at the ground state electronic configuration of these elements have completely filled d-orbitals. The d-block elements are further divided into four categories which are as follows:
First transition series or 3d series: The elements from scandium (atomic number $ = 21$) to copper (atomic number $ = 29$) have a general electronic configuration as $[Ar]3{d^{(1 - 9)}}4{s^2}$. Because, each element adds an electron in its third d-orbital. Hence, these elements are termed as 3d series or first transition series.
Second transition series or 4d series: The elements from yttrium (atomic number $ = 39$) to silver (atomic number $ = 47$) have a general electronic configuration as $[Kr]4{d^{(1 - 9)}}5{s^2}$. Because, each element adds an electron in its fourth d-orbital. Hence, these elements are termed as 4d series or second transition series.
Third transition series or 5d series: The elements from lanthanum (atomic number $ = 57$) to gold (atomic number $ = 79$) have a general electronic configuration as $[Xe]5{d^{(1 - 9)}}6{s^2}$. Because, each element adds an electron in its fifth d-orbital. Hence, these elements are termed as 5d series or third transition series.
Fourth transition series or 6d series: The elements from actinium (atomic number $ = 89$) to roentgenium (atomic number $ = 111$) have a general electronic configuration as $[Rn]6{d^{(1 - 9)}}7{s^2}$. Because, each element adds an electron in its sixth d-orbital. Hence, these elements are termed as 6d series or fourth transition series.
The characteristic properties of transition metal are as follows:
1. Transition metals have a tendency to show variable oxidation states.
2. Mostly 3d metals participate in coordinate bonding to form complexes.
3. Complexes formed using transition metal elements are often paramagnetic in nature.
4. Transition metals have high melting and boiling points.

Note:
It is important to note that due to partially filled d-orbital, most of the complexes formed by transition metals are coloured. This is because, in the presence of ligands the d orbitals of transition elements split into two different sets of orbitals due to which there is an emission or absorption of energy which falls in the visible region. Hence, transition metals form coloured complexes.