Q. 23

A) I) What are th

Answer :

I) In the lanthanoids series, the general and most common oxidation state is +3, while they can also form +2 and +4 oxidation states. This variation in the formation of oxidation states is due to the extra stability of empty, half-filled or filled f-orbitals.

II) Transition elements are those elements which have partially filled d-orbitals in their ground state or in their ions. The general electronic configuration of these elements is represented as . These elements show mixed properties of both s and p block elements. They are less electropositive than s-block elements while more electropositive than p-block elements. They form colored compounds and have high melting and boiling points.


III) Elements like Zn, Cd and Hg are not included in the regular transition elements. This is due to the fact these elements have completely filled d-orbitals in their ground state. As transition elements are defined as those elementswhich have partially filled d-orbitals in their ground state or in their ions.Thus, Zinc or Cadmium are not considered as Transition elements.


OR


i) Electronicconfiguration of is.


EC of is .


The completely filled or partially filled orbitals are more stable than others. Therefore, from the EC of both the ions, it can be inferred that has half-filled 3d electrons as compared to ion. Thus, is not get easily oxidised to while being less stable it gets readily oxidised to


ii) Atomization is the process of breaking a big molecule into fine particles. The extent to which metallicbonding for an element undergoes is the deciding factor for the atomization enthalpy. The stronger is the metallic bonding of an element, the more will be the atomization enthalpy. In all transition metals, except for the Zinc, (EC: ),they have unpaired electrons that account for strongermetallic bonding. Due to the absence of these unpaired electrons, theinter-atomic electronic bonding is the weakest in Zn and as a result,it has the least enthalpy of atomization.


iii) is colorless in aqueous solution whereas is colored. It is because of the absence of d-d transition in case of Scandium, while in the case of Titanium, d-d transition is possible. The Titanium ion has 1 electron in its 3d orbital which makes the transition possible whereas Scandium has no electrons in its 3d orbital.


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