1. The Periodic Classification of Elements

2. EARLIER ATTEMPTS OF CLASSIFICATION OF ELEMENTS The first classification of elements was as metals and non-metals. This served only limited purpose mainly because of two reasons: 1. All the elements were grouped in to these two 2. Some elements showed properties of both-metals and non-metals and they could not be placed in any of the two classes. classes only. Moreover the group containing metals was very big.

3. 1825 1835 1845 1855 1865 1875 1885 1895 1905 1915 1925 In 1864 John Alexander Newland, an English chemist, arranged in the increasing order of their atomic masses* every eighth element had properties similar to the first element. 1869 Dmitry Mendeleev** a Russian chemist while trying to classify elements discovered that on arranging in the increasing order of atomic mass*, elements with similar chemical properties occurred periodically. Henry Moseley, an English physicist discovered in the year 1913 that atomic number, is the most fundamental property of an element and not its atomic mass. In 1829, Dobereiner, a German scientist made some groups of three elements each and called them triads In 1870, Meyer unaware of Mendeleev’s study has also been working on his periodic table consisting of 56 elements. His work involved the discovery of transuraniu m elements 94 to 102.

4. Johan Dobereiner 1871. Johan Dobereiner grouped elements with similar properties during 1817 to 1829. He, through his work saw some pattern in threes. 1871. Johan Dobereiner grouped elements with similar properties during 1817 to 1829. He, through his work saw some pattern in threes. The halogens chlorine, bromine, and iodine possessed similar properties as well as the alkali metals sodium, lithium, and potassium. The halogens chlorine, bromine, and iodine possessed similar properties as well as the alkali metals sodium, lithium, and potassium. His idea of 'triads' led others to look at the same idea. His idea of 'triads' led others to look at the same idea.

5. A. E. Beguyer de Chancourtois When Dobereiner chose to look at the properties of elements, 1862 A. E. Beguyer de Chancourtois chose the atomic weights. When Dobereiner chose to look at the properties of elements, 1862 A. E. Beguyer de Chancourtois chose the atomic weights. His method used the idea of writing the elements down in a continuous and uniformly spaced interval list. His method used the idea of writing the elements down in a continuous and uniformly spaced interval list.

6. John Newland In 1863 John Newland’s viewed the arrangement as best being presented in what he called the Law of Octaves. In 1863 John Newland’s viewed the arrangement as best being presented in what he called the Law of Octaves. It was much like the triads but utilized the atomic weights. It was much like the triads but utilized the atomic weights. He noted that the elements would repeat their chemical properties every eighth element. He noted that the elements would repeat their chemical properties every eighth element. This was later found to be a very useful idea when working with the arrangement of the elements. This was later found to be a very useful idea when working with the arrangement of the elements.

7. Dmitri Ivanovich Mendeleev In 1869, Mendeleev discovered that the atomic weights of elements were related to the periodic variation in their properties. In 1869, Mendeleev discovered that the atomic weights of elements were related to the periodic variation in their properties. He arranged the elements He arranged the elements according to increasing atomic weights providing intervals or periods w/c were not always of the same length. according to increasing atomic weights providing intervals or periods w/c were not always of the same length. This intervals showed a change in properties of the elements from the first to the last element of the table. This intervals showed a change in properties of the elements from the first to the last element of the table.

8. Lothar Meyer In 1870, Meyer unaware of Mendeleev’s study has also been working on his periodic table consisting of 56 elements. In 1870, Meyer unaware of Mendeleev’s study has also been working on his periodic table consisting of 56 elements. He also maintained that the properties of the elements are periodic functions of their atomic mass. He also maintained that the properties of the elements are periodic functions of their atomic mass.

9. Dmitri Ivanovich Mendeleev and Lothar Meyer Two people, working independently, came up with what is today considered our working model for the periodic table of the elements. Two people, working independently, came up with what is today considered our working model for the periodic table of the elements. Mendeleev published his work in 1869 while Meyer did the same in 1870. Because Mendeleev's work was published first he is usually recognized as the father of the periodic table Mendeleev published his work in 1869 while Meyer did the same in 1870. Because Mendeleev's work was published first he is usually recognized as the father of the periodic table Dmitri Ivanovich Mendeleev and Lothar Meyer worked on the idea of atomic weights.

