7 inch 2.5 inch PERIODIC PROPERTIES 2.5 inch 2.5 inch I NDEX Topic Page No. INORGANIC CHEMISTRY PERIODICPROPERTIES 1. Classification of Elements and Periodicityin properties 01 2. Mendeleev’s Periodic Law 03 3. Modern Periodic Law 07 4. Effective Nuclear Charge 11 5. AtomicSize 12 6. IonisationPotential 15 7. ElectronAffinity 18 8. Electronegativity 20 9. Density 27 10. DiagonalRelationship 28 11. Metallic Character 28 12. Non-metallic character 29 PERIODIC PROPERTIES Topic Page No. 13. Reactivity,Oxidation state,Valency 29 14. Acid-base behaviour of oxides and hydroxides 30 15. Atomicvolume 30 16. Graphs of periodic properties 30 17. General Trend of different properties in the period and groups 35 18. Important facts of remember 36 19. Solved Examples 38 20 Exercise - 1 41 Exercise - 2 46 Exercise - 3 51 Exercise - 4 55 21. Answer Key 58 22. Hints/Solution 60 ACC- CH-PERIODIC PROPERTIES 1 PERIODIC PROPERTIES CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES Need for classification: It is verydifficult to studyindividuallythechemistryofall the elements and millionsoftheircompounds, hence to simplifyand systematize the studyof chemistryof the elements and their compounds, theyare classified into groups and periods. Earlyattempt to classifythe elements: Classification of Lavoiser Elements had been classified into two major groups by Lavoiser 1. Metals 2. Non–metals This classification was based on the differences in their properties. The metal word itself can be considered an acronym in which each alphabet signifies a characteristic of these substances: 1. M = malleability.The most malleable beingAu and Pt. s–block < p–block < d–block > f–block. M = meltingpoint (also boiling point)of the metals in general is high. Metal havingthehighest melting pointisTungsten(W)andthehighestboilingpointisRenium(Re).ThelowestmeltingpointisofMercury (Hg) and it is one of the two elements in the periodic table which are liquid at 25oC. (The other being Bromine). The element havinghighest mp isW. Element having lowest mp and bp is He. 2. E stands forelasticity(Young’smodulus) E is also for electropositive. E also for good conductors ofElectricity.Best isAg> Cu >Au. Metals are good conductors of electricity and heat due to the presence of free mobile delocalized electrons. Graphite and black phosphorous are also conductors of electricity but not of heat. Whenever a compound of metal is electrolysed metal always deposited at cathode while non metal at both anode as well as cathode. 3. T=Tenacity(Tensile/ductile means elongation)Most tensile/ductile–Au/Pt. Least – Pb T =Toughness/ Hardness. Hardest is W. Exception : diamond is the hardest material ever known. Synthetic hard materials are called abrasive. These are CorundumAl2O3, Carborundum SiC, Borazone BN, Boron carbide B4C (non stoichiometric),Tantalum Carbide and Tungsten Carbide as hard as diamond. 4. A=Allotropy/polymorphism, shown mainlybynonmetals. Metals such as Sn show polymorphism. =Atomicity,Number ofatoms inthemoleculeof anelement.Atomictyis verysignificant for non–metals because it reveals the shape of the molecules and physical properties (state) of the molecules. A=Alloys formation. BANSAL CLASSES Private Ltd. ‘Gaurav Tower’, A-10, Road No.-1, I.P.I.A., Kota-05 2 ACC- CH-PERIODIC PROPERTIES Alloys are homogeneous mixture of two or more metals. It mayalso have some non metals as well. Everyalloyisasolid solution exceptthealloys ofHgwhich is asolution ofasolid into aliquid. Thealloys ofmercuryarecalledamalgum.Alloysofmetalswithatleastanon–metalarecalledinterstitialcompounds. Alloys of only metals of nearly similar character are called substitutional compounds. Steel is a homogeneous mixture. It also is an interstitial compound. Purpose of alloying a metal are: a. To increase the utilityof the metals eg. fuse wire (Pb+ Sn + Bi). It melts in boiling water. b. To increase the hardness. Alloying is propertyof metals not of nonmetals. 5. L = lustre, Shine property of metals. Each metal having a characteristic. 6. S = sonorous. Each metal gives special sound on beating. Dobereiner’s law of traids: It was first attempt towards classification. He arranged similar elements in a group of three elements called triad and the atomic mass of the middle elements of the traid is approximately the arithmetic mean of the other two. e.g. Ca40 Sr87.5 Ba137 40137 At. wt. of Sr = 5.88 2 88.5 is nearly similar to 87.5 of atomic wt. of Sr. Such a group of elements is called Dobereiner’s triad. Triad of atoms Mean of first and last element 7 39 Li Na K 23 2 7 23 39 8 40 Be Mg Ca 24 2 8 24 40 Dobereiner could arrange only a few elements as triads and there are some such elements present in a triad, whose atomic weights are approximatelyequal, e.g. Fe Co Ni Ru Rh Pd There fore, this hypothesis was not acceptable for all elements. Newland’s law of octaves: When the lighter elements are arranged in order of their increasing atomic weights, then every eighth element is similar to the first element in its properties, similarly as the eighth node of a musical scale is similar to 1st one. e.g. Na 8th element resembles in their properties with Li. Similarly K the 8th element with Na and so on. BANSAL CLASSES Private Ltd. ‘Gaurav Tower’, A-10, Road No.