The "D and F Block Elements" is a crucial chapter in the JEE Main syllabus. It's all about those elements in the middle of the periodic table that don't fit neatly into the main groups. These elements have unique properties and play a significant role in chemistry.
In the D Block, you'll explore the transition metals like iron, copper, and zinc. They're essential in various industrial processes and are known for their colorful compounds. Meanwhile, the F Block elements, found at the bottom of the table, include the lanthanides and actinides, which have fascinating applications in nuclear reactions and technologies.
Understanding d and f block elements is essential because they can form complex compounds and exhibit a wide range of chemical behaviors. This chapter helps you grasp their electronic configurations, properties, and their significance in the real world.
Transition Elements: Characteristics, and General Trends
The transition elements, also known as transition metals, form a significant part of the periodic table. They include elements from groups 3 to 12, with the lanthanides and actinides extending the series. Transition metals are characterized by the filling of their d orbitals. These elements exhibit unique properties due to their partially filled d subshell and are found in various oxidation states. Their electronic configurations are characterized by the filling of 3d, 4d, and 5d orbitals. Understanding the transition elements and their compounds is crucial for students preparing for competitive exams like JEE Main.
Occurrence and Characteristics:
Transition elements are found in nature, often in the form of ores. They are hard, have high melting and boiling points, and possess high densities. Their unique characteristics stem from the presence of partially filled d orbitals, allowing for various oxidation states. Transition metals are excellent conductors of heat and electricity. They often exhibit magnetic properties and are widely used as catalysts in chemical reactions due to their ability to change oxidation states easily.
D - Block Elements
Groups 3 to 12 elements are called d block elements or transition elements. These elements are present between the p-block and the s-block elements in the Periodic Table. These elements' properties are intermediate between the properties of s - block and p - block elements, i.e. d - block elements represent a change or transition in properties from most electropositive s - block elements to less electropositive p - block elements. Therefore, these elements are called transition elements.
Forty elements belong to the d block. Fourth, fifth, sixth and seventh periods consist of ten elements each.
The d block elements include the most common metal used in construction and manufacturing, metals that are valued for their beauty (gold, silver and platinum), metals used in coins (nickel, copper) and metals used in modern technology (titanium). Copper, silver, gold and iron were known and used in early civilization.
Certain d block elements are particularly important in living organisms. Iron, the transition element, is present in the largest quantity in the human body. The best known biological iron containing compound is the protein haemoglobin, the red component of blood that is responsible for the transport of oxygen. Cobalt is the crucial element in vitamin Bl2, a compound that acts as a catalyst in the metabolism of carbohydrates, fats and proteins. Molybdenum and iron together with sulphur form the reactive portion of nitrogenase, a biological catalyst used by nitrogen fixing organisms to convert atmospheric nitrogen into ammonia. Copper and zinc are important in other biological catalysts. Iron, zinc, copper, cobalt, nickel, manganese and molybdenum are known to be essential components of enzymes. Vanadium and chromium are also essential for life. Some bad elements are also present in this block. For example, mercury is toxic and is a threat to the environment.
General Characteristics of D Block Elements
The members of a given transition series are not as different from each other as the members of the same period's representative elements. In a transition series, there is no change in the number of electrons of the outermost shell and only change occurs in the (n-l)d electrons from member to member in a period. These elements show horizontal and vertical relationships or they show similarities in a period as well as in group. The general trends of some of the important properties are discussed here first in the respective periods and then in groups.
1. Metallic Character
All the transition elements are metals. They exhibit most of the properties of metals. They possess high density, high melting and boiling points, ductility, high tensile strength, metallic lustre, hardness, brittleness, malleability etc. They are good conductors of heat and electricity. They exhibit all the three types of structures: face centred cubic (FCC), hexagonal closed packed (HCP) and body centred cubic (BCC). These properties reveal that both metallic and covalent bonding is present in the atoms of d block elements.
