The d and f Block Elements (d -Block Elements)

The d and f Block Elements d -Block Elements o 1st Series - They are classified in fourth period and are called as ‘3d’ series of elements. Their atomic numbers are 21(Sc) to 30 (Zn). In the long form of periodic table elements are classified based on electronic configuration. The elements which are classified between’s’ and ‘p’ block are ‘d’ block elements or Transition elements. In these elements the differentiating electron enters in the ‘d’ orbitals of penultimate shell. General configuration for ‘d’ block elements is ns1-2 (n-1)d1-10. i.e., in ‘d’ block elements the valence shell has constant number of electrons whereas the number of electrone in penultimate shell go on increasing. Elements which have atleast one unpaired electron o in their ‘d’ orbital in atomic or any oxidation state are called as Transition elements. Thus all transition elements are ‘d’ block elements but all ‘d’ block elements may not be transition elements or the elements having incompletely filled ‘d’ orbitals are called as transition elements. Transition elements are classified between’s’ and ‘p’ blocks from fourth period onwards. Series of transition elements are four 2nd Series- They are classified in fifth period and are called as ‘4d’ series of elements. Their atomic numbers are 39(Y) to 48(Cd). TRANSITION ELEMENTS AND COMPLEXES o o o o 3rd series- They are classified in sixth period and are called as ‘5d’ series of elements. Their atomic numbers are 57(La), 72(Hf) to 80(Hg) 4th Series - They are classified in the seventh period and are called as ‘6d’ series of elements. This is an incomplete series. Their atomic numbers are 89(Ac), 104(Ku) to 112 (Uub). Electronic configuration of first series of transition elements. Atomic number 21. 22. 23. 24. 25. 26. Element Symbol Scandium Sc Titanium Ti Vanadium V Chromium Cr Manganese Mn Iron Fe Electronic configuration [Ar) 4s23d1 [Ar] 4s23d2 [Ar) 4s23d3 [Ar) 4s13d5 [Ar] 4s23d5 [Ar) 4s23d6 75 The d and f Block Elements [Ar) 4s23d7 o o 27. Cobalt Co 28. Nickel Ni [Ar) 4s23d8 29. Copper Cu [Ar) 4s13d10 30. Zinc Zn [Ar] 4s23d10 Chromium and copper are elements having exceptional electronic configurations of [Ar] 4s13d5 and [Ar] 4s13d10 instead of [Ar] 4s23d4 and [Ar] 4s23d9 Zn (30) is [Ar] 4s23d10 Cd (48) is [Kr] 5s24d10 Hg (80) is [Xe] 6s2 4f14 5d10 These three elements do not have any unpaired electrons in their ‘d’ orbitals in atomic as well as in ionic states.Therefore they are only classified as ‘d’ block elements and not as transition elements. Copper, Silver and Gold, the elements of IB group i.e., coinage metals, have ns1 (n-1)d10 configuration. They are transition elements as in their higher oxidation state they have an unpaired electron in their ‘d’ orbitals. GENERAL PROPERTIES OF D-BLOCK ELEMENTS o o o 1. o o o All the elements of ‘3d’ series are good reducing agents except copper. In general the reactivity of transition elements is less. Their reactivity decreases with increase in atomic number. The atomic radii of trarsition elements decrease by negligible amounts due to the shielding of valence shell electrons, provided by electrons of ‘d’ orbitals of penultimate shell. The ionisation potential of transition elements increase by negligible amounts due to shielding effect. Metallic Character All the d-block elements are metals as the numbers of electrons in the outer most shell are one or two. They are hard malleable and ductile. IB group elements Cu, Ag and Au are most ductile and soft. These are good conducter of heat and electricity (due to free e-) IB gp. elements are most conductive in nature. Their order of conductivity is Ag > Cu > Au > AI. 2. o o o o o o o 3. o o o o o o o Atomic size Atomic and ionic radii of d-block elements is smaller than s-block elements Atomic radii depends on effective nuclear charge (Zeff) and screening effect (SE). In 3d reries Sc  Cr (Zeff > SE)  radius decreases Mn  Ni (Zeff = SE)  radius remains constant Cu  Zn (Zeff < SE)  radius increases In dipositive ions of 3d series Cu+2 is the smallest in size. The