Explanation
In α-particle scattering experiment, Rutherford found a small number of a-particle. Which were scattered back through an angle approaching to 180°. This is possible only if the positive charges are concentrated at the centre or nucleus of the atom
We know that an electron is very light particle as compared to an a-particle. Hence electron cannot scatter the a-particle at large angles, according to law of conservation of momentum. On the other hand, mass of nucleus is comparable with the mass of a-particle, hence only the nucleus of atom is responsible for scattering of a-particles
Factual
The penetrating power is maximum in case of gamma rays because gamma rays are electromagnetic radiations of very small wavelength
β-particles, being emitted with very high speed compared to α-particle, pass for very little time near the atoms the medium. So the probability of the atoms being ionised is comparatively less. But due to this reason, their loss of energy is very slow and they can penetrate the medium through a sufficient depth
Neutron is about 0.1 more massive than proton. But the unique thing about the neutron is that while it is heavy, it has no charge (it is neutral). This lack of charge gives it the ability to penetrate matter without interacting as compared to the beta particles or alpha particles
Bohr postulated that electrons in stationary orbits around the nucleus do not radiate
This is the one of Bohr’s postulate. According to this the moving electrons radiates only when they go from one orbit to the next lower orbit
Rutherford confirmed that the repulsive force on α-particle due to nucleus varies with distance according to inverse square law and that the positive charges are concentrated at the centre and not distributed throughout the atom
According to classical electromagnetic theory, an accelerated charged particle continuously emits radiation. As electrons revolving in circular paths are constantly experiencing centripetal acceleration, hence they will be losing their energy continuously and the orbital radius will go on decreasing, form spiral and finally the electron will fall in the nucleus
According to postulates of Bohr’s atom model , the electron revolves around the nucleus in fixed orbit of definite radii. As long as the electron is in a certain orbit it does not radiate any energy
When the atom gets appropriate energy from outside, then this electron rises to some higher energy level. Now it can return either directly to the lower energy level or come to the lowest energy level after passing through other lower energy levels, hence all possible transitions take place in the source and many lines are seen in the spectrum
Nuclear force is nearly same for all nucleus
Electron capture occurs more often than positron emission in heavy elements. This is because if positron emission is energetically allowed, electron capture is necessarily allowed, but the reverse is not true, i.e., when electron capture is energetically allowed, positron emission is not necessarily allowed
According to Bohr’s second postulate
Lyman series Lies in the UV region
Energy required to ionise helium atom = 24.6 eV
Ionization energy = Binding energy
Bohr postulated that the angular momentum of the electron is conserved
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