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Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 Chapter Contents Genesis of Periodic Classification Modern Periodic Table Nomenclature of Elements with atomic number > 100 Classification of elements on the basis of electronic configuration Periodic Trends in Physical Properties Electron Gain Enthalpy Electronegativity Diagonal Relationship Periodic Trends and Chemical Reactivity Chapter 3 Classification of Elements and Periodicity in Properties GENESIS OF PERIODIC CLASSIFICATION Dobereiner grouped elements in triads e.g. Li, Na, K or Cl, Br, I etc. Newland found that similar elements are repeated at 8th place. It happened when elements were arranged in the increasing order of their atomic masses. Lother Mayer plotted a graph between atomic volume of elements against their atomic weight. He found that similar elements occupied similar positions on the curve. Mendeleev’s Periodic Law and Table: Mendeleev arranged all the elements in order of their increasing atomic weights. A table which has been formed with the help of classification of elements is called periodic table. The method of arranging similar elements in one group and separating them from dissimilar element is called classification of elements. Mendeleev prepared the table on the basis of his periodic law called Mendeleev’s periodic law. According to which ‘‘the physical and chemical properties of elements are the periodic function of their atomic weights.’’ MODERN PERIODIC TABLE It based on modern periodic law given by Moseley. The modern periodic law is stated as “The properties of elements are periodic function of their atomic number.”
56 Classification of Elements and Periodicity in Properties NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 Extended or Long form of Periodic Table 3 Li 2s 1 4 Be 2s 2 11 Na 3s 1 12 Mg 3s 2 3 III B 4 IV B 5 V B 6 VI B 7 VII B 9 VIII 11 I B 8 10 12 II B 13 Al 3s 2 3p 1 14 Si 3s 2 3p 2 15 P 3s 2 3p 3 16 S 3s 2 3p 4 17 Cl 3s 2 3p 5 5 B 2s 2 2p 1 6 C 2 2 s p 2 2 7 N 2 2 s p 2 3 8 O 2 2 s p 2 4 9 F 2 2 s p 2 5 1 I A 2 II A 13 III A 14 IV A 15 V A 16 VI A 17 VII A 19 K 4s 1 20 Ca 4s 2 21 Sc 3 4 d s 1 2 22 Ti 3 4 d s 2 2 23 V 3 4 d s 3 2 24 Cr 3 4 d s 5 1 25 Mn 3 4 d s 5 2 26 Fe 3 4 d s 6 2 27 Co 3 4 d s 7 2 28 Ni 3 4 d s 8 2 29 Cu 3 4 d s 10 1 30 Zn 3 4 d s 10 2 31 Ga 4 4 s p 2 1 32 Ge 4 4 s p 2 2 33 As 4 4 s p 2 3 34 Se 4 4 s p 2 4 35 Br 4 4 s p 2 5 37 Rb 5s 1 38 Sr 5s 2 39 Y 4 5 d s 1 2 40 Zr 4 5 d s 2 2 41 Nb 4 5 d s 4 1 42 Mo 4 5 d s 5 1 43 Tc 4 5 d s 5 2 44 Ru 4 5 d s 7 1 45 Rh 4 5 d s 8 1 46 Pd 4d10 47 Ag 4 5 d s 10 1 48 Cd 4 5 d s 10 2 49 