Structure of Atom

Structure of Atom

1. Lesson plan Class- 9 th Subject-Science TOPIC:-Atomic structure

2. 1] … GENERAL OBJECTIVE. 2] … SPECIFIC OBJECTIVE. 3] … P.K. TESTING. 4] … ANNOUNCEMENT OF TOPIC. 5] … MOTIVATION. 6] … PRESENTATION. 7] … GROUP ACTIVITY. 8] … EVALUATION. 9] … HOME ASSIGNMENT. CONTENTS

3. GENERAL OBJECTIVES To develop the interest and scientific attitude among the students. To develope the abilities like sensing the problem organise and interpret analyse and generalize discuss and argue 3. To develop critical attitude

4. SPECIFIC OBJECTIVES Students recognize electrical charge in matters  Describe in detail theme and content of activity. Student recognizes Thompson model of atom.  Students recognizes that: Most alpha particles are un-deflected Few alpha particles are slightly deflected Few alpha particles bounce back Students recognize Nucleus and orbits They explain the defects of Rutherford’s Model of Atom Students recognize motion of electron in orbits around nucleus of an atom Students explain about the distribution of electrons in different energy levels Students recognizes 1. Elements and their symbols 2. atomic number 3.No. of protons, electrons and neutrons 4.. distributions of electrons in shells 5.. valency of atoms Students recognizes atomic and mass number Students recognizes isotopes Students recognize isobars

5. PREVIOUS KNOWLEDGE TESTING See the picture and tell what is the building unit in this picture Ans :- brick

6. In piece of chalk, what are its constituent partical ? Ans :- Molecule

7. In piece of gold, do you know what are its constituent partical ? Ans :- Atom

8. Do you know, who gave the word atom? Ans :- No Democritus gave the word Atoma in 460 BC. What is the meaning of Atoma ? Ans :- Its Greek word meaning Indivisible. Democritus

9. Do you know the atoms of an element are same? Yes, Atoms of an element are same. Do you know the atoms of different elements are different? Yes, Atoms of different elements are different. In what respect these atoms differ from one another? Atoms differ in terms of structure from one another. Element silver Element platinum Element gold

10. What may be the structure of atom, do you know? Ans :- No

11. Motivation As the building is made up of bricks, chalk is made up of molecules, gold is made up of atoms and gold and iron have different atoms, they differ in respect of their structure. Now we should be familiar with the STRUCTURE OF AN ATOM.

12. Announcement of the Topic Well students today we will discuss and develop the idea of STRUCTURE OF AN ATOM

13. Do you recognize the person in this picture? Ans :- No He is John Dalton. Who gave the indivisible nature of the atom? Ans :- John Dalton in 1808 gave the idea of indivisibility of an atom. John Dalton John Dalton

14. Comb dry hair Comb from hair pieces of paper Attraction If comb is taken near the pieces of paper what will happen? Ans :- ATTRACTION

15. Why this attraction takes place? glass rod with a silk cloth inflated balloon . attraction If this rod is taken near the balloon then what will happen?

16. CHARGED NATURE OF THE PARTICLES Where does this charge come from? Ans :- An atom is divisible and consists of charged particles. Opposite charges attracts each other and same charges repel each other .

17. By the end of 19 th century, scientists came to know that atom is not indivisible but divisible and consist of sub-atomic particles namely ELECTRON, PROTON and NEUTRON , the fundamental particles. Who has discovered electron? Ans :- J.J. Thomson. Joseph John Thomson

18. Who has discovered proton? Ans :- E. Goldstein Who has discovered neutron? Ans :- J. Chadwick James Chadwick Emanual Goldstein

19. Now next problem before the scientist was to explore the positions of these sub-atomic particles in the atom So, first attempt was made by J.J. Thompson to arrange these sub-atomic particles by giving PLUM PUDDING MODEL

20. See the picture and describe it. Thomson proposed that: An atom consists of a positively charged sphere and the electrons are embedded in it. (ii) The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral.

21. According to J.J. Thompson whether is electrically neutral or not? Ans :- Yes, electrically neutral. How are the electrons arranged within an atom and name the scientist who gave this arrangement? Ans :- Rutherford gave the arrangement of electrons within the atom by performing his α -particle scattering experiment

22. Rutherford ‘Scattering’ Lead collimator Gold foil particle source a q

23. Rutherford’s Apparatus beam of alpha particles

24. Rutherford’s Apparatus Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3 rd Edition, 1990, page 120 beam of alpha particles radioactive substance fluorescent screen circular - ZnS coated gold foil

25. Lead block Polonium Gold Foil Florescent Screen

26. What he expected …

27. Because he thought the mass was evenly distributed in the atom. - - - - -

28. Because, he thought the mass was evenly distributed in the atom - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

29. What he got…

30. Interpreting the Observed Deflections . . . . . . . . . . . . . . gold foil deflected particle undeflected particles . . beam of alpha particles .

