explain bhor's postulate of hydrogen atom
Answers
Postulates of Bohr’s Hydrogen atom:
1. An atom has a number of stable orbits in which an electron can reside without the emission of radiant energy. Each orbit corresponds, to a certain energy level.
2. An electron may jump spontaneously from one orbit (energy level E1) to the other orbit (energy level E2, where E2 > E1); then the change in energy in the electron jump is given by Planck’s equation:
∆E = E2-E1= hv
Where h = Planck’s constant , v = frequency of light emitted.
3. The motion of an electron in a circular orbit is restricted in such a manner that its angular momentum is an integral multiple of h/2π, Thus
mvr = nh/2π, where m = mass of the electron
v = velocity of the electron , r = radius of the orbit an
n = an integer called principal quantum number of the electron.
4. A special surface around nucleus which contained orbits of equal energy and radius was called shell. The 'energy levels' or 'shells' or 'orbits' are represented in two ways: either by the numbers 1, 2, 3, 4, 5 and 6 or by letters K, L, M, N, O and P. The energy levels are counted from centre outwards.
5. Each energy level is associated with a fixed amount of energy. The shell nearest to the nucleus has minimum energy and the shell farthest from the nucleus has maximum energy. • There is no change in the energy of electrons as long as they keep revolving with the same energy level. But, when an electron jumps from a lower energy level to a higher one, some energy is absorbed while some energy is emitted.
The importance of this model to exxplain the various series of line spectra in hydrogen atom:
Bohr tells us that the electrons in the Hydrogen atom can only occupy discrete orbits around the nucleus where they do not radiate energy.
When the electron moves from one allowed orbit to another it emits or absorbs photons of energy matching exactly the separation between the energies of the given orbits (emission/absorption spectrum).
We see these photons as lines of coloured light (let’s say, the Balmer Series) in emission or dark lines in absorption.