In 5 5 s p 2 1 50 Sn 5 5 s p 2 2 51 Sb 5 5 s p 2 3 52 Te 5 5 s p 2 4 53 I 5 5 s p 2 5 55 Cs 6s 1 56 Ba 6s 2 57 La* 5 6 d s 1 2 72 Hf 456 f ds 14 2 2 73 Ta 5 6 d s 3 2 74 W 5 6 d s 4 2 75 Re 5 6 d s 5 2 76 Os 5 6 d s 6 2 77 Ir 5 6 d s 7 2 78 Pt 5 6 d s 9 1 79 Au 5 6 d s 10 1 80 Hg 5 6 d s 10 2 81 Tl 6 6 s p 2 1 82 Pb 6 6 s p 2 2 83 Bi 6 6 s p 2 3 84 Po 6 6 s p 2 4 85 At 6 6 s p 2 5 87 Fr 7s1 88 Ra 7s2 89 Ac** 6 7 d s 1 2 104 Rf 105 Db 106 Sg 107 Bh 108 Hs 109 Mt 110 Ds 111 Uuu 112 Uub 114 Fl Inner transition elements 58 Ce 45 6 fds 2 02 59 Pr 45 6 fds 3 02 60 Nd 45 6 fds 4 02 61 Pm 45 6 fds 5 02 62 Sm 45 6 fds 6 02 63 Eu 45 6 fds 7 02 64 Gd 45 6 fds 7 12 65 Tb 45 6 fds 9 02 66 Dy 4 56 f ds 10 0 2 67 Ho 456 f ds 11 0 2 68 Er 4 56 f ds 12 0 2 69 Tm 4 56 f ds 13 0 2 70 Yb 4 56 f ds 14 0 2 90 Th 56 7 fds 0 22 91 Pa 56 7 fds 2 12 92 U 56 7 fds 3 12 93 Np 56 7 fds 4 12 94 Pu 56 7 fds 6 02 95 Am 56 7 fds 7 02 96 Cm 56 7 fds 7 12 97 Bk 56 7 fds 9 02 98 Cf 5 67 f ds 10 0 2 99 Es 567 f ds 11 0 2 100 Fm 5 67 f ds 12 0 2 101 Md 5 67 f ds 13 0 2 102 No 5 67 f ds 14 0 2 *Lanthanoids 4 5 6 fd s n 0 –1 2 **Actinoids 5 6d 7 f s n 0–2 2 GROUP NUMBER Representative elements GROUP NUMBER Transition elements 1 H 1s 1 GROUP NUMBER PERIOD NUMBER 1 2 3 4 5 6 7 Representative elements Long form of the Periodic Table of the Elements with their atomic numbers and ground state outer electronic configurations. The groups are numbered 1-18 in accordance with the 1984 IUPAC recommendations. This notation replaces the old numbering scheme of IA–VIIA, VIII, IB–VIIB and 0 for the elements. 103 Lr 5 67 f ds 14 1 2 71 Lu 4 56 f ds 14 1 2 18 Ar 3s 2 3p 6 10 Ne 2 2 s p 2 6 2 He 1s 2 36 Kr 4 4 s p 2 6 54 Xe 5 5 s p 2 6 86 Rn 6 6 s p 2 6 18 0 Noble gases 113 Nh 115 Mc 116 Lv 117 Ts 118 Og NOMENCLATURE OF ELEMENT WITH ATOMIC NUMBER > 100 The IUPAC proposed a system for naming element with Z > 100. The name are derived by using roots for the three digits in the atomic number of the element and adding the ending - ium. The roots for the numbers are: 0 1 2 3 4 5 6 7 8 9 nil un bi tri quad pent hex sept oct enn In certain cases the names are shortened; for example, bi ium and tri ium are shortened to bium and trium, and enn nil is shortened to ennil. The symbol for the element is made up from the first letters from the roots which make up the name. The strange mixture of Latin and Greek roots has been chosen to ensure that the symbols are all different. Though the names are written as a complete word, in the examples below a hyphen has been inserted between each part of the name to make them more understandable. These hyphens should be omitted.