elements of 4d and 5d series belongs to a particular group have almost same atomic radii. This is due to Lanthanide contraction. e.g. Zr Hf, Tcc Re, Nb Ta, Ru Os etc. In d-block elements Largest atomic radii - La Smallest atomic radii - Ni In IllB group order of atomic radii is Sc < Y < La (No lanthanide contraction) Density The atomic volume of the transition elements are low compared with s-block, so their density is comparatiely high (D = M/V) Except Sc, Y and Ti, all the d-block elements have density greater than 5gm cm–3 Os (22.57 gm cm–3) and Ir (22.61 gm cm–3) have highest density. In all the groups there is normal increase in density from 3d to 4d series, and from 4d to 5d it increases just double it is due to lanthanide contraction. Ti < Zr << Hf In 3d series Sc  Cr density increases Mn, Fe, Co, Ni  almost constant Cu  Zn decreases In 3d series highest density – Cu lowest density – Sc Some important orders of density Fe < Ni < Cu Fe < Cu < Au Fe < Hg < Au 76 4. Melting and boiling points o M.P. and b. p. of d-block > s-block (the reason is stronger metallic bond and presence of covalent bond formed by unpaired d-electrons.) o o o (a) Variable oxidation state (b) Coloured ions In Zn, Cd, and Hg there is no unpaired electron present in d-orbital, hence due to absence of covalent bond, their m.p. and b.p. are very low. (Volatile metals Zn, Cd, Hg) (c) Paramagnetic properties (d) Catalytic properties (e) Formation of alloys In 3d series (f) Formation of interstitial compounds and Sc  Cr m.p. b.p increases o o Mn  Zn m.p. b.p decreases Mn and Tc possess comparatively low m.p., it due to stable configuration’ (Half filled) Lowest mp Hg - 38°C (g) Formation of complexes. (a) Variable valency or variable oxidation states: They exhibit variable valeney due to involvement of (ns) and (n-1)d electrons in bonding. This is due to less energy difference between these electrons. Highest mp. W  3400°C o o o The d and f Block Elements Characteristic properties of transition elements are The oxidation states of all transiition elements of ‘3d’ series are as follows Sc [Ar] 4s23d1 Ti [Ar] 4s23d2 (+2) +3 +4 V [Ar] 4s23d3 +2 +3 +4 +5 Cr [Ar] 4s13d5 (+1) +2 +3 (+4) (+5) +6 Mn [Ar] 4s23d5 +2 +3 +4 (+5) (+6) +7 Fe [Ar] 4s23d6 +2 +3 (+4) (+5) (+6) Co [Ar] 4s23d7 +2 +3 +4 Ni [Ar] 4s23d8 +2 (+3) (+4) Cu [Ar] 4s13d10 +1 +2 +3 Highest oxidation state of transition elements can be o calculated by = n + 2 (n = no. of unpaired e-) (It is not applied for Cr and Cu) The transition metal ions having stable configuration o are stable Metal ions of ‘3d’ series having 3dº configuration o Sc+3, Ti+4 and V+5 etc are stable. Transition metal ions having 3d5 configuration are stable like Mn+2, Fe+3 In aqueous medium Cr+3 is stable. Co+2 and Ni+2 are stable. o Transition metal ion with 3d10 configuration which is stable is Cu+1. In aqueous medium Cu+2 is more stable than Cu+1. Most common oxidation state among the transition elements is +2. Highest oxidation state shown by transition elements of ‘4d’ and ‘5d’ series is +8. The elements showing this oxidation state are Ruthenium (44) and Osmium (76). The common oxidation state shown by elements of IIIB i.e., Sc, Y, La and Ac is +3 as their divalent compounds are highly unstable. 77 The d and f Block Elements o o In lower oxidation state transition elements form ionic compounds and in higher oxidation state their compounds are covalent. Ti+2[Ar]3d2, V+2[Ar]3d3 etc. e.g. in chromate ion CrO4–2, the bonds between Cr o and O are covalent. Transition metal ions which do not have any unpaired elctrons in their ‘d’ orbitals like 3d 0 and 3d10 configurations, do not exhibit any colour property. These are having unpaired electrons in their ‘d’ orbitals therefore they are coloured. Generally higher oxidation states are exhibited in the compounds which are formed with highly electronegative elements like O and F. e.g., Sc+3 [Ar]3d0, Cu+1[Ar]3d10, Ti+4[Ar]3d0 etc are colourless ions. o They also shows zero oxidation state in their carbonyl o compounds like Ni(CO)4 o Usually transition metal ions in their lower oxidation state act as reducing agents and in higher oxidation state they are oxidising agents. e.g. – Ti+2, V+2, Fe+2, Co+2 etc are reducing agents o Cr+6, Mn+7, Mn+4 Mn+5, Mn+6 etc are oxidising agents. 