Electron was discovered during experiments on the discharge
of electricity through rarified gases. The magnitude of electric
charge (e) was determined by Millikan. Charge of the electron =
1.602 X10 -19 coulomb
Bohr Model of the Atom:
Proposed by Neil Bohr in 1913. Bohr applied the Planck�s
quantum theory to the Rutherford nuclear atom with remarkable
success.
First postulate:
An atom consists of a positively charged nucleus at the
centre. The electrons move round the nucleus in certain
stationary orbits of definite radii and not all possible radii.
Second postulate:
The radius of the orbit is such that the angular momentum of
the electron is an integral multiple of h/2p.
Third postulate:
Electron may jump from one orbit to the other, in which case
the difference in energy between the two states of motion is
radiated in the form of a light quantum.
X-Rays :
Invisible electromagnetic radiations, Wavelengths range
form 0.010A � 100A. These are discovered by Roentgen. When a
fast moving electron is suddenly stopped a part of its kinetic
energyis converted into X-ray photon the rest of the energy is
converted into heat.
Wave Particle Duality:
To understand any given experiment, we must use either the
wave or the photon theory, but not both. Light sometimes behaves
like a wave and some times like a particle
de Broglie Hypothesis:
Photons are treated as �packets of light� behaving like a
particle. Momentum of a photon: p = E / c = h/l Energy of a
photon: E = hc/l
Heisenberg Uncertainty Principle:
If position is identified the momentum cannot be measured.
If momentum is measured the position is lost. Dx X Dp � h /
4π