2. Atomic Radii
The transition metal atomic radii are smaller than the corresponding s - block elements. The atomic radii of the elements of a given series decrease with an increase in the number of atoms, but this reduces after midway. In the beginning, the decrease in atomic radii in each series is due to an increase in nuclear charge from member to member, which tends to pull in the ns electrons, i.e. it tends to decrease the size.
3. Ionic Radii
The ionic radii generally decrease in the same oxidation state as the atomic number increases in a given transition series.
4. Atomic Volumes and Densities
The atomic volumes of the d block elements are low as compared with elements in neighbouring s-block elements. This is because the nuclear charge is poorly screened and so it attracts all the electrons more strongly.
5. Melting and Boiling Points
The transition metals have very high melting and boiling points. The melting points of these metals rise to a maximum value in each series and then decrease as the number of atoms increases. Manganese and technetium, however, have an abnormally low fusion points.Tungsten has the highest melting point (3410°C) amongst the transition elements.
6. Ionisation Energies
Most d block elements have ionization energy values between those of s-and p-block elements. The elements of d block are less electropositive than elements of s-block and more electropositive than elements of p-block. The transition elements are not as readily forming ionic compounds as the s-block elements. The increase in the ionisation potential values in a given transition series is explained on the basis of increasing nuclear charge and screening effect of (n-l)d electrons on ns electrons. With the increase of electrons in (n-l) d subshell, the outer ns electrons are shielded more and more. Thus, the effect of significantly increasing the nuclear charge is somewhat neutralized by the extra screening effect and therefor, the potential for ionization increases but quite slowly between the d - block elements.
7. Oxidation States
The variable oxidation states of a transition metal is due to the involvement of (n-1)d and outer ns electrons in bonding as the energies of ns and (n - 1)d subshells are nearly equal. The lower oxidation state is generally shown by when ns-electrons participate in bonding and higher oxidation states are exhibited when ns and (n - 1)d electrons take part in bonding.
8. Magnetic Properties
Majority of substances show magnetic nature. These are either paramagnetic or diamagnetic. A paramagnetic substance is one which is weakly attracted in a magnetic field and a diamagnetic substance is one which is repelled by a magnetic field. The paramagnetic behaviour arises due to the presence of one or more singly occupied atomic orbitals, while diamagnetic behaviour is due to presence of paired electrons in the atomic orbitals.
Preparation, Properties, and Uses of $K_2Cr_2O_7$ and $KMnO_4$:
Potassium Dichromate ($K_2Cr_2O_7$):
Potassium dichromate, a powerful oxidizing agent, has important uses in various fields:
Preparation: Potassium dichromate is prepared by oxidizing sodium chromate with a concentrated solution of potassium dichromate or by reacting potassium chromate with sulfuric acid.
Properties: Potassium dichromate appears as bright orange-red crystals and is highly soluble in water. It is a strong oxidizing agent, meaning it readily accepts electrons in chemical reactions.
Analytical Chemistry: Potassium dichromate is used in analytical chemistry for various qualitative and quantitative analyses.
Oxidizing Agent: It is employed as a strong oxidizing agent in organic chemistry reactions.
Ink and Dye Industry: It is used in the ink and dye industry for coloration.
Photography: Potassium dichromate is used in photography as a sensitizer for gelatin emulsions.
Potassium Permanganate ($KMnO_4$):
Potassium permanganate is a versatile compound with significant applications:
$KMnO_4$ is prepared by the fusion of pyrolusite ore (MnO2) with an alkaline compound, followed by the reduction of the resulting manganate.
Properties: It is a dark purple crystalline compound and is highly soluble in water. $KMnO_4$4 is a strong oxidizing agent.
Water Treatment: Potassium permanganate is used in water treatment for the removal of iron, manganese, and hydrogen sulfide.
Organic Chemistry: It is employed as an oxidizing agent in various organic synthesis reactions.
Disinfectant: Potassium permanganate is used as a disinfectant for treating wounds and skin infections.
