(1) Why do transition elements show variable oxidation states?(2) Name the element showing maximum number of oxidation states among the first series of transition metals from Sc(Z=21) to Zn(Z=30).(3) Name the element which shows only +3 oxidation state.

Answer:

(1) Transition elements (also known as transition metals) are elements that have partially filled d orbitals. IUPAC defines transition elements as an element having a d subshell that is partially filled with electrons, or an element that has the ability to form stable cations with an incompletely filled d orbital. The electronic configuration of transition element is (n-1)d⁵ ns¹ or (n-1)d¹⁰ ns¹.

These elements show variable oxidation state because their valence electrons in two different sets of orbitals, that is (n-1)d and ns. The energy difference between these orbitals is very less, so both the energy levels can be used for bond formation. Thus, transition elements have variable oxidation states.

(2) Mn(Z-25) has the highest number of unpaired electrons in the d-subshell and it shows high oxidation state(+7).

(3) Scandium (Sc) only exhibits a +3 oxidation state in these series.