Write postulates and limitations of Bohr Hydrogen atomic model
Answers
It violates the Heisenberg Uncertainty Principle. The Bohr atomic model theory considers electrons to have both a known radius and orbit i.e. known position and momentum at the same time, which is impossible according to Heisenberg.
The Bohr atomic model theory made correct predictions for smaller sized atoms like hydrogen, but poor spectral predictions are obtained when larger atoms are considered.
It failed to explain the Zeeman effect when the spectral line is split into several components in the presence of a magnetic field.
It failed to explain the Stark effect when the spectral line gets split up into fine lines in the presence of an electric field.
Explanation:
Niels Bohr quantitatively gave the general features of hydrogen atom structure and it's spectrum. His theory is used to evaluate several points in the atomic structure and spectras. The postulates of Bohr atomic model for hydrogen as follows Postulates : → The electron in the hydrogen atom can revolve around the nucleus in a circular path of fixed radius and energy. These paths are called orbits (or) stationary states. These circular orbits are concentric (having same center) around the nucleus. → The energy of an electron in the orbit does not change with time. → When an electron moves from lower stationary state to higher stationary state absorption of energy takes place. → When an electron moves from higher stationary state to lower stationary state emission of energy takes place. → When an electronic transition takes place between two stationary states that differ in energy by ∆E is given by ∆E = E2 – E1 = hυ ∴ The frequency of radiation absorbed (or) emitted υ = (E2 − E1)/h and E2 are energies of lower, higher energy states respectively. → The angular momentum of an electron is given by mvr = nh/2π An electron revolve only in the orbits for which it's angular momentum is integral multiple of h/2π. Limitations : → Bohr's theory does not applicable to explain the Multi Electronic Systems Spectra. → This theory does not explained the fine structure of hydrogen atom. → It does not explained Zeeman effect and stark effect