Class 12 Chemistry Chapter 8 Notes
Chapter 8 of Class 12 Chemistry is about the d and f block elements.
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Our Class 12 Chemistry Chapter 8 Notes covers full chapter-related topics and sub-topics. The middle layer of the periodic table is filled with d block elements. The inner d orbits of group three to group 13 are filled progressively. On the other side, f block elements are found outside at the bottom of the periodic table. In these elements, 5f and 4f orbitals are filled progressively. Three transition elements are recognised by filling 3d, 4d, and 5d orbitals. They have a high boiling and melting point. The metallic properties of transition elements are Electrical conductivity, Malleability, Thermal conductivity, High tensile strength, Metallic character and flexibility.
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Key Topics Covered in Class 12 Chemistry Chapter 8 Notes
This chapter explains the usual or unusual properties of d and f block elements. In the periodic table, the d block consists of the elements of groups 3 to 12. The three series of the d block metals are the 3d series from Sc to Zn, 4d series from Y to Cd and 5d series from La to Hg. The fourth 6d series starts from Ac and is incomplete till now.
The following are the essential points and concepts that are covered in Class 12 Chemistry Chapter 8 Notes, related to d and f Block Elements:
- d Block Elements.
- General Properties of d-Block Elements.
- Important Alloys.
- f Block Elements.
- Lanthanide Contraction.
For every concept included in the Class 12 Chemistry Chapter 8 Notes, a brief overview of the chapter is given below.
Introduction to d-block elements
The d block of the periodic table is made up of elements from groups 3 – 12. The d orbital of the d-block elements is filled in four periods. The fourth 6d series begins with Ac and is currently unfinished.
Position in the Periodic Table:
The d and f block elements in the groups ranging from 3 to 11 are also called the transition and inner transition elements. The 4f and 5f orbitals of inner transition elements reside steadily in the latter of two extended periods. On this basis, they are differentiated into lanthanides and actinides.
Let us consider the topics that are covered in the Class 12 Chemistry Chapter 8:
Transition elements d and f Block elements:
Transition elements are found in the 3 to 12 group of the modern periodic table. Valence electrons of these transition elements fall under the d orbital. d block elements are also known as transition elements or transition metals. The first three rows of the d block elements, which correspond to the 3d, 4d, and 5d orbitals, respectively, are given below. And a more comprehensive explanation of the same can be found in our Class 12 Chemistry Chapter 8 Notes.
- Position of d Block in the periodic table: The d-block elements are found in the intermediate region of the s- and p-block elements in the periodic table. Because of its location between s- and p-block components, it was given the term ‘transition.’ The d-block elements are found in the middle section of s- and p- block elements in the periodic elements. This led to its name ‘transition’ due to its position between s- and p- block elements.
- Electronic Configuration of the d-Block Elements: The elements in the middle of the Group II-A and the Group II B elements in the present-day periodic table are the d block elements. The d-block elements may also be known as transition elements as they are elements which lie between the metals and non-metals of the periodic table.
- Generally, the electronic configuration of d-block elements is(n-1) d1–10 ns1–2. They have two incomplete outer shells. where (n–1) = Inner d orbitals show electrons from 1-10, ns = Outermost orbital may have one or two electrons. (n-1) d10 n s2 shows the electronic configurations of Zn, Cd and Hg. They exhibit variable valency that differs by units of one.
There are four transition series in the d block, corresponding to the filling up of 3d, 4d, 5d or 6d orbitals.
- i) 3d- Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn.
- ii) 4d- Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd.
iii)5d- La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg.
- iv) 6d- Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn
Ten elements are filling up the ‘d’ orbital in each series.
All transition elements show similar properties because of the identical electron configuration of their peripheral shell. This happens as each additional electron enters the penultimate 3d shell. This creates an effective shield between the nucleus and the 4s outer shell. The peripheral shell configuration of these transition elements is ns2.
The physical properties of the transition elements as discussed in our Class 12 Chemistry Chapter 8 Notes are as follows:
- Form stable complexes.