31. The observations : (1) Most of the alpha particles pass through the foil un-deflected. (2) Some alpha particles are deflected slightly as the penetrate the foil. (3) A few (about 1 in 20,000) are greatly deflected. (4) A similar small number do not penetrate the foil at all, but are reflected back toward the source. Rutherford believed that when positively charged alpha particles passed near the positively charged nucleus, the resulting strong repulsion caused them to be deflected at extreme angles. Rutherford's interpretation : If atoms of the foil have a massive, positively charged nucleus and light electrons outside the nucleus, one can explain how: (1) an alpha particle passes through the atom un-deflected (a fate share by most of the alpha particles); (2) an alpha particle is deflected slightly as it passes near an electron; (3) an alpha particle is strongly deflected by passing close to the atomic nucleus; and (4) an alpha particle bounces back as it approaches the nucleus head-on.

32. Rutherford Scattering (cont.) Rutherford interpreted this result by suggesting that the a particles interacted with very small and heavy particles Particle bounces off of atom? Particle attracts to atom? Particle goes through atom? Particle path is altered as it passes through atom? . Case A Case B Case C Case D

33. Explanation of Alpha-Scattering Results Plum-pudding atom + + + + + + + + - - - - - - - - Alpha particles Nuclear atom Nucleus Thomson’s model Rutherford’s model

34. Results of foil experiment if plum-pudding had been correct. Electrons scattered throughout positive charges + + + + + + + + - - - - - - - -

35. Interpreting the Observed Deflections . . . . . . . . . . . . . . gold foil deflected particle undeflected particles . . beam of alpha particles .

36. Rutherford’s Gold-Leaf Experiment Conclusions: Atom is mostly empty space Nucleus has (+) charge Electrons float around nucleus

37. Actual Results of Gold-Leaf Experiment n +

38. The Rutherford Atom n + - - - - - - - - - - On the basis of this picture draw the conclusion

39. On the basis of his experiment, Rutherford put forward the nuclear model of an atom, which had the following features: ( i ) There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus. (ii) The electrons revolve around the nucleus in circular paths. (iii) The size of the nucleus is very small as compared to the size of the atom.

40. Rutherford’s Model of the Atom

41. Bohr Atom The Planetary Model of the Atom

42. What were the Drawbacks of Rutherford’s model of the atom?

43. From classical E&M theory, an accelerated electric charge radiates energy (electromagnetic radiation), which means the total energy must decrease. So the radius r must decrease!! Physics had reached a turning point in 1900 with Planck’s hypothesis of the quantum behavior of radiation, so a radical solution would be considered possible. Electron crashes into the nucleus!?

44. Drawbacks of Rutherford’s model of the atom According to classical physics, light should be emitted as the electron circles the nucleus. A loss of energy would cause the electron to be drawn closer to the nucleus and eventually spiral into it . And atom brust

45. Rutherford’s model of the atom did not explain the stability of atom

46. Do you recognize the person in this picture? Yes , Neils Bohr For what he is recognized? He gave model of atom after the faliure of Rutherford’s model of the atom Neils Bohr (1885-1962 )

47. Electrons in Atoms nucleus (+) electron (-) Explain this picture

48. Bohr’s Model Nucleus Electron Orbit Energy Levels

49. Neils Bohr put forward the following postulates about the model of an atom: ( i ) Only certain special orbits known as discrete orbits of electrons, are allowed inside the atom. These orbits or shells are called energy levels. shells are represented by the letters K,L,M,N ,… or the numbers, 1,2,3,…..

50. BOHR’S MODEL FOR ATOM ii) The energy of an electron in the orbit does not change with time. If electron has to lose or gain energy then what will happen? the electron will move from a lower stationary state to a higher stationary state when required amount of energy is absorbed by the electron or energy is emitted when electron moves from higher stationary state to lower stationary state ΔE = E f – E i The energy change does not take place in a continuous manner.

51. Increasing energy of orbits n = 1 n = 2 n = 3 A photon is emitted with energy E = hf e - e - e - e - e - e - e - e - e - e - e -

52. How are Electrons Distributed in Different Orbits (Shells)? The distribution of electrons into different orbits of an atom was suggested by Bohr and Bury. What are these rules? 1.The maximum number of electrons present in a shell is given by the formula 2n 2 ,where ‘n’ is the orbit number or energy level index, 1,2,3,…. How many number of electrons are present in 1 st orbit i.e. n=1 2 How many number of electrons are present in 1 st orbit i.e. n=2 8 How many number of electrons are present in 1 st orbit i.e. n=3 18

53. Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner.

