Characteristics of Catalytic Behaviour in D and F Block

Transition metals and their compounds work as catalysts owing to its ability to change oxidation state or, in the case of the metals, their adsorption capability and activate other molecules on their surface. Transition metals exhibit catalytic behaviour for a variety of reasons: The presence of d orbitals that are empty. They have the ability to display a wide range of valencies. They have a tendency for forming complicated chemicals.

Characteristics of D and F Block

The attributes of d-block elements are listed below:

• These are metallic in nature, with great density and hardness.
• They have high melting and boiling points, as well as a variety of oxidation states.
• They generate a wide range of coloured ions and molecules.
• As the atomic number rises, the atomic radii decrease.

The general properties of f-Block Elements are listed below:

• They are paramagnetic in nature, with a higher proportion of radioactive elements than the other blocks.
• They exhibit a range of oxidation states.
• They have a protecting effect on them. Shielding occurs when an electron’s attraction to an atom decreases as it moves away from the nucleus. This is due to the weakening of the forces that hold atoms together as distance rises.

Catalytic properties of d and f block

Transition metals have catalytic properties for the following reasons:

Variable oxidation state

Transition metals generate unstable intermediate compounds with variable oxidation state. These intermediate molecules give a novel path for the reaction with a lower activation energy (Intermediate Compound Formation Theory).

Large Surface Area

Finely split transition metals or their compounds provide the large surface area for adsorption, and the adsorbed reactants react faster as a result of the tighter contact.

Transition metals & their compounds are significant and effective catalysts in both industrial & biological applications. Transition metals are good catalysts because of their availability of 3d & 4s e- and their ability to shift oxidation states. A Solid Transition Metal Catalyst with reactants in gas or liquid phases is said to be in a distinct phase than the reactants. Transition metals can create weak bonds to reactants by using electrons from the 3d & 4s orbitals on complex ion (ligand) surface. These connections can be broken to release products once the reaction has happened on a metallic surface.

General characteristics of d-block elements

 Atomic and Ionic Radii

Transition elements have smaller atomic and ionic radii than p-block elements and greater atomic and ionic radii than s-block elements. The first transition series’ atomic radii decline from Sc to Cr, remain about constant until Cu, and then increase at the end. Screening and the nuclear charge effect are two effects that help explain this. These two effects cancel each other out, resulting in a nuclear charge rise. As a result, there is only a very tiny difference in the atomic radii from Cr to Cu.

It has been discovered that the atomic radii of zirconium and hafnium are nearly comparable. Because of lanthanide contraction, this is the case.

Metallic character

Because the number of electrons in the outermost shell is very minimal, equal to two all transition elements are metals. They are rigid, bendable, and capable of forming coloured ions.

In their solid or solution forms, most transition metal complexes are coloured. The existence of unpaired electrons and a small energy gap between two energy levels in the same d-subshell give transition metal ions their colour. As a result, only a minimal amount of energy is needed to excite electrons from one energy level to the next. The visible light can simply offer energy. The colour seen matches to the light absorbed complementary colour.

Catalytic Properties of d block elements

As catalysts, the majority of transition metals and their derivatives are utilised.

• Transition metals’ catalytic activity is attributed to the following factors.
• They have a wide range of oxidation states and can thus create intermediate products with a variety of reactants.
•  They can also produce interstitial compounds that adsorb and activate the reactive species.
• Here are some examples of catalysts:
•  In Haber’s Process, iron and molybdenum act as catalysts in the creation of ammonia.
• For catalytic oxidation ofSO2 to S03, vanadium pentoxide (V2O5) is utilised.
• Ticl4 is used.

Variable oxidation states

In their compounds, all transition elements have a variety of oxidation states(or)variable valencies. Because of the following factors, this trait exists.

• These elements have (n-1) electrons in the d and ns orbitals.
• The energies of the (n-1)d and ns orbitals are relatively close.

General Characteristics of f-block elements

The Lanthanide Series

The Lanthanide series consists of fifteen elements, ranging from lanthanum (57 La) through lutetium (58Lu) to (71Lu). Lanthanum and lutetium have electrons in the 5d-subshell but no partially full 4f-subshell. As a result, these aspects should be excluded from this series. All of these elements, however, have a strong resemblance to lanthanum and are so grouped together.

Cause of lanthanide contraction

The poor shielding of one 4f electron by more in the same sub shell causes the lanthanide contraction. Each step along the lanthanide series increases the nuclear charge and the amount of 4f electrons by one unit. However, because to insufficient shielding, the effective nuclear charge rises, forcing the electron cloud of the 4f-subshell to compress.

Actinides

The distinguishing electron in actinides enters 5f orbitals. These are the ratios of thorium to lawrencium. 

Conclusion

Transition metals are elements in the periodic table’s d-block that have partially filled d orbitals. The reactivity of transition metals ranges from highly active metals like scandium and iron to nearly inert elements like platinum metals. The type of chemistry utilised to separate elements from their ores is determined by the element’s concentration in its ore as well as the difficulty of reducing ions to metals. Metals with a higher level of activity are more difficult to remove. Transition metals have metal-like chemical properties. They oxidise in air and react with elemental halogens to create halides, for example. The elements in the activity series above hydrogen react with acids to produce salts and hydrogen gas. Transition metal compounds’ oxidides, hydroxides, and carbonates in low oxidation states are basic.