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Structure of atom

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Structure of atom

  5. 5. TITLE Slide • INTRODUCTION 8-10 • CONTENT 11-50 -What Is An Atom? 12-14 -Thomsons Model 15-19 -Discovery Of Protons 20-21 -Discovery Of Neutrons 22-23 -Rutherfords Model 24-33 -Bohrs Model 34-40 -Subparticles In Atom 41-46 -Valency 47 - Atomic Number 48 -Mass Number 49 -Isotopes 50-51 -Isobars 52 • CONCLUTION 53-54 • TEAM MEMBERS 55 • REFERENCE 56
  6. 6. INTRODUCTION Atom was discovered by John Dalton. He proposed the famous atomic theory in 1807. Atoms are fundamental unit of matter. The existence of different kinds of matter is due to different atoms constituting them.
  7. 7. A major challenge before the scientists at the end of the 19th century was to reveal the structure of the atom as well as to explain its important properties. Many scientists worked hard and proposed many models for the atom, here we are going to learn about the structure of an atom
  8. 8. STRUCTURE OF AN ATOM The discovery of the two fundamental particles (electrons and protons) inside the atoms led to the failure of the aspect of Daltons atomic theory. For explaining the arrangement of electrons and protons in an atom, many scientists proposed various atomic models.
  9. 9. CONTENT
  10. 10. All matter is made up of atoms. Atoms of an element are identical. Each element has different atoms. Atoms can engage in a chemical reactions. Atoms can neither be created nor be destroyed. Atoms are indivisible. Atomic Theory John Dalton (1776-1884)
  11. 11. Thomson’s Plum Pudding Model In 1897, the English scientist J.J.Thomson provided the first hint that an atom is made of even smaller particles.
  12. 12. Thomson Model • He proposed a model of the atom that is sometimes called the “Plum Pudding” model. • Atoms were made from a positively charged sphere with negatively charged electrons embedded in it, like raisins in a pudding. • The negative and positive charges are equal in magnitude.So,the atom as a whole is electrically stable
  13. 13.  Passing an electric current makes a beam appear to move from the negative to the positive end. Thomson’s Experiment And Discovery of Electrons Voltage source +-
  14. 14. Voltage source Thomson’s Experiment  By adding an electric field he found that the moving pieces were negative. He called these moving pieces “electron” + -
  15. 15. The electron was discovered in 1897 by Thomson. He imagined the atom as a “raisin pudding” with electrons stuck in a cake of positive charge.
  16. 16. Discovery of Protons • Eugene Goldstein noted streams of positively charged particles in cathode rays in 1886. –Particles move in opposite direction of cathode rays. –Called “Canal Rays” because they passed through holes (channels or canals) drilled through the negative electrode.
  17. 17. Canal rays must be positive. Goldstein postulated the existence of a positive fundamental particle called the “proton”.
  18. 18. DISCOVERY OF NEUTRONS In 1932, J. Chadwick discovered another subatomic particle which had no charge and a mass nearly equal to that of a proton. It was eventually named as neutron. Neutrons are present in the nucleus of all atoms, except hydrogen. In general, a neutron is represented as ‘n’. The mass of an atom is therefore given by the sum of the masses of protons and neutrons present in the nucleus.
  19. 19. NEUTRONS
  20. 20. Rutherford’s Gold Foil Experiment • In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure.
  21. 21. • Rutherford’s experiment Involved firing a stream of tiny positively charged alpha (α) particles at a thin sheet of gold foil. • The expected result was that the α- particles would be deflected by the sub- atomic particles in gold atoms. Since α - particles were much heavier than protons, he did not expect to see larger deflections
  22. 22.  Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all.  Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.
  23. 23.  This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material.  Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.”  He called the center of the atom the “nucleus”  The nucleus is tiny compared to the atom as a whole.
  24. 24. Rutherford’s Postulates Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge.
  25. 25. Solar system Rutherford‘s atom model Planetary model of atom
  26. 26. The model created by Rutherford had still some serious discordance. According to the classic science, electron moving around the nucleus or the planetary model of atom,is unstable. Because ,in the planetary model of atom, the electron should radiate energy and finally fall in to the nucleus.
  27. 27. Bohr’s Model In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level.
  28. 28. Following Rutherford’s planetary model of the atom, it was realized that the attraction between the electrons and the protons should make the atom unstable Bohr proposed a model in which the electrons would stably occupy fixed orbits, as long as these orbits had special discrete locations
  29. 29. Bohr’s Model Nucleus Electron Orbit Energy Levels
  30. 30. Bohr's Model of the Atom  The special orbits known as discrete orbits of electron are allowed inside an atom. These orbits or shells are represented by the letters K,L,M,N,….. Or the numbers ,n=1,2,3,4,….
