Tiêu đề SP-4_Ch-21-The d- and f-Block Elements.pdf ✅

Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents Introduction Position in the Periodic Table Electronic Configurations of the d-Block Elements General Properties of the Transition Elements (d-Block) Some Important Compounds of Transition Elements The Inner Transition Elements The Lanthanoids The Actinoids Some Applications of d & f-Block Elements Introduction Classification of elements in blocks is based on their characteristic properties. During filling of electrons the last electron decides the block of the element. d-block contains 3 to 12 group. A number of compounds of this block elements are important catalyst in industry. These elements attract special attention of chemists because of their special chemistry. In this chapter, we are going to study the usual and unusual properties of these elements which make them so important. POSITION IN THE PERIODIC TABLE The d-block of the periodic table contains the elements of group 3-12 in which the d orbitals are progressively filled in each of the four long periods. The name “transition” given to the element of d-block is only because of their position between s and p-block elements. There are four series of the transition metals 3d series (Sc to Zn), 4d series (Y to Cd) and 5d (La, Hf to Hg) and 6d series (Ac, unq to Uub). Definition of Transition Element A transition element is defined as the one which has incompletely filled d orbitals in its ground state or in their most common oxidation state. Zn, Cd and Hg are not typical transition elements because they have full d10 configuration in their ground state as well as in their common oxidation state. However, being the last members of three transition series, their chemistry is studied along with the chemistry of transition metals. Chapter 21 The d- and f-Block Elements
42 The d- and f-Block Elements NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 ELECTRONIC CONFIGURATIONS OF THE d-BLOCK ELEMENTS General E.C. of the d-block element is as For 3d series 3d1 – 10 4s1 – 2 For 4d series 4d1 – 10 5s0 – 2 Overall ( – 1) n d ns 1 – 10 0 – 2 For 5d series 5d1 – 10 6s1 – 2 For 6d series 6d1 – 10 7s1 – 2 Outer Electronic Configurations of the Transition Elements (ground state) Sc Ti V Cr Mn Fe Co Ni Cu Zn Z 21 22 23 24 25 26 27 28 29 30 4s 2 2 2 1 2 2 2 2 1 2 3d 1 2 3 5 5 6 7 8 10 10 1st Series Y Zr Nb Mo Tc Ru Rh Pd Ag Cd Z 39 40 41 42 43 44 45 46 47 48 5s 2 2 1 1 1 1 1 0 1 2 4d 1 2 4 5 6 7 8 10 10 10 2nd Series La Hf Ta W Re Os Ir Pt Au Hg Z 57 72 73 74 75 76 77 78 79 80 6s 2 2 2 2 2 2 2 1 1 2 5d 1 2 3 4 5 6 7 9 10 10 3rd Series Ac Rf Db Sg Bh Hs Mt Ds Rg Uub Z 89 104 105 106 107 108 109 110 111 112 7s 2 2 2 2 2 2 2 2 1 2 6d 1 2 3 4 5 6 7 8 10 10 4th Series However, this generalisation has several exceptions because of very little energy difference between (n – 1)d and ns orbitals. Furthermore half filled and fully filled sets of orbitals are relatively more stable. Apart from it as Z* increases energy gap between (n – 1)d and ns decreases, which is small enough to prevent electron entering in (n – 1)d before completely filling of ns. The d orbitals of the transition element project to the periphery of an atom more than the other orbitals (s and p). Hence, they are more influenced by the surrounding as well as affecting the atoms or molecules surrounding them. Example 1 : On what ground can we say that Sc(Z = 21) is a transition element while Zn(Z = 30) is not? Solution : E.C. of 21Sc = 1s2 2s2 2p6 3s2 3p6 3d1 4s2. In this E.C. 3d orbital have one electron in its ground state. That is why it is regarded as a transition element. E.C. of Zn = 1s2 2s2 2p6 3s2 3p6 3d10 4s2 Zn does not have partly filled d orbital in its ground state or in its excited state that is why it is not considered as a typical transition element.