10. Henry G. J. Moseley 1894. The work of H. G. J. Moseley brought the elements in to a new arrangement (although minimal). 1894. The work of H. G. J. Moseley brought the elements in to a new arrangement (although minimal). He selected to arrange the elements by their atomic number (number of protons) rather than their weight. His work in 1914 led to what we call the Law of Chemical Periodicity. He selected to arrange the elements by their atomic number (number of protons) rather than their weight. His work in 1914 led to what we call the Law of Chemical Periodicity.

11. Henry G. J. Moseley Periodic Law states that: the physical and chemical properties of elements are a periodic function of atomic number. Periodic Law states that: the physical and chemical properties of elements are a periodic function of atomic number.

12. Glenn Seaborg Finishing out this illustrious group of people is Glenn Seaborg. Finishing out this illustrious group of people is Glenn Seaborg. His work involved the discovery of transuranium elements 94 to 102. His work involved the discovery of transuranium elements 94 to 102. This work led to the addition of the lanthanides and actinides (lathanoids and actinoids) [some say actinoins and lathanoins] in the periodic table. He and his colleagues are credited with discovering over 100 isotopes. This work led to the addition of the lanthanides and actinides (lathanoids and actinoids) [some say actinoins and lathanoins] in the periodic table. He and his colleagues are credited with discovering over 100 isotopes.

13. From those works the Periodic Table emerged.

14. Period The horizontal rows in the PT are known as PERIOD or SERIES. The first period is the shortest period of all and contains only 2 elements, H and He. The second and third periods are called short periods and contain 8 elements each.

15. Fourth and fifth periods are long periods and contain 18 elements each. Sixth and seventh periods are very long periods containing 32 elements* * each.

16. Period The sixth series is called Lanthanide series The sixth series is called Lanthanide series And the last is called the Actinide series And the last is called the Actinide series

17. Group A group, also known as a family, is a vertical column in the periodic table of the chemical elements. There are 18 groups in the standard periodic table. A group, also known as a family, is a vertical column in the periodic table of the chemical elements. There are 18 groups in the standard periodic table. The letters A and B were designated to main group elements (A) and transition elements (B). The letters A and B were designated to main group elements (A) and transition elements (B).

18. Group The stairway that starts from Boron separates metals from the non metals. The stairway that starts from Boron separates metals from the non metals. About 20 elements are nonmetals and these are found above and to the right of the stairway. About 20 elements are nonmetals and these are found above and to the right of the stairway. Element found along the stairway are the so called Metalloids Element found along the stairway are the so called Metalloids

19. Group The modern explanation of the pattern of the periodic table is that the elements in a group have similar configurations of the outermost electron shells of their atoms: as most chemical properties are dominated by the orbital location of the outermost electron The modern explanation of the pattern of the periodic table is that the elements in a group have similar configurations of the outermost electron shells of their atoms: as most chemical properties are dominated by the orbital location of the outermost electron

20. Group 1 Group 17 All elements of group 1 have only one valence electron. Li has electrons in two shells, Na in three, K in four while Rb has electrons in five shells. Similarly all the elements of group 17 have seven valence electrons however the number of shells is increasing from two in F to five in I. ElementElectronic configurationElementElectronic configuration Li2,1F2,7 Na2,8,1Cl2,8,7 K2,8,8,1Br2,8,8,7 Rb2,8,8,8,1I2,8,18,8,7

21. The gradual filing of the third shell can be seen below. Element NaMgAlSiPSClAr Electronic configur ation 2,8,12,8,22,8,32,8,42,8,52,8,62,8,72,8,8

22. PERIODIC PROPERTIES We have also learned that in a period the number of valence electrons and the nuclear charge increases from left to right. It increases the force of attraction between them. In a group the number of filled shells increases and valence electrons are present in higher shells. This decreases the force of attraction between them and the nucleus of the atom. These changes affect various properties of elements and they show gradual variation in a group and in a period and they repeat themselves after a certain interval of atomic number. Such properties are called periodic properties.