Analytical Chemistry: It is used in analytical chemistry as a titrant for redox titrations.
F -Block Elements
28 elements from atomic number 58 to 71 (14 elements) and from atomic number 90 to 103 (14 elements) have been arranged in two horizontal rows below the Periodic Table. These elements are collectively called the f block elements as the lastor differentiating electron in the atoms of these elements is accommodated on one of the seven f orbital of the next penultimate energy shell. These elements have also been called inner transition elements because the ante-penultimate energy shell, i.e., (n -2)f orbitals, lie comparatively deep within the kernel.
f block consists of two series of elements known as Lanthanides or Lanthanons and Actinides or Actions.The lanthanide series follows lanthanum (at. No. 57) a member of the 5d series. Similarly, actinide series comes after actinium (at. No. 89), a member of 6d series. The 14 members of lanthanide series have been placed along with lanthanum in the third group and sixth period and similarly 14 members of the actinide series have been placed with actinium in the third group and seventh period. The justification for assigning one place to these elements has been given on the basis of their similar properties. The properties are so similar that the fifteen elements from La to Lu can be considered as equivalent to one element. The same explanation can be given in the case of actinides. In case, these elements are assigned different positions in order of their increasing atomic numbers, the symmetry of the whole arrangement would be disrupted. Due to this reason, the two series of elements, i.e., lanthanides and actinides are placed at the bottom of the periodic table and constitute one block of elements, i.e. the f block. The general electronic configuration of the f block elements is:
(n-2)1-14(n-l)d0, 1ns2 or 4f1-145d0,16s2
(a) 4f Series (Lanthanides):
There are fourteen elements from cerium to lutetium in this series. The 4f orbitals are gradually filled up. In the past, these elements were called as the rare earths. This name is not appropriate because many of the elements are not particularly rare. Promethium is an artificial radioactive element.
The lanthanoids, a group of 15 elements from cerium (Ce) to lutetium (Lu), are characterized by their unique electronic configuration. They fill their 4f orbitals, leading to the general outer electron configuration [Xe] $4f^n 5s^2 5p^6$. The filling of the 4f orbitals distinguishes the lanthanoids from other elements.
Lanthanoids typically exhibit a +3 oxidation state. The outermost $5s^2$ and $5p^6$ electrons are less involved in chemical reactions, while the 4f electrons are relatively shielded by the inner electrons. As a result, the 4f electrons are not readily available for bonding, and the +3 oxidation state is the most common. However, some lanthanoids can exhibit other oxidation states, such as +2 and +4, under certain conditions.
The lanthanide contraction is a unique phenomenon observed in the lanthanide series. It refers to the steady decrease in the atomic and ionic radii of lanthanoid elements as one moves across the series from cerium to lutetium. This contraction is primarily due to poor shielding of the 4f electrons. As electrons are added to the 4f orbitals, they do not effectively shield the increasing nuclear charge, leading to a reduction in atomic size. The lanthanide contraction has important implications in the physical and chemical properties of lanthanoid elements and their compounds.
Read more about Lanthanides from Vedantu’s page.
(b) 5f Series (Actinides):
There are fourteen elements from thorium to lawrencium in this series. The 5forbitals are gradually filled up. The members of actinium are radioactive and majority of them are not found in nature. The elements from atomic number of 93 onwards are called transuranic elements and have been discovered by synthetic methods, i.e., these are man-made elements.
Actinides: Electronic Configuration and Oxidation States
The actinides, a group of 15 elements from thorium (Th) to lawrencium (Lr), fill their 5f orbitals. This results in the unique electronic configuration for actinides, with the general outer electron configuration [Rn] $5f^n 7s^2$.
Actinides exhibit a wide range of oxidation states. While the most common oxidation state is +3, actinides can display oxidation states ranging from +2 to +7 and even higher in some cases. The availability of 5f electrons for bonding allows for a diverse array of oxidation states, making actinides versatile in forming various compounds and participating in redox reactions.
