Class 11 chapter 3 Cassification of elements and periodicity in properties ppt

Class 11 chapter 3 classification of elements and periodicity in properties ppt- chemistry

1. CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES

2. Modern periodic law and the present form of the periodic table Modern periodic law states that physical and chemical properties of elements are periodic function of atomic numbers. If the elements are arranged in order of their increasing atomic numbers, the elements with similar properties are repeated after certain regular intervals.

3. Atomic mass depends upon the number of protons and neutrons in the nucleus. The physical and chemical properties could be different depending upon the number of electrons and electronic configuration in any atoms.

4. Cause of periodicity : The properties of elements are repeated after certain regular intervals when these elements are arranged in order of their increasing atomic numbers. The cause of periodicity in properties is the repetition of similar outer electronic configuration.

5. after certain regular intervals. All the alkali metals have the similar outer electronic configuration. All the halogens have similar outer electronic configuration ns 2 np 5 hence possess similar properties. All elements of group 18 have similar electronic configuration ns 2 np 6 and possess similar properties.

6. Long form of periodic table The table which is based upon the electronic configuration of the elements is called the present form or the long form of periodic table. The long form of periodic table consist of 18 vertical columns(groups) and 7 horizontal rows(periods).

7. Nomenclature of elements with atomic number > 100 The naming of the new elements had been traditionally the privilage of the discoverer and the suggested name was ratified by the IUPAC. In recent years this has led to some controversy.

8. Periods in long form of periodic table

9. (i) 1st period (n=1 ; K-shell):- Only 1s orbital is there. It involves only one orbit which can accomodate only two electrons and it have two elements. (ii) 2nd period (n=2 ; L-shell):- Here, one 2s and three 2p orbitals are there. So,total number of orbitals are four and have a capacity of eight electrons. So, second period contains 8 elements. (iii) 3rd period (n=3 ; M-shell):- Here,one 3s, three 3p and five 3d orbitals are there. So, total number of orbitals are nine and have a capacity of eighteen

10. elements. According to Aufbau principle, filling of 3d takes place after 4s. So, effective orbitals are one 3s and three 3p. So, number of orbitals are four and have a capacity of eight elements. (iv) 4th period (n=4 ; N-shell):- Here one 4s, three 4p, five 4d and seven 4f are there. So, total number of orbitals are 16 and have a capacity of 32 elements. According to Aufbau principal, filling of 4d and 4f takes place after 5s. So, effective orbits are one 4s ,five 3d and three 4p. So, number of orbitals are 9 and have a capacity of 18 elements.

11. (v) 5th period(n=5):- Here, one 5s, three 5p, five 5d and seen 5f are there. So, total number of orbitals is 16 and have a capacity of 32 elements. According to Aufbau principa, filling of 5d and 5f takes place after 6p.So, effective orbitals are one 5s, three 5p, five 4d. So,number of orbitals are 9 and have a capacity of 18 elements. (vi) 6th period(n=6):- Here, one 6s, three 6p, five 6d and seven 6f are there.So, total number of orbitals is 16 and have a capacity of 32 elements. According

12. to Aufbau principle, filling of 6d and 6f takes place after 7s. So, effective orbitals are one 6s, seven 4f, five 5d and three 6p. So, number of orbitals are 16 and have a capacity of 32 elements. (vii) 7th period(n=7):- Here,one 7s, three 7p, five 7d and seven 7f are there. So, total number of orbitals are 16 and have a capacity of 32 elements.According to Aufbau principle, filling of 7d and 7f takes place only after 8s.So, effective orbitals are one 7s, seven 5f, five 6d and three 7p. So, number of orbitals are 16 and have a capacity of 32 elements.

13. Groups in long form of periodic table

14. (i)Group 1:- In Group 1, elements except hydrogen is known as Alkali metals because their oxides dissolve in water strong alkalis are obtained. The elements except hydrogen in group 1 are lithium, sodium, potassium, rubidium, caesium, francium, (ii) Group 2:- In Group 2,elements are known as Alkaline Earth metals because their oxides dissolve in water gives their hydroxides and are found on the earth crust.They are also known as S 2 elements because there second subshell contains two

15. electrons. The element in Group 2 are beryllium, magnesium, calcium, strontium, barrium, radium. (iii) Group 3 - Group 12 :- The elements from Group 3 to Group 12 are known as Transition elements because they show transition from highly reactive metals to highly reactive non-metals. (iv) Group 13 :- The elements of Group 13 are known as Boron family. The elements in Group 13 are boron, aluminium, gallium, indium, thallium, nihonium. (v) Group 14 :- The elements in group 14 are carbon,

16. (v) Group 14:- The elements in Group 14 are carbon, silicon, germanium, tin, lead, flerovium. (vi) Group 15 :- The elements in Group 15 are nitrogen, phosphorous, arsenic, antimony, bismuth, moscovium. (vii) Group 16 :- In Group 16, the elements are known as chalcogens it means ore forming. The elements in Group 16 are oxygen, sulphur, selenium, tellurium, polonium, livermorium.