-1, I.P.I.A., Kota-05 ACC- CH-PERIODIC PROPERTIES 3 Name of element Li Be B C N O F 7 9 11 12 14 16 19 Name of element Na Mg Al Si P S Cl 23 24 27 28 31 32 35.5 It is clearfrom the abovetablethat sodium is theeighth element from lithium, whoseproperties resemble thatoflithium. This type ofclassification was limited up to only20 elements. Inert gas element were not discovered till then. Lother Meyer arrangement: Cs Rb K Br e Na Ca m u l Li Cl o Sr I V Ba c i F m Be o t Mg A Metalloid and transition metals Atomic Weight The graphs plotting the atomic volumes against atomic weights are known as Lothar Mayer volume curves. The alkali metalshavehighest atomicvolumes. Alkaline earth metals (Be, Mg Ca, Sr, Ba, etc.) which are relativelya little less electropositive. Occupy positions on the descending part of the curve. Halogens and the noble gases (except helium) occupy positions on the ascending part of the curve. Transition elements have verysmall volumes and therefore these are present at the bottoms of the curve Exercise 1. Lother Meyer attempt was based on plotting atomic mass vs (A)Atomicsize (B)Atomicvolume (C) Density (D)Meltingpoint Ans. (B) MENDELEEV’S PERIODIC LAW (i) Mendeleev’s Periodic Law - The physical and chemical properties of elements are the periodic function of their atomic weight (ii) Characteristic of Mendeleev’s Periodic Table - (a) It is based on atomic weight (b) 63 elements were known, noble gases were not discovered. (c) 12 Horizontal rows are called periods. (d) Vertical columns are called groups and there were 8 groups in mendeleev’s Periodic table. (e) Each group upto VIIth is divided intoA& B subgroups. ‘A’sub groups element are called normal elements and ‘B’sub groups elements are called transition elements. (f) The VIIIth group was consists of 9 elements in three rows (Transition metals group). (g) The elements belonging to same group exhibit similar properties. BANSAL CLASSES Private Ltd. ‘Gaurav Tower’, A-10, Road No.-1, I.P.I.A., Kota-05 4 ACC- CH-PERIODIC PROPERTIES MODIFIED MENDELEEF’S PERIODIC TABLE OF ELEMENTS BANSAL CLASSES Private Ltd. ‘Gaurav Tower’, A-10, Road No.-1, I.P.I.A., Kota-05 ACC- CH-PERIODIC PROPERTIES 5 (iii) Merits or advantages of Mendeleev’s periodic table - (a) Study of elements - First time all known elements were classified in groups according to their similar properties. So study of the properties become easier of elements. (b) Prediction of new elements - It gave encouragement to the discovery of new elements as some gapswereleftinit.Sc(Scandium),Ga(Gallium),Ge(Germanium),Tc(Technetium)weretheelements for whom position and properties were defined byMendeleev even before their discoveries and he left the blank spaces for them in his table. e.g.- Blank space at atomic weight 72 in silicon group was called Eka silicon (means properties like silicon) and element discovered later was named Germanium. Similarlyother elements discovered after mendeleev periodic table were. Ekaaluminium-Gallium(Ga) Eka Boron - Scandium (Sc) Eka Silicon - Germanium (Ge) Eka Manganese -Technetium (Tc) (c) Correction of doubtful atomic weights - Correction weredone in atomic weight of some elements. AtomicWeight =Valency× Equivalent weight. Initially,it was found that equivalent weight of Be is 4.5and it is trivalent (V= 3), so theweight of Be was 13.5 and there is no space in Mendeleev’s table for this element. So, after correction, it was found that Be is actually divalent (V = 2). So, the weight of Be became 2 × 4.5 = 9 and there was a space between Li and B for this element in Mendeleev’s table. – Corrections were done in atomic weight of elements are – U, Be, In,Au, Pt. (iv) Demerits of Mendeleev’s periodic table - (a) Position of hydrogen - Hydrogen resembles both, thealkali metals (IA)and the halogens (VIIA) in properties so Mendeleev could not decide where to place it. (b) Position of isotopes -As atomic weight of isotopes differs, they should have placed in different position in Mendeleev’s periodic table. But there were no such places for isotopes in Mendeleev’s table. (c) Anomalous pairs of elements - There were some pair of elements which did not follow the increasing order of atomic wts. eg. Ar and Co were placed before K and Ni respectivelyin the periodic table, but having higher atomic weights. Ar K Te I Co Ni Th Pa 39.9 39.1 127.5 127 58.9 58.6 232 231 (d) Like elements were placed in different groups.