Points to remember.
electrons have been discovered from cathode ray tube experiment in which scientist were interested in e/m ratio of the particles present inside the vaccum chamber of cathode ray tube.
charge of electrons and e/m ratio was discovered by Millikan through his Millikan’s oil drop experiment.
dicovery of proton in an experiment similar to CRT (cathode ray tube). in canal ray tube the e/m ratio depends on the gas taken inside the tube because the tube is filled with ionised gaseous atoms or ions.
from this it has been concluded that protons cannot be removed out of an atom only electron can be removed.
J.J Thompson’s Atomic model_
according to J.J thompson’s atomic odel , he stated that an atom is similar to watermelon where seeds of watermelon represents the negative charge and red flesh represents the positive charge. this atomic model failed because it could not properly explain the neutrality and stability of atom.
Rutherford’s atomic model
Rutherford gave his atomic model by taking the basis pf alpha-scattering experiment. in alpha scattering experiment , alpha particles are made to strike a gold foil and it was then observed that almost all aplha particles moving in a straight line. this obervation concludes that most of the atom is empty. only few particles were scattered in various direction and maximum 1 or 2 particles reflected back. this shows that all the positive charge is concentrated at a point . Rutherford atomic model failed because he could not explain the stabilty of atom.
bohr’s atomic model
according to Bohr’s atomic model_
1) positively charged nucleus is present in the centre of the atom and occupies negligible volume compared to the atom
2) the nucleus contains protons and neutrons.
3) electrons revolve around the nucleus in circular paths called as orbits.
4) all the electrons in an orbit have same energy.
5) this energy of an atom is referred as energy of orbit.
6) all the orbits of an atom posses different energy.
7) orbits which are near to nucleus have less energy as compared to those far from nucleus.
8)when electrons jumps from higher orbit to lower orbit , it releases energy in the form of electro- magnetic radiation.
9) if electrons jumps from lower orbit to hgher orbit then it absorbs energy in the form of electro magnetic radation
10) according to Bohr’s theory all the electrons in an orbit posses angular momentum