- Having high melting and boiling points.
- Consist large charge/radius ratio.
- Form compounds which are often paramagnetic.
- They are complex and possess high densities.
- Form compounds with profound catalytic activity.
- Show variable oxidation states.
- Form coloured ions and compounds.
As fewer electrons are in the peripheral shell, all the transition elements become metals. Metals exhibit ductility and malleability qualities, and they are good conductors of electricity and heat. Apart from Hg, which is fluid and delicate like alkali metals, all the transition elements are rigid and fragile.
Melting and Boiling points:
They exhibit high melting points and boiling points. This is due to the overlapping of (n-1)d orbitals and the covalent bonding of the unpaired d orbital electrons. Zn, Cd, and Hg have filled (n-1)d orbitals. They cannot form covalent bonds. Hence, they have a lower melting point than other d-block elements.
The transition elements are highly denser than the s block elements. Their densities gradually decrease from scandium to copper because of an irregular decrease in metallic radii and a relative increase in atomic mass. The pattern of the ionic radius is the same as that of the atomic radii pattern. Thus, for ions of a given charge, the ionic radius gradually decreases with an increment in atomic number.
As explained in our Class 12 Chemistry Chapter 8 Notes, the ionisation potential of transition elements lies between s and p block elements. They are significantly less electropositive than the s-block elements. Hence, they do not frame ionic compounds but form covalent compounds. They possess high ionisation energy because of their small size.
The ionisation potential of d-block elements increases from left to right. The ionisation energies of the primary transition elements increase with the increase in the nuclear number.
For example, Cr and Cu have higher energies than their neighbours.
The external electronic configuration is consistent. There is a gradual filling of 3d orbitals across the series starting from scandium.
However, this filing is not regular since, at chromium and copper, the population of 3d orbitals increases by acquiring an electron from the 4s shell. At Cr, both the 3d and 4s orbitals are occupied, but neither of the orbitals is filled. This indicates that the energies of the 3d and 4s orbitals are relatively close for atoms in this row.
The electronic configurations of the first, second, and third series elements are:
- First series: 1s22s2p63s2p6d1–104s2
- Second series: 1s22s2p63s2p6d1-104s2p6d1-105s2
- Third series: 1s22s2p63s2p6d1-104s2p6d1-10 5s2p6d1-106s2
These three series of elements depend on the n-1 d orbital being filled. The details of the electronic configuration of the first, second, and third series elements are covered at length in our Class 12 Chemistry Chapter 8 Notes. An orbital of lower energy is occupied first. Thus, 4s orbital with lesser energy is filled first to its full degree. After 4s, the 3d orbital with higher energy is filled. The precisely half-filled and filled d-orbitals are exceptionally stable.
Apart from the first and the last, all the transition elements display various oxidation states. At first, there is an increase in the number of normal oxidation states to a maximum toward the middle of the table and when we move from left to right across the first transition series.
The elements Sc through Mn (the first half of the first transition series) show the highest oxidation state as their valence shell represents a loss of all electrons in both the s and d orbitals. Iron shows oxidation states from 2+ to 6+ states. Elements in the first transition series show ions with a charge of 2+ or 3+ states. The elements belonging to the second and third transition series generally are more stable in higher oxidation states than the elements of the first series.
Magnetic Properties of d Block Elements:
Materials are differentiated by their interaction with the magnetic field as:
- Diamagnetic: If repelled.
- Paramagnetic: If attracted.
- Ferromagnetic: If it can retain the solid magnetic nature even without a magnetic field.
- Paired electrons cause diamagnetism.
- Unpaired electrons show in paramagnetism and are aligned together.
- Unpaired electrons form ferromagnetism. d block elements and their ions show this magnetic behaviour based on the unpaired electrons.
As unpaired electrons are involved in ‘Orbital Magnetic Moment’ and ‘Spin Magnetic Moment’. Thus, for the 3d series, the orbital angular moment is negligible, and the formula gives the approximate spin-only magnetic moment:
µ = √[4s (s + 1)] = √[n (n + 1)] BM
Here ‘s’ is the total spin and ‘n’ is the number of unpaired electrons.
