Question

The elements of 3d transition series are given as: $Sc,Ti,V,Cr,Mn,Fe,Co$ .
Answer the following:
(i) Write the element which shows the maximum number of oxidation states. Give reasons.
(ii) Which element has the highest m.p.?
(iii) Which element shows only +3 oxidation state?
(iv) Which element is a strong oxidising agent in +3 oxidation state and why?

Answer 1

Hint: The number of oxidation states increase till manganese when moved across the 3d subshell. The element that has a strong intermetallic bond has a high melting point. The element that has a total of 3 valence electrons can show only +3 oxidation state. The element which on reduction can attain a stable electronic configuration acts as a strong oxidising agent.

Complete answer:
Let us solve the sub questions one by one giving proper reasons.
(i) The element that shows the maximum number of oxidation states is Manganese (\[Mn\] ). Manganese exists in 6 different oxidation states i.e. from +2 to +7. This is the highest number for any element in the 3d-series. The reason for the existence of such a huge number of oxidation states in manganese is due to the presence of 5 unpaired electrons in its 3d subshell which can show easy transitions.
(ii) Chromium has the highest melting point because it has a half-filled stable d-orbital and these unpaired electrons form strong intermetallic bonds which are difficult to break immediately.
(iii) Scandium has a total of only 3 electrons in its outermost shell and thus can exist only in +3 oxidation state.
(iv) Manganese acts as a strong oxidising agent in its +3 oxidising state as on reduction it attains the +2 state and becomes half filled stable. Thus, in order to attain a half filled stable electronic configuration, manganese acts as a very strong oxidising agent.

Note:
The common error that most of the students commit in this question is that the melting point of manganese is highest due to the presence of five unpaired electrons. But, this is wrong. There is an absence of intermetallic bonds in manganese which makes chromium as the element with highest melting point among the series of elements.