The d and f Block elements belong to the groups of 3 to 11. They are also called Transition elements and inner transition elements. Based on the 4f and 5f orbitals, the f-block elements are differentiated in lanthanides and actinides. The d block, on the other hand, is transition elements that have partially filled (n-1) d-orbitals. Transition metals found in the d and f block of the periodic table are used as catalysts. It contains elements like iron, cobalt, nickel, platinum, etc., and their compounds, which are now some of the most common catalysts used in industries.
The substances that cause a decrease in activation energy and increase the rate of a chemical reaction are called a catalyst. These substances alter the rate of a chemical reaction without themselves getting changed. However, compared to reactants, the amount of catalyst used in a chemical reaction is comparatively low. There are two types of catalysts, namely the positive catalyst and negative catalyst. The reaction rate of the reaction can be increased using a positive catalyst whereas the rate of reaction can be decreased using a negative catalyst.
The metals found in f-block and d-block are all transition metals. They form unstable intermediates with their reactants. Since they tend to exhibit variable valency, hence it results in the formation of complexes. The unstable intermediate, however, results in the production of lower activation energy for the reaction. Due to the lowering of activation energy, the rate of reaction is increased. The unstable intermediates are then decomposed to get the final product, with the catalyst being regenerated at the end of the reaction.
Catalysts provide a greater surface area for the reaction to occur; hence, it provides free valencies using which the reactant molecules are absorbed on the surface.
Catalysts are used in almost all chemical reactions. And almost all the industries have found a way to commercialize the transition metals in their industrial productions. For hydrogenation reactions to occur, a catalyst named nickel can be used. It is also mainly used in hydrogenating oil to manufacture vegetable ghee—finely divided iron acts as a catalyst for the synthesis of ammonia using Haber’s process. Also, V2O5 acts as a catalyst in the production of H2SO4 using the contact process. In the manufacturing of high-density polythene, TiCl4 is used to act as a catalyst.
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These are soft metals that have a silvery-white colour. However, when exposed to air, their colour changes become, and brightness also decreases. The melting points of the elements of 1000k to 1200k and most of them are good conductors of heat and electricity. Unlike lanthanides, actinides are pure silvery in colour. Lanthanides are non-radioactive, whereas actinides are highly radioactive elements.
Due to their radioactive nature, actinides have high reactivity, and it only increases when they are finely divided to act as a catalyst. They act as catalysts in most chemical reactions and are used only in moderations due to their high reactivity.
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The elements of d-blocks are called transitional elements and have primary usage as a catalyst for various chemical reactions. As they are present in d-blocks, their valence electrons fall under the d-orbital. They are often referred to as transitional metals, and they have electrons added to d-sub orbitals between (n+1) p and (n+1) s sub orbitals.
The elements have metallic qualities such as malleability and ductility. They even display high levels of electrical conductivity and thermal conductivity along with good tensile strength. The elements have four series that fill up the 3d, 4d, 5d, or 6d orbitals.
1. Why are Transition Metals Called “Noble Metals”?
Ans. In the transition elements, the ionization energy of the metals tends to increase slowly across rows. The density, electronegativity, electrical and thermal conductivities increase from the left of 3d series to the right corner 5d transition elements. The enthalpies of hydration in the metal cations, however, decrease in magnitude. All this leads to the transition metals becoming y less reactive and more “noble” in character. Hence they are referred to as noble metals.
Their high ionization energies and increasing electronegativity, and the decreasing enthalpies of hydration make the d block elements highly unreactive. They are thus justifying the term of Noble metals.
2. What is the Difference Between Lanthanoids and Actinoids?
Lanthanoids: They are involved in the filling of 4f- orbitals. The binding energy of 4f electrons is less than the 5f-electrons, which makes the lanthanoids less reactive. It is easy to achieve and describe the paramagnetic properties of lanthanoids. All lanthanoids are non-radioactive except promethium. They do not tend to form oxo-cations.
Actinoids: They are involved in the filling of 5f-orbitals. The binding energy of 5f-electrons is higher, but the shielding effect is less effective than the 4f-electrons. All actinide elements are highly radioactive. Actinide forms oxo-cations, and their compounds are highly basic.