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5. (a) How is group, period and block of elements predicted. (b) Give the electronic configuration and in terms of period group and block where would you locate the elements with Z= 17, 19. 24, 26, 29, 31,34,38, 40, 51,55,114 ,117 and 120 ?

Answer»

PREDICTION of PERIOD ======================= In the electronic configuration of an atom , the principal quantum number of VALANCE electron REPRESENTS the PERIOD of the element . example :- Ca ( atomic no = 20 ) configuration of Ca : 1s², 2s² , 2p^6 , 3s² , 3p^6, 4s² . valance electrons = 2 { in 4S } Principal Quantum no = 4 hence, period of Ca is 4th PREDICTION of GROUP ====================== The orbital { S, P , d , or F } which receives the last electton represents the block of the element. ➡ The group of the element is PREDICTED from the block of the elements as : - (1) if the element belongs to S - block , it's group number is equal to the number of valance electrons . (2) if the element belongs to P -block , Group number = 10 + number of valance electrons = 10 +nS electrons + nP electrons (3) if the elements belongs to d -block , Group number = number of electrons in (n -1)d subshell + number of electrons in nS subshell . (4) if the element belong to f - subshell , group number is always 3 . (((b))) Z = 17 configuration : 1s² , 2s² , 2p^6, 3s², 3P^5 hence, Period : 3rd group : 10 + 2 + 5 = 17th Z = 19 configuration : 1s² , 2s² , 2p^6, 3s² , 3p^6 , 4s¹ period : 4th group : 1st Z = 24 configuration: 1s², 2s² , 2p^6, 3s² , 3P^6, 3d^5 , 4s¹ period : 4th group : 6th Z = 26 configuration: 1s² , 2s² , 2P^6, 3s² ,3P^6, 3d^6, 4s² period : 4th group : 8th Z = 29 configuration : [Ar] 3d^10 , 4s¹ period : 4th group : 11th Z = 31 configuration: [Ar]3d^10, 4s², 4P¹ period : 4th group : 13th Z = 34 configuration : [Ar] 3d^10, 4s², 4P^4 period : 4th group: 16th Z = 38 Configuration: [Kr] 4d^2 period : 4th group: 2nd Z = 40 configuration: [Kr]4d^4 period :4th group : 4th Z = 51 configuration: [Kr]4d^10, 5s², 5P^ 3 period : 5th group: 15th Z = 55 configuration: [Xe] 6s¹ period : 6th group : 1st Z =114 configuration : [Rn]7s², 5f^14, 6d^10,7p² period : 7th group : ( 2 + 10 + 2) th = 14th Z = 117 configuration : [Rn]7s², 5f¹⁴, 6d^10, 7P^5 period : 7th in periodic table only 118 elements exist . 120 elements location can't possible in Morden periodic table .


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