NEET The d- and f-Block Elements 43 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Example 2 : Copper atom has completely filled d orbitals (4d10) in its ground state. How can we say that it is a transition element? Solution : Transition element is defined as the one which has incompletely filled d orbitals in its ground state or in their most common oxidation state. Cu in its +2 oxidation state exhibit 4d9 E.C. That is why it is considered as a transition element. Note : As per rule (Aufbau Rule) last electron is filled in 3d after filling of 4s in Fe. But during removal last electron is removed from ultimate shell that is (4s) and hence E.C. of Fe2+ is 1s2 2s2 2p6 3s2 3p6 3d6. Aufbau Rule or (n + l) Rule is only valid for unfilled orbital. After filling of the electron in E.C. higher will be value of n higher will be energy and if value of n is same then higher will be value of l higher will be energy. For s orbital, l = 0 p, l = 1 d, l = 2 f, l = 3 GENERAL PROPERTIES OF THE TRANSITION ELEMENTS (d-BLOCK) Physical Properties Nearly all the transition elements display metallic properties such as high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre. Note : Except Zn, Cd, Hg and Mn, other metals have one or more typical metallic structure at normal temperature. Lattice Structures of Transition Metals Sc Ti V Cr Mn Fe Co Ni Cu Zn Y Zr Nb Mo Tc Ru Rh Pd Ag Cd La Hf Ta W Re Os Ir Pt Au Hg hcp hcp bcc bcc X bcc ccp ccp ccp X (bcc) (bcc) (hcp) (hcp) hcp hcp bcc bcc hcp hcp ccp ccp ccp X (bcc) (bcc) (hcp) hcp hcp bcc bcc hcp hcp ccp ccp ccp X (ccp,bcc) (bcc) (bcc, ccp) (hcp) (bcc = body centred cubic; hcp = hexagonal close packed; ccp = cubic close packed; X = a typical metal structure). The transition metals (with the exception of Zn, Cd, Hg) are very 1 2 3 4 M.p./10 K3 Ti Zr Hf W Re Ta Os Ir Ru Mo Nb Tc Rh Cr V Mn Fe Co Ni Pd Pt Cu Au Ag Atomic number Trends in melting points of transition elements much harder and have low volatility. Their melting points and boiling points are high. The high melting points of these metals are attributed to involvement of greater number of electrons from (n – 1)d in the addition to ns electrons in the interatomic metallic bonding. In any row the melting points of these metals rise to maximum at d5 except for anamolous behaviour of Mn and Tc and fall regularly as the atomic number increases. They have high enthalpies of atomisation which is shown in figure.
44 The d- and f-Block Elements NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 In general greater the number of valence electrons, stronger is the resultant bonding. Since the enthalpy of atomisation is an important factor in determining the standard electrode potential of a metal, metals with very high enthalpy of atomisation i.e., very high boiling point tend to be noble in their reactions. Another generalisation that may be drawn that metals of the 2nd and 3rd series have greater enthalpies of atomisation than the corresponding elements of 1st series. This is an important factor in accounting for the occurrence of much more frequent metal-metal bonding in compounds of heavy transition metals. Electronic Configurations and some other Properties of the First Series of Transition Elements Element Sc Ti V Cr Mn Fe Co Ni Cu Zn Atomic number Electronic configuration Enthalpy of atomisation, H kJ mol Ionisation enthalpy/ H kJ mol Metallic/ionic radii/pm Standard electrode potential E /V Density/g cm 21 22 23 24 25 26 27 28 29 30 M 34 34 34 34 34 34 34 34 3 4 3 4 M 34 34 34 3 34 34 34 34 3 3 4 M3 3 3 3 3 3 3 3 3 3 M [Ar] 3 3 3 3 3 3 3 – – 326 473 515 397 281 416 425 430 339 126 I 631 656 650 653 717 762 758 736 745 906 II 1235 1309 1414 1592 1509 1561 1644 1752 1958 1734 III 2393 2657 2833 2990 3260 2962 3243 3402 3556 3829 M 164 147 135 129 137 126 125 125 128 137 M – – 79 82 82 77 74 70 73 75 M 73 67 64 62 65 65 61 60 – – M /M – –1.63 –1.18 –0.90 –1.18 –0.44 –0.28 –0.25 +0.34 –0.76 M /M – –0.37 –0.26 –0.41 +1.57 +0.77 +1.97 – – – 3.43 4.1 6.07 7.19 7.21 7.8 8.7 8.9 8.9 7.1 ds ds ds ds ds ds ds ds d s d s ds ds ds d ds ds ds ds d d s d d d d d d d d dd dddd d dd 1 2 2 2 3 2 5 1 5 2 6 2 7 2 8 2 10 1 10 2 + 1 1 2 1 3 1 5 5 1 6 1 7 1 8 1 10 10 1 2+ 1 2 3 4 5 6 7 8 9 10 3+ 1 2 3 4 5 6 7 2+ 3+ 2+ 3+ 2+   a i s –1 –1 –3 s s s s s    i i i H H H Atomic and Ionic size In general, ions of the same charge in given series show progressive decrease in radius with increasing atomic number. This is because the new electron enters a d orbital each time the nuclear charge increases by unity and shielding effect of d electron is not effective hence net electrostatic attraction between the nuclear charge and outer most electron increases and the ionic radius decreases. This same trend is observed in the atomic radii of a given series. However the variation within a series is quite small. Elements of 4d series have larger size than 3d but size of 4d and 5d elements is nearly same in a group. This is due to poor screening of 4f electrons. 19 18 16 15 13 12 Sc Ti V Cr Mn Fe Co Ni Cu Zn Y Zr Nb Mo Pd Ag Cd La Hf Ta W Re Os Ir Pt Au Hg Radius/nm 17 14 Trends in atomic radii of transition elements Tc Ru Rh