Question

Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition elements.

Answer 1

The properties of the elements of the first transition series differ from those of the heavier transition elements in many ways. 
(i) The atomic sizes of the elements of the first transition series are smaller than those of the heavier elements (elements of 2nd and 3rd transition series). However, the atomic sizes of the elements in the third transition series are virtually the same as those of the corresponding members in the second transition series. This is due to lanthanoid contraction. 

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(ii) +2 and +3 oxidation states are more common for elements in the first transition series, while higher oxidation states are more common for the heavier elements. 

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(iii) The enthalpies of atomisation of the elements in the first transition series are lower than those of the corresponding elements in the second and third transition series. 

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(iv) The melting and boiling points of the first transition series are lower than those of the heavier transition elements. This is because of the occurrence of stronger metallic bonding (M-M bonding). 

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(v) The elements of the first transition series form low-spin or high-spin complexes depending upon the strength of the ligand field. However, the heavier transition elements form only low-spin complexes, irrespective of the strength of the ligand field.

Answer 2

The elements of the first transition series (Scandium to Zinc) possess several distinct properties compared to their heavier counterparts in the second and third transition series. This differentiation can be attributed to several factors:

1. Atomic and Ionic Sizes:
  - The atomic and ionic radii of the first transition series elements are generally smaller compared to the heavier transition elements. This results in higher charge density and stronger metallic bonding, leading to higher melting and boiling points.

2. Ionization Energies:
  - First transition series elements tend to have higher ionization energies due to their smaller atomic sizes. This makes them less reactive in some cases compared to heavier transition elements.

3. Oxidation States:
  - The first transition series elements typically exhibit a wider range of oxidation states. For example, manganese can show oxidation states from +2 to +7. The heavier elements, however, often exhibit fewer oxidation states due to the increased energy required to remove additional electrons.

4. Complex Formation:
  - The first transition series elements form a variety of complex ions, often with high coordination numbers. The heavier elements, particularly those in the third transition series, tend to form more stable complexes due to their larger atomic size and lower charge density.

5. Magnetic Properties:
  - Many of the first transition series elements (like iron, cobalt, and nickel) show significant magnetic properties due to the presence of unpaired electrons. Heavier transition elements may have paired electrons in their d-orbitals, leading to different magnetic behaviors.

6. Electronegativity:
  - The electronegativity of the first transition series elements is generally higher than that of the heavier elements, influencing their chemical reactivity and the type of compounds they form.

7. Catalytic Properties:
  - Elements of the first transition series are often used as catalysts in industrial processes due to their ability to adopt multiple oxidation states and form stable intermediates. Heavier transition elements are also used as catalysts but tend to form different types of catalytic systems.

8. Coordination Chemistry:
  - First transition series elements often form more stable and diverse coordination compounds. Heavier transition metals, due to their larger size, can form complexes with higher coordination numbers but these complexes may not always be as stable.

9. Ligand Field Stabilization Energy (LFSE):
  - LFSE is generally more pronounced in the first transition series due to their smaller size and higher charge density, leading to stronger field interactions. This affects their color, magnetic properties, and stability of complexes differently from the heavier elements.

In summary, while both the first and heavier transition series elements share core transition metal characteristics, differences in atomic size, ionization energy, electronegativity, and electron configuration lead to varied properties and behaviors.