Tuesday, 26 April 2016

Thomson atomic model




From  the  study  of  discharge  of  electricity through  gases,  it became  clear  that  an  atom consists of   positive   and   negative   charges J.J. Thomson  tried  to  explain  the arrangement  of positive  charge  and the    electrons    inside    the atom. According   to   him,   an   atom   is   a sphere  of  positive  charge  having  a radius  of the  order  of  10 angstrom.  The positive charge is uniformly distributed  over  the  entire  sphere  and  the  electrons  are  embedded  in the  sphere  of  positive  charge. The  total  positive charge inside the atom is equal to the total negative charge carried by the  electrons,  so  that  every  atom  is  electrically  neutral.According  to Thomson,  if  there  is  a  single  electron  in  the  atom( hydrogen  atom), the  electron  must  be  situated  at  the  center  of the positive sphere. For an atom with two electrons (helium atom), the electrons should be situated symmetrically with respect to the center of the  sphere  i.e opposite  sides  of  the  center  at  a  distance  of  2r,  where r  is the radius of the positive sphere. In a three electron system of the atom, the electrons should be at the corners of a symmetrically placed equilateral  triangle,  the  side  of  which  was  equal  to  the  radius  of  the sphere.   In   general,   the   electrons   of   an   atom are located in   a symmetrical  pattern  with  respect  to  the  center  of  the  sphere. It  was  suggested  that  spectral  radiations  are  due  to  the  simple harmonic  motion  of  these  electrons  on  both  sides  of  their  mean positions. Moreover, the stability of the atom was very well explained on the  basis  of  this  model.