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d-and f-Block Elements: Short questions and answers




Question 1. Why are d-block elements called transition elements?
Answer. d-block elements are the elements present between s- and p-block elements. These are called transition elements because they show transition (change) in properties on moving from s-block elements to p-block elements in periodic table. For example, metallic properties of elements change to non-metallic passing through transition elements.

Question 2:Why do the d-Block elements show different oxidation states?
Answer:
Transition elements show different oxidation states in their compounds. Explanation is very simple. These elements have several ns and (n-1) d electrons for bond formation.  Due to small  energy gap between ns and (n-1) d orbitals, all electrons present in these orbitals can participate in chemical bonding.

Question 3.Why does Mn show the maximum oxidation number of oxidation state in 3d series?
Answer.
Ability of transition element to show variable valency depends upon the number of unpaird electrons in (n-1) d orbital that is closer to ns orbital. As there are maximum number of unpaired electrons (i.e.5) present in 3d orbital of Mn. So, it shows maximum number of oxidation states. Oxidation states of Mn are +2, +3, +4, +5, +6 and +7.

Question 4: what is the difference between double Salts and coordination are complex compounds?
Answer. 
Following are main differences between double salt and coordination compound.
Double salt
It is composed of two salts in equal proportion.
It exists only in solid state at room temperature.
It does not retain its identity in aqueous form.
It is an ionic compound and has only ionic bonds
e. g. Potash alum, K2SO4. Al2(SO4)3.24H2O
Coordination compound
It is composed of a central metal ion surrounded by molecules or ions (ligands).
It can exist in solid as well as in aqueous form.
It does not lose its its identity in aqueous form.
Since, it is coordination compound and may or may not contain ionic bond while its complex part has coordination bond or bonds.
e.g. K4[Fe(CN)6] 

Question 5: Explain the following terms.
a. Ligand b. Coordination sphere c. Central metal.
Answer:
a. Ligand
An atom, ion or neutral molecule which surrounds the central metal atom or ion by donating the electron pair is known as ligand.
Example: In K3[Fe(CN)5] and Na3[FeCl6], CN and Cl are ligands
b. Coordination Sphere:
The central neutral atom or ion with ligand is called coordination sphere. It is usually placed in the square bracket. The central atom may be positively charged, negativity charged or neutral.
Example: In K3[Fe(CN)5] and Na3[FeCl6], [Fe(CN)5] and [FeCl6] are coordination spheres.
c. Central metal atom or ion
A metal atom or ion surrounded by ligands in a coordination sphere is called central metal atom or ion.
Example: In [Fe(CO)5 ], Fe is a central metal atom while in Na3[MnCl6], Mn is central metal ion.


Question 6: How are dichromate converted in chromate ion?
Answer:
Both dichromate and chromate are in equilibrium with each other at pH =4.


When small amount of a base is added to above equilibrium mixture, OH- from base reacts with H+ to produce H2O and concentration of H+ is decreased. According to Le-chatleir principle, equilibrium will be shifted in reverse direction and orange chromate ions will be converted into yellow chromate ion.

Question 7: What is the difference between paramagnetic and diamagnetism?
Answer:
Paramagnetic is a behavior of a material by which it is attracted by external magnetic field. This is due to presence of unpaired electrons in these materials. For example, Fe, Mn, Cr etc
Diamagnetism is a behavior of a material by which it is slightly repelled by external magnetic field. This is due to presence of paired electrons in these materials. For example, Zn, Au, Hg etc
Question 8: What are advantages of potassium dichromate in titration?
Answer. 
As an oxidant, potassium dichromate (K2Cr2O7) has following advantages.
i. It can be used as a primary standard as it can be obtained in high purity. So, a stable aqueous solution of known concentration can be prepared directly from weighing it .
ii. It can be used in presence of chloride ion without side reactions, provided that chloride ions are not in very high concentration.
iii. Its aqaous is not attacked by oxidizeable impurities like rubber and other organic impurities.


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