Page 1 : GVHSS PAYYOLI VICTERS PHYSICS CLASS NOTES 69 january 17, CHAPTER 12: ATOMS-2, Bohr Atom Model, ………………………………………………………………………………………………………, FAILURE OF RUTHER FORD’S ATOM MODEL, , (1) According to Rutherford’s atom model , electron, revolves round the nucleus in stable orbits and have, a centripetal acceleration. According to, electromagnetic theory an accelerating charged, particle emit radiations in the form of, electromagnetic waves. The energy of an, accelerating electron continuously decrease and, electron will spiral inward and finally fall into, nucleus.Thus an atom cannot be stable., (2) The revolving electron must emit a continuous, spectrum. But actually we observe a line spectrum., POSTULATES OF BOHR ATOM MODEL, , Bohr’s postulates are,, (1), , (2), , Sreeshyju K P & Jijesh M T ,HSST Physics, GVHSS Payyoli

Page 2 : (3), , Expression for velocity , Radius , energy of a, revolving electron, By Bohr’s postulate the angular momentum of nth, orbit is, , Comparing above two equations, , Substituting the values, , Where C is velocity of light, , Sreeshyju K P & Jijesh M T ,HSST Physics, GVHSS Payyoli

Page 3 : For first orbit n=1, There for radius of first orbit r1 = 0.5 A0, This radius is called Bohr radius, Also Energy of nth orbit is given by, , Substituting for rn, , Energy of first orbit , n=1(ground state ), E1 = -13.6 ev, Energy level diagram, ,  The energies of higher level become closer and, closer as n increases,  The highest energy state corresponds to n = ∞, and has energy of 0 eV, Sreeshyju K P & Jijesh M T ,HSST Physics, GVHSS Payyoli

Page 4 :  The lowest energy state of atom(for n=1,, E= -13.6eV) is called ground state. The, minimum energy required to free an electron, from the ground state is 13.6 eV and is called, ionization energy, , Energy of 𝑛𝑡ℎ orbit is, , Sreeshyju K P & Jijesh M T ,HSST Physics, GVHSS Payyoli