Question

(i) Name the elements of the \[3d\] transition series which shows maximum number of oxidation states. Why does it show so?
(ii) Which transition metal of $3d$ series has positive \[E_{\left( {{M^{2 + }}/M} \right)}^\circ \] value and why?
(iii) Out of $C{r^{3 + }}$ and $M{n^{3 + }}$, which is a stronger oxidizing agent and why?
(iv) Name a member of the Lanthanoid series which is well known to exhibit $ + 2$ oxidation state.
(v) Complete the following equation $MnO_4^ - + 8{H^ + } + 5{e^ - } \to $

Answer 1

Hint: d-block elements are the elements which can be found form the third group to the twelfth group of the modern periodic table. The valence electrons of these elements fall under the d-orbital, d-block elements are also referred to as transition elements or transition metals.


Complete step by step answer:
(i) In $3 - d$ series of transition metals manganese has an atomic number of $25$ that gives the electronic configuration as $\left[ {Ar} \right]3{d^5}4{s^2}$, where we can see the maximum no. of oxidation no. unpaired electrons are also found in manganese atom, so it can show a maximum oxidation state of $ + 7$.
(ii) Copper is a transition metal of $3d$ series that exhibits positive $Mno_4^ - + 8{H^ + } + 5{e^ - }$ value of a metal, it depends on the energy changes involved in the following.
1. Sublimation energy: The energy required for converting one mole of an atom from solid state to gaseous state.
${M_{\left( s \right)}} \to {M_{\left( g \right)}},\Delta H({\text{Sublimation}}) = high$
2. Ionization energy: The energy required to take out electrons from one mole of atom in the isolated gaseous state.
\[{M_{\left( g \right)}} \to M_{\left( g \right)}^ + + {e^ - },\Delta H(ionisation) = high\]
3. Hydration energy: The energy released when one mole of ions are hydrated.
\[M + {H_2}O \to M.{H_2}O,\Delta H\left( {hydration} \right) = low{\text{ }}energy\]
Since, the copper has high energy of ionization, sublimation and low hydrate on energy.
The \[E_{\left( {{M^{2 + }}/M} \right)}^\circ \] value of copper is positive.
(iii).Out of \[C{r^{3 + }}\] and \[M{n^{3 + }},\] $M{n^{3 + }}$ is stronger oxidizing agent because it has $4$ electrons in its valence shell and when it gains one electron to form $M{n^{2 + }}$, it results in half filled $\left( {{d^5}} \right)$ configuration that has extra stability.
(iv). Europium $\left( {Eu} \right)$ is well known to exhibit $ + 2$ oxidation state due to its half filled orbital in $ + 2$ oxidation state.
(v). $MnO_4^ - + 8{H^ + } + 5{e^ - } \to M{n^{2 + }} + 4{H_2}O$


Note:
There are total $40$ d-block elements which are also known as transition metals.The f-block lanthanide and actinide series are also considered transition metals and are called "inner transition metals".