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 x 10 -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.
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.
The radius of the orbit is such that the angular momentum of the electron is an integral multiple of h/2p.
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.
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 energy is 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 ³ h / 4π