17. polonium, livermorium. (viii) Group 17:- The elements in group 17 are called as halogens.The elements in Group 17 are Flourine, Chlorine, bromine, iodine, astatin, tennessine. (ix) Group 18 :- In Group 18, the elements are known as noble gas. They are also known as inert gases because they does not take part in chemical reaction. Inert means lazy. The elements in Group 18 are helium,neon, argon, krypton, xenon, radon, oganesson.

18. Blocks in long form of periodic table

19. (i) S-block elements:- ‘S’ block contains the elements in Group I and Characteristics:- General electronic configuration ns 1-2 . This block contains all metals. They are soft and have low melting and boiling point. Ionisational enthalpy is less so they are highly reactive because they are not found in nature in free state. They are electropositive.

20. 3. (ii) P-block elements:- ‘P’block contains the elements in Group 13 to Group 18. Charactristics:- General electronic configuration is ns 2 np 1-6 . This block contains metals, non- metals as well as metalloids. They possess high ionisational enthalpy and electron gain enthalpy as compared to s block elements.

21. (iii) D-block elements :- ‘D’block elements contains the elements in Group 3 to Group 12 i.e., the transition elements. Characteristics:- General electronic configuration is (n-1)d 1-10 ns 2 . They all are metals. They possess high melting and boiling point. Most of them are coloured compounds. They exhibit variable valency and variable oxidation number.

22. They are paramagnetic in nature. Most of them acts as catalyst.

23. (iv) F-block elements:- Inner transition elements(Lanthanoids and Actinoids) Characteristics:- General electronic configuration is (n-2)f 1-10 (n-1)d 0-1 ns 2 . They all are metals. They have high melting and boiling point. Most of them are coloured compounds.

24. They exhibit variable valency and variable oxidation numbers. Elements after Uranium are artificially prepared they are called transe uranic elements.

25. PERIODIC TRENDS IN PHYSICAL PROPERTIES

26. I. Atomic Radii:- The distance from the centre of the nucleus to the outermost shell containing electrons. Types of Atomic Radii: (i) Covalent Radius (ii) Metallic Radius (iii) Van der Waal’s Radius

27. (i) Covalent radius:- It is the half of the inter nuclear distance between two covalently bonded atoms of same element in a molecule. (ii) Metallic radius:- It is the half of the inter nuclear distance between two neighbhouring atoms of a metal of the metal latite. (iii) Van der Waal’s radius:- It is the half of the inter nuclear distance between two adjacent atoms of a substance in solid state.

28. Van der Waal’s radius > metallic radius > covalent radius

29. Variation of Atomic radius in period Size of atom decreses when moving from left to right (number of shells remain same). It is because within the period the outer electrons are in the same valence shell and the effective nuclear charge increases as the atomic number increases resulting in the increased attraction of electrons to the nucleus.

30. Variation of Atomic radius in group The atomic radius of elements increases with increase in atomic numbers as we move from top to bottom in a group. As we move down the group the principal quantum number increases.A new energy shell is added at each succeeding elements and valence electrons lie farther and farther away from the nucleus.As a result the attraction of the nucleus for the electron decreses and hence the atomic radius increases.

31. II. Ionic Radius:- The removal of an electron from an atom results in the formation of a cation, whereas gain of an electron leads to an anion. The ionic radius can be estimated by measuring the distances between cations and anions in ionic crystals. The effective distance from the centre of the nucleus of an atom upto which it has an influence in the ionic bond. Species having same number of electrons are called isoelectronic species.

32. Eg:- N 2- , O 2- , F 1- , Ne, Na 1+ , Mg 2+ , Al 3+ have same number of electron i.e., 10. A cation is smaller than its parent atom because it has fewer electrons while its nuclear charge remains the same. The size of an anion will be larger than the parent atom because of the addition of one or more

33. el ectrons. The ionic radii of element exhibit the same trend as the atomic radii. As, nuclear charge increases, the force of attraction by the nucleus on the electrons also increases. As a result ionic radii decreses.

