In this expression, \(k\) is a constant comprising fundamental constants such as the electron mass and charge and Planck’s constant. Explain why people believed in each model and why each historical model was inadequate. Explain what experimental predictions each model makes. Sample Learning Goals Visualize different models of the hydrogen atom. Check how the prediction of the model matches the experimental results. Bohr’s expression for the quantized energies is: Try out different models by shooting light at the atom. Instead of allowing for continuous values for the angular momentum, energy, and orbit radius, Bohr assumed that only discrete values for these could occur (actually, quantizing any one of these would imply that the other two are also quantized). The absolute value of the energy difference is used, since frequencies and wavelengths are always positive. In this equation, h is Planck’s constant and E i and E f are the initial and final orbital energies, respectively. ![]() Bohr's model and postulates do not explain this phenomenon.\] Spectral lines undergo splitting when a sample of gas is affected by an electric field (Stark effect) and magnetic field (Zeeman effect).These are referred to as hyperfine spectral lines. Bohr's model does not explain the presence of hyperfine lines. Each spectral line, when examined at higher magnification, actually consists of a number of smaller fine lines.The accuracy decreases as the effective nuclear charge of an atom or ion increases (due to greater number of protons). Predictions made by Bohr’s model is only accurate for the hydrogen atom.Bohr's model cannot predict the relative intensity (brightness) of the spectral lines.It is obtained by application of classical energy and momentum concepts together with a nonclassical quantization rule. In other words, his model does not explain why electrons can remain in their orbits without spiralling into the nucleus due to electrostatic attraction. The Bohr model for the hydrogen atom was among the earliest successes of quantum mechanics. Bohr does not provide an explanation to 'stationary states' of electrons.Circular motion of electrons is from classical physics while the quantisation of its momentum and energy of orbits is from quantum physics. Bohr's model combines principles from both classical and quantum physics.$$\Delta E_ J$$ Limitations of Bohr's Atomic Modelīohr's model of the atom has several limitations. The great Danish physicist Niels Bohr (18851962) made immediate use of Rutherford’s planetary model of the atom. An electron can transition between orbits by absorbing or releasing energy that is exactly equal to the difference in energy of orbits, consistent with the law of conservation of energy.Įlectron excitation occurs when an electron absorbs energy to move to an orbit of higher energy.Įlectron relaxation occurs when an electron moves to a lower orbit, releasing energy in the form of electromagnetic radiation (photon). In these orbits, electrons exist in 'stationary states' and do not emit energy.īohr’s model of the atom describes electrons orbiting in stable energy levels as opposed to Rutherford's model in which electrons' motion was not described.Ģ. ![]() Electrons revolve around the nucleus in circular orbits with discrete radii and quantised energies. Niels Bohr proposed three postulates in his atomic model:ġ. – Rydberg's equation Bohr's Model of the Atom
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