What is the Bohr Model?
The Bohr Model, proposed by Niels Bohr in 1913, describes atoms as having electrons that orbit a central, positively charged nucleus in specific, stable energy levels or shells. Unlike earlier models, it postulated that electrons can only occupy these discrete orbits, preventing them from continuously losing energy and spiraling into the nucleus.
Key Principles of the Bohr Model
The model is built on three main postulates: (1) Electrons orbit the nucleus in specific, stable paths without radiating energy. (2) Each orbit corresponds to a quantized energy level; electrons can only jump between these orbits by absorbing or emitting a photon with an energy exactly equal to the difference between the two energy levels. (3) The angular momentum of an electron in an allowed orbit is also quantized, meaning it can only take on certain discrete values.
A Practical Example: The Hydrogen Atom
The Bohr Model successfully explained the observed spectral lines of the hydrogen atom. When an electron in a hydrogen atom absorbs energy, it jumps to a higher energy orbit. When it falls back to a lower energy orbit, it emits a photon with a specific wavelength and energy, which corresponds to the discrete lines seen in hydrogen's emission spectrum, such as the Balmer series in the visible light range.
Importance and Limitations
The Bohr Model was a significant leap forward, introducing the concept of quantized energy levels and providing an explanation for atomic stability and spectral lines. However, it has limitations; it only accurately predicts the spectra of single-electron atoms like hydrogen, struggles with multi-electron atoms, and does not account for the fine structure of spectral lines or the wave-particle duality of electrons, paving the way for more sophisticated quantum mechanical models.