Similarities of Lanthanides and Actinides
The elements of both the series show mainly +3 oxidation state.
The elements of both the series are electropositive in nature. They are reactive metals and act as strong reducing agents.
In both the series, there is a contraction in atomic and ionic size as the atomic number increases, i.e. like lanthanide contraction, them is actinide contraction. These contractions arc due to the poor shielding effect between the electrons residing in (n-2)f orbitals.
Cations with unpaired electrons in both the series are paramagnetic.
Most of the cations of lanthanides and actinides are coloured. The cations having the same number of unpaired electrons have almost the same absorption spectra. Sharp line-like bands are observed in both the series. These are due to the jump of an electron from one energy level to another within (n- 2)f orbitals.
The nitrates perchlorates and sulphates of trivalent actinides as well as lanthanides are soluble while the hydroxides, carbonates, fluorides of the elements of both the series are insoluble.
Ion exchange behaviour is exhibited by both actinides and lanthanides.
Significance of Inner Transition Elements:
Applications in Technology: Lanthanoids find applications in various technologies, including the production of phosphors for color television tubes and catalysts in petroleum refining. Actinoids, particularly uranium, play a crucial role in nuclear power generation.
Magnetic Properties: Both lanthanoids and actinoids exhibit intriguing magnetic properties. The magnetic behavior is influenced by the arrangement of electrons in the 4f and 5f orbitals, contributing to their applications in magnetic materials.
Coordination Chemistry: The f block elements are renowned for forming stable coordination compounds and complexes. The partially filled f orbitals enable them to act as Lewis acids, forming strong bonds with ligands.
Lanthanoid and Actinoid Contrasts: Understanding the contrast between lanthanoids and actinoids provides insights into the periodic trends, atomic structure, and chemical behavior of these elements, contributing to advancements in materials science and technology.
Methods Used in Metallurgy
Metallurgy is the science of extracting metals from their ores and refining them into useful materials. The different methods used in metallurgy can be broadly classified into three categories:
Pyrometallurgy: This is the most common method of metallurgy and involves the use of heat to extract metals from their ores. The ores are first crushed and concentrated, and then they are heated in a furnace with a reducing agent, such as carbon monoxide or hydrogen. The reducing agent reacts with the metal oxide in the ore to produce the metal and carbon dioxide or water vapor.
Hydrometallurgy: This method uses aqueous solutions to extract metals from their ores. The ores are first crushed and concentrated, and then they are dissolved in a solution that contains a leaching agent, such as sulfuric acid or cyanide. The leaching agent reacts with the metal oxide in the ore to produce the metal ion. The metal ion can then be recovered from the solution by precipitation or electrolysis.
Electrometallurgy: This method uses electricity to extract metals from their ores. The ore is first dissolved in an electrolyte, and then an electric current is passed through the solution. The metal ions in the solution are attracted to the cathode, where they are deposited as a metal.
Position of d and f block Elements in the Periodic Table
The d and f block elements are located in the middle of the periodic table. The d block elements are also known as the transition metals, and they are found in Groups 3 to 12 of the periodic table. The f-block elements are also known as the inner transition metals, and they are found at the bottom of the periodic table in Groups 3 and 2.
The d and f block elements are characterized by their partially filled electron orbitals. The d block elements have partially filled d orbitals, and the f block elements have partially filled f orbitals. These partially filled orbitals allow the d and f block elements to exhibit a wide range of oxidation states and to form a wide variety of compounds with different properties.
The study of D and F block elements is of paramount importance for JEE Main aspirants. These elements exhibit a wide range of unique properties, including multiple oxidation states, magnetic behavior, and complex formation. Understanding their electronic configurations and trends in atomic and ionic sizes is crucial for solving complex problems. Additionally, their applications in various industries, such as catalysis, metallurgy, and electronics, highlight their significance in the real world. Mastery of D and F block elements not only enhances performance in the JEE Main but also lays the foundation for a deeper comprehension of the periodic table and its practical applications in chemistry.