CBSE Class 12 Chemistry The D And F Block Elements Notes Set B

POINTS TO BE REMEMBERED: ‐‐‐

1. The elements of periodic table belonging to group 3 to 12 are known as d‐Block elements.

2.The general electronic configuration of these elements is (n ‐1)d^1‐10 ns ^1‐2

3.  d‐ Block elements are collectively known as Transition Elements because properties of these elements vary in between s‐Block and p‐Block elements.

4.A transition element should have partially filled (n‐1) d orbital. 

5. Group 12 elements i.e. Zn, Cd, Hg have completely filled (n‐1) d‐orbital in atomic & ionic state & thus these elements are considered as Typical Transition Elements.

6. All these elements are metals. They are less electropositive than s‐block elements & more electropositive than p‐block elements.

7. The atomic radii decreases from group 3 to 6 (i.e. Sc to Cr) because of increase in effective nuclear charge gradually.

8. The atomic radii of group 7,8 9 &10 elements (i.e. Fe,Co,Ni) is almost same because pairing of electrons take place in (n‐1)d orbital causing repulsion i.e. shielding of (n‐1)d orbital.

9. Group 11 &12 elements i.e. Cu & Zn have bigger size due to strong shielding of completely filled (n‐1)d orbital.

10.The transition elements show variable oxidation state due to small energy difference between (n‐1)d &ns orbital as a result both (n‐1)d &ns electrons take part in bond formation.

11.The highest oxidation state of an element is equal to number of unpaired electrons present in (n‐1)d &ns orbital.

12.Transition elements have high enthalpy of atomization/ sublimation Because of large number of unpaired electrons in their atoms, they have stronger interatomic interaction and hence strong metallic bonding is present between atoms.

13.Most of transition elements are paramagnetic due to presence of unpaired electrons in (n‐1) d orbital.

14.Most of transition elements are used as catalyst. It is due to (i) partially filled (n‐1) d orbital (ii) Variable oxidation state (iii) Ability to change oxidation state frequently.

15.Most of transition elements form coloured compounds due to presence of unpaired electrons in (n‐1) d orbital & thus they can undergo d‐d transition.

16.Most of transition elements form complex compounds due to (i) small size (ii) high charge (iii) presence of vacant d‐orbital of suitable energy.

17.Transition elements have lower value of Reduction Potential due to high ionization potential, high heat of sublimation & low enthalpy of hydration.

18.Transition elements form interstitial compounds because size of interstitial voids is similar to size of non‐ metals C, N, O, H.

19. Transition elements form alloys due to similar ionic radii.

20.The oxides of transition metals in lower oxidation state are BASIC, intermediate oxidation state are AMPHOTERIC, highest oxidation state are ACIDIC.

LANTHANOIDS: ‐‐‐

1. The 14 elements after Lanthanum having atomic number 58 to 71 are collectively known as Lanthanoids.

2. The general electronic configuration of these elements is [Xe] 4^f1‐14, 5d^0‐1 ,6s² .

3. Most common oxidation state of these elements is +3, but Ce shows +4, Eu +2, because they acquire stable configuration.

4. The size of Lanthanoids and its trivalent ion decreases from La to Lu due to poor shielding of 4f electrons. It is known as lanthanoids contraction.

ACTINOIDS:

1.The 14 elements after Actinium having atomic number 90 to 113 are collectively known as Actinoids. 

2. The general electronic configuration of these elements is [Rn] 5f1‐14, 6d0‐1 ,7s2.

3. The size of actinoids and its trivalent ion decreases from Ac to Lw due to poor shielding of 5f electrons. It is known as actinoids contraction.

4. The elements after U (92) are man made known as transuranic elements.

POTASSIUM DICHROMATE:

Preparation: It takes place in three steps‐

(i) Conveorsion of chromite ore to sodium chromate.

(ii) Cnversion of sodium chromate to Sodium dichromate.

(iii) Conversion of sodium dichromate to potassium dichromate

Following reaction take place;-

4 FeCr²O⁴+ 4 Na²CO³ +7O₂ —→  2 Na₂CrO₄+ 2Fe₂O3 +8 CO₂

2Na₂CrO₄ + 2 H+    →   Na₂Cr₂O₇ + 2 Na⁺ + H₂O

Na₂Cr₂O₇ + 2 KCl    →   K₂Cr₂O₇ + 2 NaCl

The chromates and dichromates are interconvertible in aqueous solution depending upon Ph of the solution.

POTASSIUM PERMANGNATE:

Preparation:‐‐

It takes place in two steps:‐

(i) Conversion of pyrolusite ore into potassium magnate

(ii) Conversio of potassium magnate to  potassium permagante

Following reactions tak

2 MnO₂ + 4 KOH + O₂   →  2 K₂MnO₄ + 2H₂O

3 MnO4 ^2‐ +4H⁺   →  2 MnO^4‐ +MnO₂ +2H₂O

QUESTION ANSWERS

(TWO MARK QUESTIONS)

Q.1‐Explain briefly how +2 oxidation state becomes more and more stable in the first half of the first row transition elements with increasing atomic number.

A.1‐In M²⁺ ions, 3d‐orbitals get occupied gradually as the atomic number increases. Since, the number of empty d