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Classification of elements


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Classification of al elements & their periodicty and different trends in their properties, also an overview over the development of periodic table during 18 and 19 centuries

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Classification of elements

  1. 1. After this lecture you will be able to : • Understand the significance of classification. • Know about the history of development of periodic table. • Understand the modern periodic law & present form of periodic table. • Learn the various periodic trends in properties of elements.
  2. 2. • Rapid development during the 18th and 19th century including the discovery of several new elements. • This gave rise to need of classification of elements into groups with similar properties. • Thus, classification of elements resulted in the formulation of periodic table.
  3. 3. • Father of the Periodic Table • Periodic Law- Both physical and chemical properties of the elements vary periodically with increasing atomic mass. • Exception placed Te (M = 127.6) a head of I (M=126.9) because Te was similar to Se and S, and I was similar to Cl and Br. • Left gaps in periodic table and predicted new elements would be found. Predicted the new elements’ properties.
  4. 4. Utility of Mendeleev’s Periodic Table • Systematic study of elements • Prediction of new elements • Correction of atomic masses • Use in research Defects of Mendeleev’s Periodic Table • Position of Hydrogen and isotopes • Separation of similar elements • Heavier elements placed before lighter ones • Improper arranging of Lanthanides and Actinides
  5. 5. • Meyer (1870)-Arranged elements according to their physical properties. • Elements changed properties gradually in a row or period. • Moseley (1930)- Arrange atoms according to atomic number (nuclear charge). He found a direct correlation between the square root of X-ray energy and nuclear charge (atomic number). Nuclear charge increases by one unit for each element.
  6. 6. •The way the periodic table usually seen isThe way the periodic table usually seen is a compress view, placing the Lanthanidesa compress view, placing the Lanthanides and actinides at the bottom of the stable.and actinides at the bottom of the stable. •The Periodic Table can be arrange by subThe Periodic Table can be arrange by sub shells. The s-block is Group IA and & IIA,shells. The s-block is Group IA and & IIA, the p-block is Group IIIA - VIIIA. The d-the p-block is Group IIIA - VIIIA. The d- block is the transition metals, and the f-block is the transition metals, and the f- block are the Lanthanides and Actinideblock are the Lanthanides and Actinide metalsmetals
  7. 7. •B •2p 1 1 IA 18 VIIIA 1 2 IIA 13 IIIA 14 IVA 15 VA 16 VIA 17 VIIA 2 3 3 IIIB 4 IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB 10 11 IB 12 IIB 4 5 6 7 H 1s1 Li 2s1 Na 3s1 K 4s1 Rb 5s1 Cs 6s1 Fr 7s1 Be 2s2 Mg 3s2 Ca 4s2 Sr 5s2 Ba 6s2 Ra 7s2 Sc 3d1 Ti 3d2 V 3d3 Cr 4s1 3d5 Mn 3d5 Fe 3d6 Co 3d7 Ni 3d8 Zn 3d10 Cu 4s1 3d10 B 2p1 C 2p2 N 2p3 O 2p4 F 2p5 Ne 2p6 He 1s2 Al 3p1 Ga 4p1 In 5p1 Tl 6p1 Si 3p2 Ge 4p2 Sn 5p2 Pb 6p2 P 3p3 As 4p3 Sb 5p3 Bi 6p3 S 3p4 Se 4p4 Te 5p4 Po 6p4 Cl 3p5 Be 4p5 I 5p5 At 6p5 Ar 3p6 Kr 4p6 Xe 5p6 Rn 6p6 Y 4d1 La 5d1 Ac 6d1 Cd 4d10 Hg 5d10 Ag 5s1 4d10 Au 6s1 5d10 Zr 4d2 Hf 5d2 Rf 6d2 Nb 4d3 Ta 5d3 Db 6d3 Mo 5s1 4d5 W 6s1 5d5 Sg 7s1 6d5 Tc 4d5 Re 5d5 Bh 6d5 Ru 4d6 Os 5d6 Hs 6d6 Rh 4d7 Ir 5d7 Mt 6d7 Ni 4d8 Ni 5d8
  8. 8. •Various Elemental Properties change fairly smoothly going across a period or down a group •Properties include: –Atomic and Ionic Radius –Ionization Enthalpy –Electron gain Enthalpy –Electronegativity –Valency
  9. 9. •Atomic Radius:Atomic Radius: •The size of at atomic specie as determine by the boundaries of the valence e-. Largest atomic species are those found in the SW corner since these atoms have the largest n, but the smallest Zeff.
  10. 10. • Cations are always smaller than the original atom. • The entire outer PEL is removed during ionization. • Conversely, anions are always larger than the original atom. • Electrons are added to the outer PEL.
  11. 11. 11p+ Na atom 1 valence electron Valence e- lost in ion formation Effective nuclear charge on remaining electrons increases. Remaining e- are pulled in closer to the nucleus. Ionic size decreases. Result: a smaller sodium cation, Na+
  12. 12. 17p+ Chlorine atom with 7 valence e- One e- is added to the outer shell. Effective nuclear charge is reduced and the e- cloud expands. A chloride ion is produced. It is larger than the original atom.
  13. 13. Ionization enthalpy:Ionization enthalpy: The energy required to remove the valence electron from an atomic specie. Largest toward NE corner of PT since these atoms hold on to their valence e- the tightest.
  14. 14. Electron Affinity:Electron Affinity: The energy release when an electron is added to an atom. Most favorable toward NE corner of PT since these atoms have a great affinity for e-.
  15. 15. • Electronegativity is a measure of an atom’s attraction for another atom’s electrons. • It is an arbitrary scale that ranges from 0 to 4. • The units of electronegativity are Paulings. • Generally, metals are electron givers and have low electronegativities. • Nonmetals are are electron takers and have high electronegativities.