D And F Block Elements

1. Fe (Iron, Z=26):
Neutral Fe: [Ar] 3d 4s .
Fe (remove 2 from s, 1 from d): [Ar] 3d .
Hund's rule: 5 electrons in 5 d-orbitals 5 unpaired electrons.
2. Zn (Zinc, Z=30):
Neutral Zn: [Ar] 3d 4s .
Zn (remove 2 from s): [Ar] 3d .
All electrons paired 0 unpaired electrons.
3. Mn (Manganese, Z=25):
Neutral Mn: [Ar] 3d 4s .
Mn (remove 2 from s): [Ar] 3d .
Hund's rule: 5 electrons in 5 d-orbitals 5 unpaired electrons.

1. Cu Configuration: Copper (atomic number 29) has configuration [Ar] 3d 4s . Cu is [Ar] 3d .
It has one unpaired electron in the d-orbital. This allows for d-d transitions (movement of electron between split d-orbitals) by absorbing visible light, resulting in colour.
2. Zn Configuration: Zinc (atomic number 30) has configuration [Ar] 3d 4s . Zn is [Ar] 3d .
The d-subshell is completely filled. There are no empty d-orbitals for electron transition. Hence, no visible light is absorbed, and the salts appear colourless (white).

1. Oxidation States: Lanthanoids show +3 as the dominant oxidation state, with occasional +2 or +4. Actinoids show a wider range of oxidation states (+3, +4, +5, +6, +7) due to comparable energies of 5f, 6d, and 7s shells.
2. Binding Energy: 4f electrons (Lanthanoids) have higher binding energy and are more deeply buried. 5f electrons (Actinoids) have lower binding energy and are more available for bonding (covalent character).
3. Radioactivity: Only Promethium is radioactive among Lanthanoids. All Actinoids are radioactive.

1. Transition metals have very similar atomic sizes (radii) within a series (e.g., Cr, Mn, Fe, Co, Ni).
2. Because the atoms are of similar size, atoms of one metal can easily replace the atoms of another metal in its crystal lattice without disrupting the structure significantly.
3. This ready substitution allows the formation of solid solutions or alloys (like Brass, Bronze, Steel) which are hard and have high melting points.

1. Zirconium (Zr) belongs to the 4d series and Hafnium (Hf) belongs to the 5d series of transition elements.
2. Usually, atomic size increases down a group. However, the filling of 4f orbitals before Hf results in "Lanthanoid Contraction" (poor shielding by f-electrons).
3. This contraction causes the atomic radius of Hf (159 pm) to be virtually identical to that of Zr (160 pm).
4. Because they have similar atomic radii and the same valence shell configuration, they possess very similar physical and chemical properties.

Concept: Transition metals have unique electronic configurations and variable oxidation states, which make them suitable for catalysis and complex formation.
Answer:
Catalytic Activity:

• Variable Oxidation States: Transition metals can easily change oxidation states, helping in redox reactions.
• Formation of Intermediates: They form unstable intermediate compounds, lowering activation energy.
• Surface Adsorption: Metals like Fe, Ni, and Pt adsorb reactants on their surface, facilitating reactions.

Formation of Complex Compounds:

• Small Size and High Charge Density: Enables strong attraction with ligands.
• Availability of d-Orbitals: Vacant d-orbitals allow coordinate bond formation.
• Variable Oxidation States: Allows formation of different complexes.

Thus, the electronic structure and chemical properties of transition metals make them effective catalysts and capable of forming numerous complex compounds.

Concept: Lanthanoid contraction refers to the gradual decrease in atomic and ionic radii of lanthanoids with increasing atomic number due to poor shielding of nuclear charge.
Answer:
Lanthanoid Contraction:
It is the steady decrease in the size of lanthanoid elements (from La to Lu) with increasing atomic number. This occurs because the added electrons enter the 4f orbitals, which have poor shielding effect. As a result, the effective nuclear charge increases, pulling electrons closer to the nucleus.
Consequences on 5d Series Elements:

• Similar Atomic Radii: The atomic radii of 5d elements become almost equal to those of corresponding 4d elements (e.g., Zr and Hf have nearly the same size).
• Difficulty in Separation: Elements with similar sizes and properties are difficult to separate.
• Higher Density: 5d elements have higher densities due to increased nuclear charge and compact size.
• Greater Stability of Complexes: Due to smaller size, 5d elements form more stable complexes.

Thus, lanthanoid contraction significantly influences the properties of 5d transition elements.