  31. 31. Bohr's Model of the Atom  electrons fills the orbits closest to the nucleus e.g. fluorine: #P = 9 #e- = 9 #N = 10 9P 10N F 19.00 9
  32. 32. Each orbit can hold a specific maximum number of electrons An easy way to calculate the total number of electrons that can be held by a given energy level is to use the formula 2*n2 Shell maximum no: of electrons 1 - K 2*12= 2 - L 2*22= 3 - M 2*32= 4 - N 2*42= Bohr's Model of the Atom 2 8 18 32
  33. 33. Key aspects of Bohr’s model • Electrons move around the nucleus at stable orbits without emitting radiation. • Electron in one of these stable orbit has a definite energy. • Energy is radiated only when electrons make transitions from high energy orbit to a low energy orbit.
  34. 34. What is in the structure of an atom? • Nucleus - center of the atom Home of Protons and Neutrons Has a positive charge • Proton Has a relative mass of 1u Has a positive (+) charge Determines the atomic number Found inside the nucleus
  35. 35. What is in the structure of an atom? • Neutron Has no (0) charge Has a relative mass of 1u Found inside the nucleus
  36. 36. What is in the structure of an atom? • Electron Has a negative (-) charge Found outside the nucleus • Rutherford atom model - electrons are around the nucleus • Bohr model – electrons are in specific energy levels called shells
  37. 37. How are p, n, e related? • No. protons = No. electrons • No. protons = atomic number • No. protons + No.neutrons = mass number • No. neutrons=mass no. - atomic no.
  38. 38. • The outermost shell of an atom is known as its valence shell. • The electrons present in the outermost shell of an atom are known as the valence electrons • The Valency of an element may be defined as the combining capacity of its atoms with atoms of other elements in order to acquire octet configuration. • For eg; The valency of hydrogen is 1.
  39. 39. • The number of protons in an atom is referred to as its Atomic Number. • It is denoted by the letter ‘ Z ’. • Elements are defined by the number of protons they posses. • The atomic number of hydrogen is 1.
  40. 40. • The mass of an atom resides in its nucleus. The mass of an atom is practically due to protons and neutrons alone. • Therefore, Mass Number of an atom is the sum of neutrons and protons present in the nucleus of an atom • for hydrogen, its mass number is 1u.
  41. 41. • Isotopes are atoms of same element, which have different mass numbers but same atomic number. • Their chemical properties are similar but physical properties are different.
  42. 42. • An isotope of uranium is used as a fuel in nuclear reactors. • An isotopes of cobalt is used in the treatment of cancer. • An isotope of iodine is used in the treatment of goitre.
  43. 43. • Atoms of different elements with different atomic numbers ,which have the same mass number are known as isobars. • Examples of isobars are: calcium(z=20)and argon(z=18).their mass number is 40 u.
  44. 44. CONCLUSION • Atoms are the building blocks of matter. • Thomsons atom model is that atom is a positively charged sphere and the electrons are embedded in it and atoms are neutral. • Rutherford did the famous gold foil experiment and said that there is a positively charged centre in an atom called nucleus and the electrons revolve around the nucleus in circular paths.
  45. 45. • Bohr was the next person. He proposed that only special discrete orbits are allowed inside an atom and while revolving electrons doesn’t radiate energy. • The sub particles in a nucleus is electron, proton and neutron. • Valency is the combining capacity of atoms. • Atomic number is the number of proton • Mass number is the sum of the number of neutron and protons in an atom. • Isotopes are atoms of the same element, which have different mass number and same atomic number. • Isobars are atoms which has same mass number but different atomic number,
  46. 46. TEAM MEMBERS
  47. 47. REFERENCE • Class IX Science Text • Wikipedia • Google
  48. 48. JOHN DALTON John Dalton was born in a poor weaver’s family in 1766 in England. He began his career as a teacher at the age of twelve. Seven years later he became a school principal. In 1793, Dalton left for Manchester to teach mathematics, physics and chemistry in a college. He spent most of his life there teaching and researching. In 1808, he presented his atomic theory which was a turning point in the study of matter. Back
  49. 49. J.J.Thomson J.J. Thomson (1856- 1940), a British physicist, was born in Cheetham Hill, a suburb of Manchester, on 18 December 1856. He was awarded the Nobel prize in Physics in 1906 for his work on the discovery of electrons. He directed the Cavendish Laboratory at Cambridge for 35 years and seven of his research assistants subsequently won Nobel prizes. Back
  50. 50. E .Rutherford Ernest Rutherford, (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist who became known as the father of “nuclear physics .He was born at Spring Grove on 30 August 1871. He was known as the ‘Father’ of nuclear physics. He is famous for his work on radioactivity and the discovery of the nucleus of an atom with the gold foil experiment. He got the Nobel prize in chemistry in 1908. Back
  51. 51. NEILS BOHR • Niels Henrik David Bohr (7 October 1885 – 18 November 1962) was a Copenhagen born Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. Bohr was also a philosopher and a promoter of scientific research. • He was appointed professor of physics at Copenhagen University in 1916. Among Professor Bohr’s numerous writings, three appearingas books are: (i) The Theory of Spectra and Atomic Constitution, (ii) Atomic Theory and, (iii) The Description of Nature. Back