Sunday, July 13, 2008

Bohr’s model - laws and models

Thomson model

Lenard’s suggestion

Rutherford’s model

Balmer’s equation for wavelengths of hydrogen atomic spectra

Rydberg equation for wavelengths of hydrogen atomic spectra

Bohr model

The proposals of Bohr are termed as postulates

1. The electron revolves round the nucleus in circular orbits.

2. the circular orbits take only some special values of radius. In these orbits, the electron does not radiate energy, even though it is rotating around the nuclues. Radiation is expected from Maxwell's laws. But Bohr's conception is that electrons in the special radius orbits do not radiate energy.

3. The energy of the atom has a definite value when electrons of the atom are in specified stationary orbits. The electrons can jump from one stationary orbit another. If an electron jumps from an orbit of higher energy E2 to an orbit of lower energy E1, it emits a photon with energy equal to E2-E1.

The wavelength of the radiation of the photon (in wave nature theory) will be determined according to E2-E1 = hc/λ.

The electron can absorb energy from some source and jump from a lower energy orbit to a higher energy orbit also.

4. In the stationary orbits (orbits are stationary not the electrons) the angular momentum l of the electron around the nucleus is an integral multiple of the Planck constant h divided by 2π,

l = nh/2π

The last postulate is called Bohr's quantization rule.

Schrodinger’s wave equation

Pauli exclusion principle

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