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
- 2. 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.
- 3. • 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.
- 5. • 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.
- 7. 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
- 8. • 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.
- 10. •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
- 12. •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
- 13. •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.
- 14. • 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.
- 15. 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+
- 16. 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.
- 17. 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.
- 18. 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-.
- 19. • 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.