34. III. Ionisational Enthalpy:- The minimum amount of energy required to remove an electron from an isolated gaseous atom at ground state. The unit of ionisational enthalpy is kj/mol. It is represented by ΔH. The energy required to remove the most loosely bound electrons from the isolated gaseous atom is called its first ionisational enthalpy and is denoted by ΔH 1 . The energies required to knock out second

35. and third electrons are called second and third ionisational energies. When one eletron have been removed from the neutral gaseous atom and the positively charged ions formed has one electron less than the number of protons in the nucleus.As a result the electrostatic attraction between the nucleus and the remaining electrons in the cation increases.The positive ion holds its remaining electrons more firmly.Therfore, the energy required to remove another electron from

36. This positively charged ions or second electron from the neutral atom must be higher than the first.

37. Variation of Ionisational Enthalpy in Period The value of ionisational enthalpy increases from left to right with breaks where the atom have somewhat stable configurations. The observed trends can easily be explained on the basis of increased nuclear charge and decreased atomic radii. Both the factors increase the force of attraction towards nucleus and consequently, more and more energy is required to remove the electron and hence, ionisational enthalpy increases.

38. Variations of Ionisational Enthalpy in Groups On moving the group, atomic size increases gradually due to an addition of one new principal energy shell at each succeeding element. On account of this, the force of attraction towards valence electron decreases hence, ionisational enthalpy decreases.

39. Factors affecting ionisational enthalpy:- Atomic size Nuclear charge Shielding effect Electronic configuration

40. IV. Electron gain Enthalpy:- It is defined as the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative ion. It is denoted by ΔH eg . It is measured in electron volts per atom or kj per mole.The process of adding an electron to the atom can be either exothermic or endothermic.

41. Variation of Electron Gain Enthalpy in Periods Electron gain enthalpy becomes more and more negative from left to right in a period. This is due to increase in size and decrease in nuclear charge as the atomic number increases in a period. Both these factors favour the addition of an extra electron due to higher force of attraction by the nucleus for the incoming electron.

42. Variation of Electron Gain Enthalpy in Groups The electron gain enthalpies, in general, become less negative in going from top to bottom in a group. This is due to increase in size on moving down a group. This factor is predominant in comparison to other factors, i.e., increase in nuclear charge.

43. V. Electronegativity:- It is the tendancy of an atom to attract the shared pair of electrons more towards itself in a covalent bond. It is not a measurable property. It is directly related to non-metallic property of an element because they have greater tendancy to gain electrons. It is inversely proportional to metallic characters. It increase when moving across the period and decreases when moving down the group. Pauling scale is used to measure electronegativity.

44. PERIODIC TRENDS IN CHEMICAL PROPERTIES

45. Periodicity of valence or oxidation states The electrons present in the outermost shell of an atom are called valence electrons and the number of these electrons determine the valency of the atom.

46. Variation along a period As we move across from left to right, the number of electrons increases from 1 to 8. But the valence of elements , H or O first increases from 1 to 4 and then decreases to 0. In the formation of Na 2 O molecule, oxygen being more electronegative accepts two electrons one from each of the two sodium atoms and thus shows an oxidation state of -2. On the other hand sodium with valence electronic configuration 3s 1 loses one electron to oxygen and is

47. give an oxidation state of +1. Thus, the oxidation state of an element in a given compound may be defined as the charge acquired by its atom on the basis of electronegativity of the other atom in the molecule.

48. Variation within a Group When we move down the group, the number of valence electrons remains the same, therefore, all the elements in a group exhibit the same valency.

49. Anomalous property of second period elements It has been observed that some elements of second period show similarities with the elements of the third period placed diagonally to each other though, belonging to different groups. The similarity in properties of elements placed diagonally to each other is called diagonal relationship.

50. The anomalous behaviour is due to their small size; large charge and high electronegativity of elements. In addition, the first member of group has only four valence orbitals available for bonding, while the second member of group has nine valence orbitals.As a consequence of this, the maximum covalency of first member of each group is 4, whereas the other members of the group can expand their valence shell to accomodate more than four pairs of electrons.

51. Periodic trends and Chemical Reactivity METALS:- The reactivity of metals is measured in terms of their tendancy to lose electron from their outermost shell. In a period the tendancy of element to lose electrons decreases in going from left to right. So, the reactivity of metals decreases in a period from left to right.

52. In a group the tendancy of element to lose e lectron increases as we go down. So, the reactivity of metals increases down the group. NON-METALS:- The reactivity of a non-metal is measured in terms of its tendancy to gain electrons to form an anion. In a period the reactivity of non-metals increases from left to right.During reactions,

53. non-metals tend to form anions. In a group the reactivity of non-metals decreases as we go down.This is because the tendancy to accept electrons decreases down the group.

54. Thank you... Presented by: A.P.Devanampriya