Its unit is known as “Bohr Magneton (BM)”.
For higher d-series, the actual magnetic moment includes components from the orbital moment and the spin moment. Chromium and molybdenum possess the highest number (6) of unpaired electrons and magnetic moment.
Many students find the topic of magnetic properties of d Block elements a bit challenging. We recommend students to refer to our Class 12 Chemistry Chapter 8 Notes to get an easy-to-understand format of this topic to get the hang of it. These notes strictly follow the NCERT books and provide solved exercises and practice questions to clarify your doubts and supplement your learning and boost your performance.
Formation of Coloured Ions by Transition Elements:
Compounds of d block elements have different colours. If a frequency of light is absorbed, the light transmitted exhibits a colour complementary to the frequency absorbed. d block element ions can absorb the frequency in the visible region and use it in two ways to produce visible colour.
Cupric ions are colourless, and in the presence of water, molecules become blue:
- a) Colour of the ions differs with their oxidation state. The Cr6+, as in potassium dichromate, is yellow, whereas Cr3+ and Cr2+ are generally green and blue colours, respectively.
- b) Colour of the compound is based on the coordinating group.
For example, Cu2+ shows a light blue colour in the presence of water as a ligand but a deep blue colour in ammonia as the ligand.
- c) Transition metal ions which have:
- Completely occupied d-orbitals with no vacant d-orbitals for excitation of electrons are colourless. Ion Cu+(3d10), Zn2+(3d10), Cd2+(4d10) Hg2+(5d10), and Zinc, Cd, Hg are colourless.
- Transition metal ions which have empty d-orbitals without d-electrons are also colourless. Sc3++(3d0), and Ti4++(3d0), ions are colourless.
L-M and M-L dπ – pπ bonding:
Ligands can donate their p electrons into the empty d orbitals of metal ions. This interaction, known as ligand-metal/metal-ligand or dπ – pπ bonding, may also colour the compounds.
Complex Formation Tendency of d Block Elements:
Complex compounds are compounds wherein several neutral molecules or anions are combined with metal. Metals part of the d block elements form many complex compounds due to their small ionic size, high charge, and relative availability of d orbitals to form bonds.
Transition metal and their ions, with more significant nuclear charge and smaller size, can attract electrons and receive lone pairs of electrons from anions and neutral molecules into their vacant d-orbitals, forming coordinate bonding.
Transition elements form complex molecules with CO, NO, NH3, H2O, F–, Cl–, and CN–.
Example of transition metal complexes are, [Co(NH3) 6] 3+ [Cu(NH3)4] 2+, Y(H2O) 6]2+, [Fe(CN)6]4−, [FeF6] 3−, [Ni(CO)4].
The topic of complex formation tendency of d-Block elements is made easy by Extramarks experienced faculty by using simple language, with detailed explanations of each and every topic in their Class 12 Chemistry Chapter 8 Notes. Extramarks has a repository of resources for students to help them with tricky and complex topics besides providing revision notes which come in handy during tests and exams.
Catalytic Activity of Elements:
Catalysts are essential for the industrial bulk production of many chemicals. Several d-block elements, as metals are in their ionic form, are being used as a catalyst in many chemical and biological reactions.
In Haber’s method, iron to make ammonia, vanadium pentoxide used in sulphuric acid production, and titanium chloride used as Zigler Natta catalyst in polymerisation are essential commercial catalytic methods involving d block metals.
Most transition elements behave as good catalysts because:
- The presence of vacant d-orbitals.
- The tendency to show variable oxidation states and form reaction intermediates with reactants.
- The +nce of defects in their crystal lattices.
They take the chemical reaction through a path of low activation energy in the following ways:
- Given a large surface area for absorption and sufficient time to react.
- They may interact with the reactants through their vacant orbitals.
- Redox reactions may actively combine it through their multiple oxidation states.