23. Periodic Properties and their Variation in the Periodic Table Valency in a period : the number of valence electrons increases in a period. In normal elements it increases from 1 to 8 in a period from left to right. It reaches 8 in group 18 elements (noble gases) which show practically no chemical activity under ordinary conditions and their valency is taken as zero.

24. Atomic radii A number of physical properties like density and melting and boiling points are related to the sizes of atoms. Atomic size is difficult to define. Atomic radius determines the size of an atom. For an isolated atom it may be taken as the distance between the centre of atom and the outermost shell.

25. Practically, measurement of size of an isolated atom is difficult; therefore, it is measured when an atom is in company of another atom of same element. Atomic radii is defined as one-half the distance between the nuclei of two atoms when they are linked to each other by a single covalent bond. Atomic radii

26. Variation of atomic radii in a period Atomic radii of 2nd and 3rd period elements are given in the table below. What do you observe? In a period, atomic radius generally decreases righ t. 2nd Period Li Be B C N O F 155 112 98 91 92 73 72 3rd Period Na Mg Al SiPS Cl 190 160 143132 128 127 99 Can you explain this trend? You have learnt in the beginning of this section that in a period there is a gradual increase in the nuclear charge. Since valence electrons are added in the same shell, they are more and more strongly attracted towards nucleus. This gradually decreases atomic radii.

27. Variation of atomic radii in a group What happens to atomic radii in a group? Atomic radii increase in a group from top to bottom.

28. Ionic radii Ionic radius is the radius of an ion. On converting into an ion the size of a neutral atom changes. Anion is bigger than the neutral atom. This is because addition of one or more electrons increases repulsions among electrons and they move away from each other.

29. On the other hand a cation is smaller than the neutral atom. When one or more electrons are removed, the repulsive force between the remaining electrons decreases and they come a little closer. Ionic radii

30. Variation of ionic radii in periods and groups Ionic radii show variations similar to those of atomic radii. Thus, ionic radii increase in a group. Ionic radii decrease in a period.

31. Ionization energy Negatively charged electrons in an atom are attracted by the positively charged nucleus. For removing an electron this attractive force must be overcome by spending some energy. The minimum amount of energy required to remove an electron from a gaseous atom in its round state to form a gaseous ion is called ionization energy.

32. Variation of ionization energy in a group and period We have already seen earlier, that the force of attraction between valence electrons and nucleus decreases in a group from top to bottom. What should happen to their ionization energy values? Ionization energy decreases in a group from top to bottom. The ionization energy increases in a period from left to right.

33. Electron affinity Another important property that determines the chemical properties of an element is the tendency to gain an additional electron. This ability is measured by electron affinity. It is the energy change when an electron is accepted by an atom in the gaseous state. By convention, electron affinity is assigned a positive value when energy is released during the process. The greater value of electron affinity, means more energy is released during the process and greater is the tendency of the atom to gain electron.

34. Variation of electron affinity in a group & period In a group, the electron affinity decreases on moving from top to bottom, that is, less and less amount of energy is released. In a period, the electron affinity increases from left to right, that is, more and more amount of energy is released.

35. Electronegativity Electronegativity is relative tendency of a bonded atom to attract the bond- electrons towards itself. Electronegativity is a dimensionless quantity and does not have any units. It just compares the tendency of various elements to attract the bond-electrons towards themselves.

36. Variation of electronegativity in a group & period Electronegativity decreases in a group from top to bottom. Electronegativity increases in a period from left to right.

37. Metallic and non-metallic character You know what are characteristic properties of a metal? They are its electropositive character (the tendency to lose electrons), metallic luster, ductility, malleability and electrical conductance. Metallic character of an element largely depends upon its ionization energy. Smaller the value of ionization energy, more electropositive and hence more metallic the element would be.

38. Variation of metallic character in a group & period Metallic character of elements increases in a group from top to bottom. Metallic character of elements decreases in a period from left to right

39. Summary Atomic radii Defined as one-half the distance between the nuclei of two atoms when they are linked to each other by a single covalent bond. Ionic size The radius of an ion. On converting into an ion the size of a neutral atom changes. Metallic Property They are its electropositive character (the tendency to lose electrons), metallic luster, ductility, malleability and electrical conductance.

