ATOMS

ATOMS

The conclusion drawn from the alpha particle scattering experiments are

The positive charge of the atom is concentrated in a small core called the nucleus.

The whole mass of the atom remains in a small region of atom and the space around the nucleus is almost empty.

The shortest distance between the alpha particle and nucleus, when the kinetic energy of alpha particles becomes equal to the potential energy of alpha particle-nucleus system, is called the distance of closest approach of alpha particle during a head on collision.

Drawback of Rutherford atom model are, he could not explain the stability of atoms and origin of line spectrum.

According to Bohr, the angular momentum of the electrons is an integral multiple of h/2π. An electron does not radiate energy when it is in stationary orbit. Electrons radiate energy when the electron jumped from permitted high energy orbit to the lower energy orbit.

The difference between the energies between two states is radiated as a photon of energy hv.

The innermost orbit with n=1 is called the ground state. Other energy levels with n=1,2,3,… are called exited states.

The spectrum of light emitted by sun is called this solar spectrum and is found to be crossed by a large no. of dark and fine lines.

The energy required to raise an atom from its normal state to the exited state is called the excitation potential of the atom.

The ionization potential of an atom is the energy required to remove an electron from the ground state to an infinite distance from the nucleus.

The various quantum numbers needed to specify the state of an atom are 1.  The principal quantum number  2.the orbital quantum no. 3. Magnetic orbital quantum number  4.spin quantum no.

Pauli’s exclusion principle states that “no two electrons in an isolated atom can have the same values for all quantum numbers”.

X- Rays are electromagnetic waves having wavelength from 0.5 A 15A. X-Rays of long wavelength are called soft x-rays and that of short wavelength are called hard x-rays.

x-rays are produced when fast moving electrons are suddenly stopped by a target.

The intensity of x rays depend on the number of electrons further depend on the filament current.

The quality of x rays depend upon its penetrating power depend on the p.d. across the tube.

X rays are electromagnetic waves. They are not deflected in electric or magnetic field. The affect photographic plate. They can penetrate matter.

Moseley’s law states that the frequency of the spectral line in a x ray spectrum varies as the square of atomic number of the elements emitting it.