5. Colour Property: o Most of the transition metal ions exhibit colour property. This is due to the presence of unpaired electrons in their ‘d’ orbitals. They require less amount of energy to undergo excitation of electrons. Hence they absorb visible region of light exhibiting colour. o KMnO4 (dark pink), K2Cr2O7 (orange) having dº onfiguration are coloured due to charge transfer spectrum. Some of the coloured metal ions are as follows: Ti+3 - Purple Cr+3 Green Mn+2 - Light pink Fe+2 - Pale green Fe+3 - yellow Co+2 - Blue Ni+2 green Cu+2 - Blue A transition metal ion absorbs a part of visible region of light and emits rest of the six colours, the combination of which is the colour of emitted light. The colour of metal ion is the colour of the emitted light. In transition metal ion the ‘d’ orbitals split into lower energy set t2g orbitals and higher energy set eg orbitals. The electrons from t2g set get excited to higher energy set i.e., eg set. This excitation of electrons is called as ‘d-d’ transition. As d-d transition requires less amount of energy they absorb visible region of light. Due to this ‘d -d’ transition the transition metal ions exhibit colour property. Lower energy set = t2g Higher energy set = eg. 6. Magnetic properties o Matter, in general is associated with magnetic properties. Majority of substances are either paramagnetic or diamagnetic. A paramagnetic substance is one which is attracted into a magnetic field. Paramagnetism is mainly due to the presence of unpaired electrons in atoms or ions or molecules. Diamagnetic substance is one which is slightly repelled by a magnetic field. 78 o Ti +2 [Ar]3d 2 , Ti +3 [Ar]3d 1 . V +2 [Ar]3d 3 , o Cr+3[Ar]3d3 o o o As is evident most of the transition metal ions have (i) Fe is used in Haber’s process for manufacture. of unpaired electrons in their ‘d’ orbitals. Hence most NH3. of the transition metal ions are paramagnetic in nature. Transition metal ions having 3d 0 and 3d 10 (ii) V2O5 is used in contact process for H 2SO 4 manufacture configuration exhibit diamagnetic nature. An unpaired electron spins and as it is a charged (iii) Pt is used in Ostwald’s process of nitric acid particle, magnetic field is created due to its spinning. (iv) Ni is used in hydrogenation of oils Each electron may, in fact, be considered as a micro magnet having a certain value of magnetic moment. The total magnetic moment of a substance is the resultant of the magnetic moments of all the individual electrons. Thus substances containing unpaired electrons get attracted towards the magnets exhibiting paramagnetic nature. (v) FeSO4 is used in oxidation of Benzene with H2O2 (vi) Cu is used in dehydrogenation of alcohols (vii) TiCI4 is used as catalyst in Vinyl polymerisation. 8. Formation of Alloy o Transition elements have maximum tendency to form alloys. The magnetic moment () created due to spinning of o unpaired electrons can be calculated by using = n(n  2) : Where ‘n’ is the number of unpaired electrons in the metal ion.  = Magnetic moment in Bohr Magnetons (B.M.) o o 7. o o o The reactivity of transition elements is very less and their sizes are almost similar. Due to this a transition metal atom in the Lattice can be easily replaced by other transition metal atom and hence they have maximum tendency to form alloys. In the alloys ratio of component metals is fixed. The magnetic moment of diamagnetic substances will o These are extremly hard and have high M.P. be zero. As the number of unpaired electrons increase the SOME IMPORTANT ALLOY magnetic moment created goes on increasing and hence the paramagnetic nature also increases. o The d and f Block Elements Transition metals and their compounds exhibiting catalytic properties in various processes are 1. Bronze - Cu (75 - 90 %) +Sn ( 10 - 25 %) Transition metal ions having d5 configuration will have maximum number of unpaired electrons therefore 2. they will be maximum paramagnetic in nature. Brass - Cu ( 60 - 80 %) +Zn (20 - 40 %) Catalytic Property 3. Transition elements and their compounds exhibit catalytic properties. This is due to their variable valency as well as due to the free valencies on their 4. surface. 