40. Summary Ionization Energy The minimum amount of energy required to remove an electron from a gaseous atom in its round state to form a gaseous ion Electron Affinity The tendency of an atom to gain an additional electron Ionization Energy The relative tendency of a bonded atom to attract the bond-electrons towards itself.

41. Summary VariationGroup Top to Bottom Period Left to Right Atomic sizeIncreasingDecreasing IonizationDecreasingIncreasing Electron AffinityDecreasingIncreasing ElectronegativityDecreasingIncreasing Metallic PropertyIncreasingDecreasing

42. ACTIVITY 1 Arrange the elements Li, Al, B, and Br in order of Arrange the elements Li, Al, B, and Br in order of –A. increasing atomic size –B. decreasing ionization energy –C. increasing electronegativity

43. ACTIVITY 2 Choose which is the larger member of each pair: Choose which is the larger member of each pair:

44. ACTIVITY 3 Given the hypothetical elements: Given the hypothetical elements: Determine the group and series where each element will be found in the PT. Determine the group and series where each element will be found in the PT.

45. ACTIVITY 4 Select which is the Select which is the – smallest atom –Biggest atom –atom that would require the greatest ionization energy –Most electronegative –Noble gas –nonmetal

46. Group → 123456789101112131415161718 ↓ Period 1 H 1.0 08 He 4.00 3 2 Li 6.9 41 Be 9.01 2 B 10.8 1 C 12.0 1 N 14.0 1 O 16.0 0 F 19.0 0 Ne 20.1 8 3 Na 22. 99 Mg 24.3 1 Al 26.9 8 Si 28.0 9 P 30.9 7 S 32.0 7 Cl 35.4 5 Ar 39.9 5 4 K 39. 10 Ca 40.0 8 Sc 44.9 6 Ti 47.8 7 V 50.9 4 Cr 52.0 0 Mn 54.9 4 Fe 55.8 4 Co 58.9 3 Ni 58.6 9 Cu 63.5 5 Zn 65.3 9 Ga 69.7 2 Ge 72.6 1 As 74.9 2 Se 78.9 6 Br 79.9 0 Kr 83.8 0 5 Rb 85. 47 Sr 87.6 2 Y 88.9 1 Zr 91.2 2 Nb 92.9 1 Mo 95.9 4 Tc [98] Ru 101. 07 Rh 102. 91 Pd 106. 42 Ag 107. 87 Cd 112. 41 In 114. 82 Sn 118. 71 Sb 121. 76 Te 127. 60 I 126. 90 Xe 131. 29 6 Cs 13 2.9 1 Ba 137. 33 * Hf 178. 49 Ta 180. 95 W 183. 84 Re 186. 21 Os 190. 23 Ir 192. 22 Pt 195. 08 Au 196. 97 Hg 200. 59 Tl 204. 38 Pb 207. 2 Bi 208. 98 Po [209 ] At [210 ] Rn [222 ] 7 Fr [22 3] Ra [226 ] ** Rf [263 ] Db [262 ] Sg [266 ] Bh [264 ] Hs [269 ] Mt [268 ] Ds [272 ] Rg [272 ] Uub [277 ] Uut [284 ] Uuq [289 ] Uup [288 ] Uuh [292 ] Uus [291 ]‡ Uuo [293 ]‡ Lanthanides La 138. 91 Ce 140. 12 Pr 140. 91 Nd 144. 24 Pm [145 ] Sm 150. 36 Eu 151. 96 Gd 157. 25 Tb 158. 93 Dy 162. 50 Ho 164. 93 Er 167. 26 Tm 168. 93 Yb 173. 04 Lu 174. 97 ** Actinides Ac [227 ] Th 232. 04 Pa 231. 04 U 238. 03 Np [237 ] Pu [244 ] Am [243 ] Cm [247 ] Bk [247 ] Cf [251 ] Es [252 ] Fm [257 ] Md [258 ] No [259 ] Lr [262 ]

47. Thank you for listening! End of Presentation! End of Presentation! Exam next meeting. Exam next meeting.