Question

A.Why do transition elements show variable oxidation states?
B.Name the elements showing maximum number of oxidation states among the first series of transition metal from ${\text{Sc }}\left( {{\text{Z}} = 21} \right){\text{ to Zn}}\left( {{\text{Z}} = 30} \right)$
C.Name the elements which show only $+ 3$ oxidation state.
D.What is lanthanoid contraction? Name an important alloy which contains some of the lanthanoid metals.

Answer 1

The element with vacant orbitals can show multiple oxidation states. The maximum number of oxidation states is shown by the element that lies at the centre of the series. The element at the starting of the series shows only $+ 3$ oxidation state. Lanthanoid contraction occurs in case of f block elements.

Complete step by step answer:
A.D block elements are those elements in which the last electron goes to the d orbital. D block elements have vacant orbitals in which electrons can get excited. This will allow them to change or show the different oxidation state depending upon the type of species with which it will attach.

B.The maximum number of oxidation states, among the first series that is 3 d series, is shown by the manganese. This is because manganese has maximum unpaired electrons that are 5 in its valence shell.

C.The very first element of the 3d series that is Scandium shows only one oxidation state that is $+ 3$.

D.Lanthanide contraction occurs due to an increase in atomic number. As the Lanthanide contraction increases the atomic size the atomic size of tri positive ions decreases. Lanthanides are also named as rare earth elements. They are the elements with atomic number 58 to 71. They belong to f block elements. F block elements are those elements in which the last electron goes to the anti penultimate shell.
The gradual decrease in atomic size occurs as the atomic number increases and this phenomenon is known as lanthanide contraction. This lanthanide contraction brings change in atomic size, difficulty in separation of lanthanides, effect on the basic strengths of lanthanides, their tendency to form complexes and the ionization energy of d block elements. An important alloy formed out of lanthanoid is Mischmetal. It contains about ninety five percent of lanthanide.

Note:
According to IUPAC d block elements are those elements which have partially filled d orbital or have the ability to form partially filled d orbitals in their most stable oxidation state.