54. The Atom Helium Electron Proton Neutron Helium has two electrons, two protons and two neutrons

55. The Atom Lithium Protons Neutrons Electrons

56. The Atom Beryllium Protons Neutrons Electrons Beryllium has four electrons, four protons and five neutrons.

57. The Atom Boron Protons Neutrons Electrons Boron has five electrons, five protons and six neutrons.

58. The Atom Carbon Protons Neutrons Electrons Carbon has six electrons, six protons and six neutrons.

59. The Atom Nitrogen Protons Neutrons Electrons Nitrogen has seven electrons, seven protons and seven neutrons.

60. The Atom Oxygen Protons Neutrons Electrons Oxygen has eight electrons, eight protons and eight neutrons.

61. The Atom Fluorine Protons Neutrons Electrons Fluorine has nine electrons, nine protons and ten neutrons.

62. The Atom Neon Protons Neutrons Electrons Neon has ten electrons, ten protons and ten neutrons.

63. The Atom Sodium Protons Neutrons Electrons Sodium has eleven electrons, eleven protons and twelve neutrons.

64. The electrons present in the outermost shell of an atom are known as the valence electrons. + + + + + + + + - - - - - - - - What are the valency electrons in this atom six Do you know what are Valency electrons

65. What is valency ? The number of electrons present in the valency shell or eight minus number of electrons present in the valency shell which is less is known as valency . What is valency of magnesium and aluminium ? 2 and 3 respectively. Why is the valency of oxygen 2 ?

66. Why different elements have different atomic number? Elements are different because they contain different numbers of PROTONS What is atomic number? The “ atomic number ” of an element is the number of protons in the nucleus No of protons in an atom = no of electrons in neutral atom

67. Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. Element No of protons Atomic no (Z) Carbon Phosphorus Gold 6 6 15 79 79 15

68. Mass number is the number of protons and neutrons in the nucleus of an atom What is Mass Number ? Mass no = p + + n

69. Mass Number Mass number is the number of protons and neutrons in the nucleus of an atom: Mass = p + + n Nuclide p + n e - Mass # Oxygen - 8 - 6 6 - 31 15 8 8 16 16 carbon 12 6 12 Phosphorus 15 31 16

70. What is the symbolic representation of elements?

71. Complete Symbols Contain the symbol of the element, the mass number and the atomic number . X Mass number Atomic number Subscript → Superscript →

72. Represent the symbols of nitrogen,carbon and neon If atoms of same element have same no of protons and different no of neutrons then what term is used to represent them? Isotopes

73. Isotopes Atoms of the same element can have different numbers of neutrons . Thus,have different mass numbers. These are called isotopes .

74. Naming Isotopes We can put the mass number after the name of the element: carbon-12 carbon-14 uranium-235

75. Isotopes are atoms of the same element having different masses , due to varying numbers of neutrons. Isotope Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) Hydrogen-2 (deuterium) Hydrogen-3 (tritium) 1 1 1 1 1 1 1 2

76. What are ISOBARS? Atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars Give the examples of isobars 40 S , 40 Cl , 40 Ar , 40 K , and 40 Ca

77. Assignments to various groups: Group 1( J.J. Thomson ) Discuss J.J. Thomson model 1. Write the distribution of electrons in carbon and sodium atoms. 2. If K and L shells of an atom are full, then what would be the total number of electrons in the atom? Group 2( John Dalton ) Discuss John Dalton theory of matter 1. Write the distribution of electrons in magnesium and nitrogen atoms. 2. If 1and 2 shells of an atom are full, then what would be the total number of electrons in the atom? Group 3( Rutherford ) Discuss Rutherford scattering experiment and its model 1. Write the distribution of electrons in oxygen and aluminium atoms. 2. If L and M shells of an atom are full, then what would be the total number of electrons in the atom? Group4( Neils Bohr ) Discuss Bohr’s model of atom. 1. Write the distribution of electrons in silicon and fluorine atoms. 2. If M and N shells of an atom are full, then what would be the total number of electrons in the atom?

78. Presentation by the various groups

79. EVALUATION How dose matter aquire charge? According Thompson model of atom how  the atom is electrically neutral. Most alpha particles are un-deflected in ruther ford scattering experiment why? Few alpha particles are slightly deflected why? Few alpha particles bounce back why? What is orbits? What are defects of Rutherford’s Model of Atom? How are electrons distributed in different energy levels of atom? What is atomic number? Why carbon has mass number 12 Why valency of nitrogen is 3 not 5. Which model of atom is corelated with solar system?

80. Home assignments : 1.Compare the properties of electrons, protons and neutrons. 2. What are the limitations of J.J. Thomson’s model of the atom? 3. What are the limitations of Rutherford’s model of the atom? 4. Describe Bohr’s model of the atom. 5. Compare all the proposed models of an atom given in this chapter. 6. Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements. 7. Define valency by taking examples of silicon and oxygen. 8.If number of electrons in an atom is 8 and number of protons is also 8, then ( i ) what is the atomic number of the atom? (ii) what is the charge on the atom?

81. suggessions You are requested to insert your effects from different sources to make the lesson plan more interesting if you think so because it is not ultimate. Students are encouraged to corelate the knowledge with surrounding and in day today life.

82. Thank you

83. SRG Group(Science) Pradeep Kumar ( Lect.in Chem ) 9816645503 Dr. Dirghayu Prasad ( Lect.in Chem ) 9418028866 Manoj Sharma ( Lect.in Chem ) 9418605442