5. Gun metal - (Cu + Zn + Sn) When transition elements and their compounds are 6. in powdered state. their catalytic properties exhibited 7. will be to a greater extent. This is due to greater 8. surface area available in the powdered state. (87 : 3 : 10) German Silver - Cu + Zn + Ni ( 2 : 1 : 1) Bell metal - Cu (80%) + Sn (20%) Nichrome - (Ni + Cr + Fe) Alnico - (Al, Ni, Co) Type Metal - Pb + Sn + Sb 79 9. Alloys of steel (a) Vanadium steel (b) Chromium steet (c) Nickel steet (d) Manganese steel (e) Stainless steel - V (0.2 – 1%) Cr (2 – 4%) Ni (3 – 5%) Mn (10 – 18%) Cr (12 – 14%) & Ni (2–4%) W (10 – 20%) Ni (36%) 54% Au + Ag (14 to 30%) + Cu (12 – 28%) 100% Au Pb + Sn Mg (10%) + Al (90%) (Al + Mn + Cu) Cu (90%) + Al (10%) Cu (60%) + Ni (40%) The d and f Block Elements POTASSIUM PERMANGANATE (KMnO4) o Potassium Permanganate (KMnO4) is an inorganic chemical compound. It is also known as Condy's crystals or permanganate of potash. o A German-Dutch chemist Johann Rudolf Glauber was the first to discover the production of KMnO4 in the year 1659. This compound is water-soluble and consists of two ions: Permanganate ion and potassium ion. It is a dark purple odourless solid in its physical state. o When potassium permanganate crystals are dissolved in water the solution formed is purple in colour. It is considered as a strong oxidizing agent and does not produce toxic byproducts. It is usually prepared from other minerals such as manganese oxide Potassium Permanganate Structure - KMnO4 (f) Tunguston steel (g) Invar 10. 14 Carat Gold - 11. 12. 13. 14. 15. 16. 24 Carat Gold Solder Magnallium Duralumin Artificial Gold Constantan - 1. % of Carbon in different type of Iron: Name % of C (i) Wrought Iron .1 to .25 Preparation Of Potassium Permanganate - KMnO4 (ii) Steel .25 to 2.0 o Potassium permanganate is commercially prepared (iii) Cast Iron 2.6 to 4.3 by mixing solution of KOH and powdered (iv) Pig Iron 2.3 to 4.6 manganese oxide, with oxidizing agents like potassium Formation of Interstitial Compounds chlorate. The mixture is boiled evaporated and the Transition elements form interstitial compounds with residue is heated in iron pans until it has acquired a smaller sized non metal elements like hydrogen, pasty consistency. carbon, boron, nitrogen etc. The smaller sized atoms 6KOH + 3MnO2 + 6KClO3 get entrapped in between the interstitial spaces of 3K2MnO9 + 6KCl + 3H2O the metal Lattices. o The potassium manganate (green) so formed is boiled These interstitial compounds are non stoichiometric with a large quantity of water and current of chlorine, in nature and hence cannot be given any definite CO2 and ozonized air is passed into the liquid until it formula. is converted into permanganate. The MnO2 formed is removed continuously in order to prevent its The smaller sized elements are held in interstitial breaking down the permanganate. spaces of transition elements by weak Vander Waals 6K2MnO4 + 3Cl2 forces of attractions.  6KMnO4 (Potassium Permanganate) + 6KCl The interstitial compounds have essentially the same chemical properties as the parent metals but they The solution of KMnO4 is drawn off from any differ in physical properties such as density and precipitate of MnO2 concentrated and crystallized. The crystals are centrifuged and dried. hardness. 2. o o o o 80 Physical Properties of Potassium Permanganate KMnO4 o It is an odourless, purple to magenta crystalline solid. o It is soluble in water, acetone, acetic acid, methanol, and pyridine. o It gets dissolved in ethanol and organic solvents. o Potassium permanganate occurs in the form of monoclinic prisms, almost opaque with a blue metallic luster. 