CLASSIFICATION OF ELEMENTS & PERIODICITY IN PROPERTIES.pptx

Development of periodic table

1. CLASSIFICATION OF ELEMENTS & PERIODICITY IN PROPERTIES

2. PERIODICITY R epeatation in properties.

3. WHY DO WE NEED TO CLASSIFY ELEMENTS ? In 1800 – 31 element discovered In 1865 – 63 elements At present – > 114 elements (118)

4. PERIODIC TABLE Arrangement of elements with similar properties placed together Result of experimental observation

5. DEVELOPMENT OF PERIODIC TABLE

6. LAVOISIER CLASSIFICATION 1789 French chemist & biologist Father of chemistry Classify element based on their physical properties Classify elements into metals & non-metals.

7. DRAWBACKS Metalloids As the number of element increases, this classification become insufficient for study of elements.

8. DOBERNIER’S TRIADS (1829) F irst classification of elements in group Each group contain three elements of similar properties If these three elements are arranged in increasing order of their atomic weight, then the atomic mass of middle element will be the average rest two. These elements are arranged in increasing order of their atomic mass such that the atomic weight of the middle element was the arithmetic mean of other two . or

9. 7 Li 23 Na 39 K 7 + 39 /2 = 46/2 = 23 1 H 19 F 35.5 Cl 36.5/2 = 19 Ex – (Be, Mg, Ca ), (K, Rb , Cs)

10. DE CHAN COURTOIS’S TELLURIC HELIX MODEL: - ( 1862) French geologist Telluric helix/screw model Based on the atomic weight (increasing order) Cylindrical table of elements. Did not attract so much attention.

11. NEWLAND’S OCTAVE LAW : - (IN 1865) In 1865 – according to NCERT In 1864 – exact British chemist Arrangement of elements in order of their increasing atomic mass. Every 8 th element node of an octave of music.(musical notes).

12. 1 Sa 2 Re 3 Ga 4 Ma 5 Pa 6 Dha 7 Ni Li Be B C N O F Na Mg Al Si P S Cl K Ca (failed)

13. DRAWBACKS : - Valid only upto calcium, after that 18 th element had similar properties Failure of octave, after the discovery of inert gas (?). Inert gas discovered after Mandeleve won.

14. LOTHER MAYER’S CURVE : - (IN 1868) German chemist Arrangement of elements over graph paper in increasing atomic weight w.r.t physical properties like atomic volume, Melting point & boiling point, etc.

15. CONCLUSION : - Elements having similar properties occupies similar position in graph At the tip – alkali metal At descending line – halogen Valley of the graph – high melting non – metals, metalloids, transition metals. Resembles with the modern periodic table.

16. MENDELEEV’S PERIODIC TABLE : - Russian chemist Arrangement of elements in order of increasing atomic weight First successful classification in the form of periodic table . Based on periodic law Physical & chemical properties of elements are the periodic function of their atomic weight

17. PERIODIC TABLE Horizontal rows Period - 7 Vertical column Group 8 in Mendeleev original table 9 th group c/a inert gases/zero group added later. Each group divided into sub groups Group I to VII – 2 subgroup - A & B Group VIIII – 3 subngroup – A, B, & C

18. MAIN FEATURES OF MENDEELEV PERIODIC TABLE IA – alkali metal ( strong base/water soluble base) IB – coinage metals ( very less reactive ,; Cu ; Ag; Au ) IIA – alkaline earth metals (strong base, water ,soluble , found in soil; except Be , Mg ) IIB – low boiling metals (except – Zn, Cd, Hg) VA – pnicogen (fertilizers/poisons/explosive foarmers ) VIA – chalcogen ( ore forming ) VII A – halogen (sea salt formers) Zero group – inert gas / noble gas( non- reactive gas).

19. Prediction of unknown/undiscovered elements; for this Mandeleev left several gaps. EX – Ga Sc Ge Tc These elements were discovered at that time Mandeleev left space for all these elements Use ‘EKA’ word for Gap

20. Eka Al -  Ga Eka B  Sc Eka Si  Ge Eka Mn  Tc First artificial element of periodic table Correction of atomic weight of some elements Eg – Be  13.5 (before)  9 (after mandeleev )

21. DIFFERENT RELATIONSHIPS Diagonal relationships Bridge relationships

22. Diagonal relationships Bacause of similar properties like ionic size,, ionic potential , E.N. etc Shown by metals & ,metalloids of 2 nd & 3 rd period of ~A subgroup. 2 nd - Li Be B C N 3 rd – Na Mg Al , Si, P

23. Bridge relationship Li Be B C Na Mg Al Si i.e. properties of Li is similar to Na & Mg thus forms a triad Thus Li is bridge head element Bridge triad (Ag, Ca , Zn) (Be, Ca , Zn) (Mg, Sr , Cd)

24. Demarits of Mandeleev’s periodic table - Position of hydrogen Position/place of isotopes (same atomic number but different atomic mass) Placement of some elements against periodic law (based on increasing atomic weight) i.e. some elements having higher atomic weight than next one, placed before.

25. Ex – Ar 40 K 39 Te 127 I 126 Th 232 Pa 231 Co 59 Ni 58.9 Grouping of similar elements Ex – Cu & Ag (don’t have similar properties with alkali metals) Separation of similar elements Au & P(both have similar properties but present in different group).