D and F block

• why are d block elements called transition elements

  because their properties are intermediate of s and p block
• give electronic configuration of d block elements

  (Noble gas)(n-1) d 1–10ns 1–2.
• explain exceptional electronic configuration of D block elements

  since energy difference between ns and (n-1)d is less, some d block elements show some exceptional electronic configuration. This is due to extra stability of half filled and completely filled orbitals
• why Zn, Cd and Hg are not regarded as transition elements

  They contain completely filled d-orbitals in ground state as well as ionic state
• metallic character of transition elements

  They can lose valence electrons and form cation. They show metallic properties like high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre
• Mercury is liquid at room temperature, Zn and Cd are soft metals with low melting points. Explain


  Due to the absence of unpaired electrons in Hg, Zn and Cd metallic bond is very weak. Therefore their melting point are less. Hence Hg exists as liquid at room temperature and Zn and Cd are soft
• melting of 3d series are less than 4d and 5d series

  this is due to high enthalpy of atomization in 4d and 5d series than 3d series
• Explain variation of atomic and ionic sizes of transition metals

  Atomic and ionic sizes decrease with increase in atomic number
• 3d series transition metals exhibit +2 as the most common oxidation state(except scandium) why?

  The +2 oxidation state arises from the loss of 2 4s electrons . This means that after scandium, d orbitals become more stable than s orbital.
• name the element in 3d series which shows maximum oxidation state

  manganese( Mn), OS=+7
• name the transition element which does not exhibit variable oxidation states

  Zinc ( Z=30, OS=+2)
• How does ionic character of metal oxides vary with oxidation number?

  lower oxidation state of metal oxide higher the ionic character
• The E*(M2+/M) value for copper is +0.34V. why?

  Cu has high energy of atomization and low hydration energy. The ionisation energy needed is not compensated by hydration energy
• explain paramagnetic property of transition elements

  due to the number of unpaired electrons in d orbital and due to orbital angular momentum and spin momentum of electron. Magnetic moment increases as number of unpaired electrons increases
• explain colour of a transition metal ions

  due to d-d transition

  presence of unpaired electrons
• Zn2+ are colourless. why

  due to absence of unpaired electrons
• Cu2+ salts are coloured. why

  due to presence of unpaired d electrons
• Explain catalytic properties of transition metals

  i. variable oxidation states

  ii. large surface area for adsorption of reactant molecules

  iii. presence of incompletely filled or partially filled d orbitals

  iv. formation of intermediate compounds
• Examples of transition metals as catalyst

  Vanadium pentoxide is used as a catalyst in contact process( manufacture of H2SO4)

  Iron oxide as a catalyst in Habers process( Manufacture of NH3)

  Nickel used as catalyst in hydrogenation of oils.
• V205 is amphoteric oxide. explain

  it reacts with both alkalis and acids
• 2 uses of K2Cr2O7

  used in leather industry

  used as an oxidizing agent
• Potassium dichromate (K2Cr2O7) is prepared from chromite ore FeCr2O4
• Chromite ore is fused with sodium or potassium carbonate in free access of air
• The reaction for the preparation of potassium dichromate is:

  4FeCr2O4 + 8Na2CO3 + 7O2 → 8Na2CrO4 + 2FeO3 + 8CO2
• The yellow solution of sodium chromate is filtered and acidified with sulfuric acid to give a solution from which orange sodium dichromate Na2Cr2O7.2H2O can be crystallized
• The reaction for the formation of sodium dichromate is:

  2Na2CrO4 + 2H+ → Na2Cr2O7 + 2Na+ + H2O
• Sodium dichromate is more soluble than potassium dichromate
• When sodium dichromate is fused with KCl, it forms orange crystals of potassium dichromate
• The reaction for the formation of potassium dichromate from sodium dichromate is:

  Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl
• explain the formation of K2Cr2O7

  .
• How is potassium permanganate manufactured?

  Step 1: Pyrolusite is powdered and fused with KOH in the presence of KNO3 as an oxidizing agent to form potassium manganate

  Step 2: The potassium manganate undergoes disproportionation reaction in acidic or neutral medium to give permanganate
• What are lanthanoids??

  The elements from cerium (Z = 58) to lutetium (Z = 71). In these elements the added electrons enter 4f orbitals
• General electronic configuration of lanthanoids

  [Xe] 4f 1-14 5d 0-1 6s2
• define lanthanoid contraction


  the gradual decrease in atomic and ionic radii from lanthanoid to lutitium is called lanthanoid contraction
• Cause for lanthanoid contraction

  due to imperfect shielding of one electron to another in the same set of orbitals
• 2 consequences of lanthanoid contraction

  The atomic radii of Zr and Hf is almost the same hence they occur together. Hence it is difficult to separate them

  Covalent character of cation increases
• Give composition of Mischmetall and its uses

  Lanthanoid[95%]+ Iron[5%]+ traces of S, C, Ca and Al

  Used in Mg based alloys to produce bullets, shell and lighter flint
• Actinoids show greater number of oxidation states. Why

  Due to comparable energies of 5f, 6d and 7s levels
• Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

  This is because 5f electrons will be less effectively shielded from the nuclear charge than 4f electrons of corresponding lanthanides