Alloy Formation in transition elements:
Atomic radii of the d block elements in any series are not much different. As a result, they can easily replace each other in the lattice and form solid solutions over an appreciable composition range. Atoms within 15% of the difference in radii may form alloys. Such solid solutions are known as alloys.
- Alloys are homogeneous solid solutions of 2 metals or metals with a non-metal. The alloys of transition metals are complex.
- Various steels are iron alloys with metals such as chromium, vanadium, molybdenum, tungsten, manganese etc.
Refer to Extramarks Class 12 Chemistry Chapter 8 Notes where our Chemistry subject matter experts have explained Alloy formation in further detail.
Few important alloys:
- Bronze : Cu(75-90%) + Sn (10-25%).
- Chromium steel :Cr(2-4% of Fe).
- Stainless steel: Cr(12-14% and Ni(2-4%) of Fe,
- Solder: Pb +Sn.
Along with our Class 12 Chemistry Chapter 8 Notes, students can refer to a repository of resources which includes -NCERT Solutions, CBSE Revision Notes, etc. for Class 12 Chemistry to supplement their learning with detailed explanation about this chapter. These notes are proven to be helpful, and it makes it easier for students to revise the whole chapter quickly.
Interstitial Compounds of d Block Elements:
Transition metal has a gap in its crystal lattice structure. Tiny non-metallic atoms and molecules like hydrogen, boron, carbon etc., can be trapped in the void during crystal structure formation. These are called interstitial compounds. They are neither ionic nor covalent nor non-stoichiometric, as in TiH1.7 and VH0.56.
Examples of the interstitial compounds formed with transition metals are
Formation of Complex Compounds:
The cations of transition metals tend to form complex compounds with several molecules or ions known as ligands. The bonds that participate in the formation of complexes are coordinated, and hence the complexes represent coordinated complexes. The structure of various ions is linear, square, planar, tetrahedral, and octahedral, depending upon the nature of the hybridisation of metal ions.
The weak ligands like CO and NO form complexes only if transition metals are at zero due to the availability of vacant orbitals in the donor atom of the ligand in addition to the lone pair. The highly electronegative and primary ligands like F–and Cl– can form complexes with transition metals.
In a transition metal series, the stability of complexes is enhanced with the increase in atomic number. The transition metal atom reveals multiple oxidation states, and the higher valent ion forms more stable complexes.
Additional explanation of the process has been provided with illustration and key notes in Extramarks Class 12 Chemistry Chapter 8 Notes.
Here are some examples of complex compounds:
- i) [Fe (CN)6]3–
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Introduction to f-block elements
The elements with gradually occupied f orbitals are called f-block elements. The elements of the 4f series of the inner transition metals are called lanthanides, whereas the elements of the 5f series are called actinides.
f block elements are categorised into two series, namely lanthanoids and actinoids. This block of elements is often referred to as inner transition metals. They give a transition in the 6th and 7th row of the periodic table, separating the s block and the d block elements. Extramarks team of Chemistry experts have explained this process in simple and easy language in our Class 12 Chemistry Chapter 8 Notes so that students may continue their studies uninterrupted as well as save time for other subjects too
The inner transition elements:
They are the 4f series of Ce to Lu and the 5f series of Th to Lw. 14 elements fill up each series ‘f’ orbital.
The elements showing up in the f block are further classified into:
- The first series of elements are known as lanthanides and include elements with atomic numbers starting from 57 and ending at 71. These elements are non-radioactive (except for Promethium, which is radioactive).
- The second series of elements are actinides and include elements with atomic numbers starting from 89 and ending at 103. These elements generally show radioactive behaviour.
The list of all the inner transition elements is shown below. The row starting with lanthanum is the row containing all the lanthanides, whereas the row starting with actinium is the row that contains all the actinides.
Properties off Block Elements:
- Electrons are filled to the ‘f’ sub-orbitals of the (n-2) level.
- They are placed between (n-1)d and ns block elements in the periodic table.
Properties of Lanthanides:
Lanthanides are soft metals with a silvery-white colour. Their colour dulls, and their brightness decreases rapidly when exposed to air.
