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Inorganic chemistry carries a bit low weightage as compared to organic and physical chemistry in JEE Mains question paper. But it is this section which is considered to be very easy, scoring and less time taking by the test takers. The biggest advantage of this section is that maximum number of times, it is directly from NCERT. Thus, all JEE Main test takers advise to consider NCERT as bible for inorganic chemistry. Read preparation tips for JEE Main Chemistry
|d & f block||2||1||2|
Read the article to find necessary preparation notes on d & f block elements that will help you build a strong base in this section.
The elements in which the last differentiating electron enters into the d-orbitals of the penultimate shell i.e. (n–1) d where n is the last shell are called d-block elements. A transition element may also be defined as the element which partially filled d-orbital in their ground state or most stable oxidation state.
Cu (Z = 29) = 1s2 2s2 2p6 3s2 3p6 3d10 4s1
Cu2+ = 1s2 2s2 2p2 3s2 3p6 3d9
The properties of these elements are intermediate between the properties of s-block and p-block elements.
These elements represent a change or transition in properties from more electropositive elements (s-block) to less electropositive elements (p-block). Therefore these elements are called transition elements.
The position of d-block element has been shown in periodic table as follows :
(1) In d-block elements with increase in atomic number, the d- orbitals of penultimate shells i.e. (n-1) d are gradually filled by electrons. The general electronic configuration of d- block element is (n-1)d1–10.ns0, 1, 2.
(2) Depending upon the d-orbitals of which penultimate shell i.e. n = 4, 5, 6, 7 are filled, four rows (called series) os ten elements each obtained. They correspond to 3d, 4d, 5d and 6d subshells.
(3) Energy of ‘(n–1)d’ subshell is slightly greater than ‘ns’ subshell, hence the orbital is filled first then (n – 1) d orbitals.
(4) The general electronic configuration of d-block/d-series elements be shown as follows:
Except for mercury which is a liquid, all the transition elements have typical metallic structure. They exhibit all the characteristics of metals. ductile, have high melting and boiling points, high thermal and electrical conductivity and high tensile strength.
Transition metals have high melting points which is due to their strong metallic bond.
f –block elements are also called inner transition elements. In these the last electron enters penultimate i.e. (n – 2)f f orbital. The differentiating electron in transition elements may enter either 4f or 5f orbitals based upon which they are differentiated into lanthanides and actinides.
Lanthanides: In lanthanides the differentiating electron enters 4f orbital. These are cerium to lutetium. The name lanthanides is because they come immediately after lanthanum.
Actinides: In actinides the differentiating electron enters 5f orbitals. These are thorium to lawrencium. These elements come immediately after actinium.
Electronic configuration: General electronic configuration of f – block elements is (n–2)f1–14(n–1)d0–1ns2
Ques. Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why ?
Ans. Manganese (Z = 25), as it atoms has the maximum number of unpaired electrons.
Ques. Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number ?
Ans. In transition elements, there are greater horizontal similarities in the properties in contrast to the main group elements because of similar ns2 common configuration of the outermost shell.
An examination of common oxidation states reveals that accepts scandium, the most common oxidation state of first row transition elements is +2 which arises from the loss of two 4s electrons. This means that after scandium, d-orbitals become more stable than the s-orbital.
Further, +2 state becomes more and more stable in the first half of first row transition elements with increasing atomic number because 3d orbitals acquire only one electron in each of five 3d orbitals (i.e. remains half filled) and electronic repulsion is the least and nuclear charge increases. In the 2nd half of first row transition elements, electrons start pairing up in 3d orbitals. (Ti2+ to Mn2+ electronic configuration changes from 3d2 to 3d5 but in 2nd half i.e. Fe2– to Zn2+ it changes from d6 to d10)..
Ques. What are the characteristics of the transition elements and why are they called transition elements ? Which of the d-block elements may not be regarded as the transition elements?
Ans. The important characteristics of transition metals are:
(i) All transition elements are metallic in nature, e.g., all are metals.
(ii) These metals exhibit variable oxidation states.
(iii) Transition metal atoms or ions generally form the complexes with neutral, negative and positive ligands.
(iv) Compounds of transition metals are usually coloured.
(v) The compounds of these metals are usually paramagnetic in nature.
(vi) Transition metals and their compounds act as good catalysts, i.e., they show catalytic activities.
(i) These metals form various alloys with other metals of the series.
(ii) These metals form interstitial compounds with C, N, B and H.
Ques. On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not ?
Ans. On the basis of incompletely filled 3d orbitals in case of scandium atom is its ground state (3d1), it is regarded as a transition element. On the other hand, zinc atom has completely filled d orbitals (3d10) in its ground state as well as in its oxidised state, hence it is not regarded as a transition element.