NEET Classification of Elements and Periodicity in Properties 57 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 IUPAC nomenclature for the superheavy elements : At. No. Atomic Name Symbol At. No. Atomic Name Symbol 101 un-nil -unium Unu 112 un-un-bium Uub 102 un-nil -bium Unb 113 un-un-trium Uut 103 un-nil -trium Unt 114 un-un-quadium Uuq 104 un-nil -quadium Unq 115 un-un-pentium Uup 105 un-nil -pentium Unp 116 un-un-hexium Uuh 106 un-nil -hexium Unh 117 un-un-septium Uus 107 un-nil -septium Uns 118 un-un-octium Uuo 108 un-nil -octium Uno 119 un-un-ennium Uue 109 un-nil -ennium Une 120 un-bi-nilium Ubn 110 un-un-nillium Uun 130 un-tri -nilium Utn 111 un-un-unnium Uuu 140 un-quad-nilium Uqn 150 un-pent-nilium Upn Note : Hyphens have been put in the name for clarity. They should be omitted. Example 1 : What would be the IUPAC name and symbol for the element with atomic number 120? Solution : The root for 1, 2 and 0 are un, bi and nil respectively. Hence, the name becomes unbinilium and the symbol is Ubn. CLASSIFICATION OF ELEMENTS ON THE BASIS OF ELECTRONIC CONFIGURATION On the basis of electronic configuration the elements can be classified into the following four types : (i) s-block elements : These elements contain 1 or 2 electrons in s-subshell of outermost shell. Elements of 1 and 2 group belong to this class. These elements enter into chemical reaction by losing valency electrons so as to acquire noble gas configuration in the outermost orbit. ns1 (group 1) ns2 (group 2) (alkali metals) (alkaline earth metals) These elements generally form electrovalent compounds and basic oxides. (ii) p–block elements : These elements contain 1 to 6 electrons in the p–subshell of the outermost orbit (ns2 np1–6). The elements belonging to 13th to 18th group are p-block elements. In these last electron enters to the p-subshell. For example. 13 Boron (B) Z = 5 1s2 2s2 2p1 14 Carbon (C) Z = 6 1s2 2s2 2p2 15 Nitrogen (N) Z = 7 1s2 2s2 2p3 16 Oxygen (O) Z = 8 1s2 2s2 2p4 17 Fluorine (F) Z = 9 1s2 2s2 2p5 The main characteristics of these elements are : (a) The non-metallic character increases along a period from 13 to 17. (b) They form covalent compounds among themselves but electrovalent compounds with s-block elements.
58 Classification of Elements and Periodicity in Properties NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 (iii) d–block elements : These are called transition elements or ‘d’ block elements. The elements of group 3 to 12 belong to this class. Their general configuration can be represented as : (n–1)d1–10 ns0–2 General characteristics of transition (d–block) elements: (a) They are metals, hard, malleable, ductile and possess high tensile strength. (b) They are good conductors of heat and electricity. (c) These elements exhibit variable valency. (d) They generally form coloured compounds. (e) These metals, their alloys and compounds possess marked catalytic activity. (iv) f–block elements : They are inner transition or f-block elements. These elements are arranged in the two rows at the bottom of the periodic table. In the first row, there are 14 elements from atomic number 58 to 71, known as Lanthanides or rare earth elements. The second row of elements from atomic number 90 to 103, known as actinides. Their general electronic configuration can be represented as (n – 2) f 1–14 (n–1)d 0–1 ns2 They show most of the properties similar to each other since outermost and penultimate orbits are similar. Their properties are similar to ‘d’ block elements. EXERCISE 1. All the elements in a group in the periodic table have the same (1) Atomic number (2) Electronic configuration (3) Atomic weight (4) Number of electrons in the valence shell 2. Atomic number of element present in the third period and seventeenth group of periodic table (1) 15 (2) 16 (3) 9 (4) 17 3. Chalcogen are elements of the group (1) 17th (2) 15th (3) 16th (4) 14th 4. Representative elements are elements of (1) s-block (2) s-block and p-block (3) d-block or transition elements (4) d-block and f-block 5. Which general electronic configuration of the element does not represent a non-metal? (1) ns2, np4 (2) ns2, (n – 1)d1 – 10, np5 (3) ns1–2, (n – 1) d1–10 (4) ns2, (n – 1)d1 – 10, np1– 6 6. Number of groups in d-block (1) 5 (2) 10 (3) 15 (4) 20 PERIODIC TRENDS IN PHYSICAL PROPERTIES Atomic Radii Atomic radius is the size of the atom of an element. Atomic radius is defined as “the distance from the centre of the nucleus upto the centre of outermost electron”. It is measured in Angstrom unit (Å). It is not possible to measure exact atomic radius as an atom is unstable and it cannot be isolated to get its radius. Moreover,