- Lanthanides series melting points range from 1000K to 1200K (Except Samarium, 1623K).
- Ln are good conductors of heat and electricity.
- Ln are non-radioactive except for Promethium.
- A decrease in atomic and ionic radii from lanthanum to lutetium is observed. This is called the lanthanoid contraction.
Properties of Actinides:
The Actinide elements appear silverish. These elements show radioactive behaviour. These inner transition metals are highly reactive, and their reactivity enhances if they are finely divided. A decrease in atomic radii and ionic radii from Actinium to Lawrencium is observed. It is known as the actinoid contraction. They generally show an oxidation state of +3. However, elements belonging to the first half of the series are frequently known to exhibit higher oxidation states.
Class 12 Chemistry Chapter 8 Notes covers the topic of Lanthanides and Actinides with visual diagrams and notes that will make it easier for students to understand the complex properties of both Lanthanides and Actinides
Oxidation state in Actinoids:
Generally, the oxidation state of these elements is +3 (same as lanthanides). They also exhibit +4 oxidation states. Some of the elements also indicate higher oxidation states. The oxidation state initially increases to the middle of the series (+4 for Th to +5, +6 and +7 for Pa, V and Np) and then descends in the succeeding elements.
General Characteristics & Comparison of Actinoids with Lanthanoids
(a) Electronic configuration: The general electronic configuration for actinoids is [Rn]86 5f1-14 6d0-1 7s2 and for lanthanoids is [Xe]54 4f0-14 5d0-1 6s2.
(b) Atomic and ionic sizes: Like lanthanoids, the ionic radii of actinoids gradually decrease across the series due to the poor screening effect of nuclear charge exerted by the f electrons.
(c) Oxidation states: The lanthanides exhibit +3 oxidation states. Some elements may show + 2 and + 4 oxidation states due to extra stability of fully-filled and half-filled orbitals. On the other hand, Actinoids also exhibit a + 3 oxidation state. They also show varying oxidation states due to the comparable energies of 5f, 6d, and 7s.
(d) Chemical reactivity: Earlier members of the lanthanide series are more reactive and are comparable to the solution. They resemble Al with increasing atomic numbers. Finely divided Ac are highly reactive metals and, when added to boiling water, give a mixture of oxide and hydride. At moderate temperatures, actinoids were added with most of the non-metallic elements. Ac remains unaffected by the action of alkalies but gets slightly affected by nitric acid due to the formation of a protective oxide layer.
Applications of d- and f-Block Elements as covered in our Class 12 Chemistry Chapter 8 Notes:
- Iron and steel are used for making tools, utensils, vehicles, bridges and much more.
- TiO for the pigment industry and MnO2 for use in dry battery cells.
- Zn and Ni/Cd are also used in the battery industry.
- Elements of Group 11 are called the coinage metals.
- V2O5 catalyses the oxidation of SO2 in the manufacture of sulphuric acid.
- In the Haber process, iron catalysts produce ammonia from N2/H2 mixtures.
- Nickel catalysts enable the hydrogenation of fats.
- In the Wacker process, ethyne’s oxidation to ethanal is catalysed by PdCl2.
- Nickel is helpful in the polymerisation of alkynes and other organic compounds such as benzene.
- The photographic industry relies on the unique light-sensitive properties of AgBr.
For example:. Write down the electronic configuration of Cr3+ ion
Cr3+:- 1s2 2s2 2p6 3s2 3p6 3d3
For further step-by-step understanding of the applications of d- and f-block elements, students can refer to Class 12 Chemistry Chapter 8 Notes to nail the tests, exams and stay ahead of the competition.
Class 12 Chemistry Chapter 8: Exercise & Solutions
The Class 12 Chemistry Chapter 8 Notes exercise and solutions are based on NCERT books. Every exercise is compiled to add more value to the chapter. Students may refer to various study materials such as revision notes, past year questions papers, essential questions, and more about NCERT solutions on the Extramarks website.
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Key Features of Class 12 Chemistry Chapter 8 Notes
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