4. The d and f Block Elements Oxidizing properties KMnO4 acts as a very powerful oxidizing agent in acidic, neutral and alkaline media. The equations representing oxidation in these media are In acidic medium 2KMnO4 + H 2SO 4  K 2SO 4 + 2MnSO 4 + 3H2O + 5[O] MnO4- + 8H+ + 5e Mn2+ + 4H2O In neutral or alkaline medium 2KMnO4 + H2O  2KOH + 2MnO2 + 3[O] MnO4- + 2H2O + 3e-  MnO2 + 4OH- It is odourless. An aqueous solution has a sweetish astringent taste. It is water-soluble and more soluble Uses Of Potassium Permanganate (KMnO4) in boiling water. There are wide applications of KMnO4. Some Chemical Properties Of Potassium Permanganate important uses of potassium permanganate have o Very strong oxidizing agent and used for this reason been discussed below: in many reactions o It is used in qualitative analysis to determine the permanganate value o It can be seen while performing the redox reaction, in which the dark purple solution turns colourless o It is used in as a regeneration chemical in well water treatment to remove hydrogen sulfide and iron and then into a brown solution. o The above reaction can be performed in an acid or o It is used as a disinfectant to cure skin conditions like foot fungal infections, dermatitis a base Reactions Of Potassium Permanganate (KMnO4) o It is used in the treatment of bacterial infections o It is used in tanning leathers, printing fabrics 1. Thermal decomposition: o It is used as bleach, pesticide, antiseptic When solid potassium permanganate is heated it o It is used in industries as an oxidizing agent undergoes decomposition. The reaction is as follows: o 2KMnO4  K2MnO4 + MnO2(s) + O2 2. Reaction with acid: When permanganate reacts with concentrated hydrochloric acid it produces chlorine. In a neutral solution, permanganate is reduced by three electrons to produce manganese dioxide, where the oxidation state of manganese is +4. Potassium permanganate reduces spontaneously in an alkaline solution and turns into green K2MnO4. 3. Effect of Alkalies On heating with alkalies, potassium permanganate changes into manganate and oxygen gas is evolved. 4KMnO4 + 4KOH  4K2MnO4 + 2H2O + O2 POTASSIUM DICHROMATE K2Cr2O7 o Potassium compounds are quite common and are extremely useful for a variety of purposes. Potash and other potassium compounds have been used for centuries in the manufacture of glass products. Today 95% of the potassium compounds gathered in the world is used in the manufacture of fertilizers. o Potassium dichromate is an inorganic chemical compound possess immense industrial and laboratory importance. It is an orange crystalline solid with the chemical formula K2Cr2O7. It is a strong oxidising agent and is soluble in water. It is used in the volumetric estimation of ferrous salts, iodides and sulphides for the preparation of chrome alum, chrome yellow and chrome red. 81 What is Potassium dichromate (K2Cr2O7)? o o o o The d and f Block Elements Potassium dichromate (K2Cr2O7 ) Uses K2Cr2O7 is an inorganic chemical reagent with o chemical name Potassium dichromate. It is also called as Potassium bichromate or Dipotassium bichromate. o It is crystalline ionic solid, with a bright red-orange o colour. It is odourless and insoluble in acetone as well as alcohol but dissolves in water. o It is widely used as a precursor to potassium chrome alum and leather tanning. It is commonly used as an o oxidizing agent in several industries and laboratories. It is highly corrosive and noncombustible. Potassium o dichromate is prepared as follows By reacting potassium chloride on sodium dichromate or Produced from potassium chromate by the roasting of chromite ore with potassium hydroxide o Used in cement to retard the setting of the mixture and to improve its density along with the texture. It is used in photographic screen printing. It is a common reagent used in analytical chemistry for classical "wet tests". It is used to stain certain type of woods to produce deep, rich browns. It is used to clean glassware and as an etching material. Used in pyrotechnic displays along with iron and tungsten. Medically it can be used externally as an antiseptic, caustic, and astringent. Potassium dichromate Structure (K2Cr2O7 Structure) Potassium dichromate Structure 82