Question

why electron does not fall into nucleus (drawback of Rutherford at modl).? How energy is not radiated by the electron in the orbit in which its revolving the nucleus.

Answer 1

Electrons bound in atoms are described by "standing wavefunctions" (electron orbitals) that are waves that remains in a constant position. These electron orbitals occupy nonradiating states, as opposed to the classical model according to which an electron should radiate energy and spiral into the nucleus.

In 1909 Ernest Rutherford discovered that the positive half of atoms was tightly condensed into a nucleus, and it became clear from his analysis in 1911 that the plum pudding model could not explain atomic structure.

Shortly after, in 1913, Rutherford's postdoctoral student Niels Bohr proposed a new model of the atom, wherein electrons orbited the nucleus with classical periods, but were only permitted to have discrete values of angular momentum, quantized in units h/2π. This constraint automatically permitted only certain values of electron energies.

The Bohr model of the atom fixed the problem of energy loss from radiation from a ground state (by declaring that there was no state below this), and more importantly explained the origin of spectral lines.