Question

In what ways does the Franck-Hertz experiment DISAGREE with the Bohr model?

Answer 1

While Franck and Hertz were unaware of it when they published their experiments in 1914, in 1913 Niels Bohr had published a model for atoms that was very successful in accounting for the optical properties of atomic hydrogen

FRANCK-HERTZ EXPERIMENT WITH NEON

In instructional laboratories, the Franck–Hertz experiment is often done using neon gas, which shows the onset of inelastic collisions with a visible orange glow in the vacuum tube, and which also is non-toxic, should the tube be broken. With mercury tubes, the model for elastic and inelastic collisions predicts that there should be narrow bands between the anode and the grid where the mercury emits light, but the light is ultraviolet and invisible. With neon, the Franck–Hertz voltage interval is 18.7 volts, and an orange glow appears near the grid when 18.7 volts is applied. This glow will move closer to the cathode with increasing accelerating potential and indicates the locations where electrons have acquired the 18.7 eV required to excite a neon atom. At 37.4 volts two distinct glows will be visible: one midway between the cathode and grid, and one right at the accelerating grid. Higher potentials, spaced at 18.7-volt intervals, will result in additional glowing regions in the tube.

An additional advantage of neon for instructional laboratories is that the tube can be used at room temperature. However, the wavelength of the visible emission is much longer than predicted by the Bohr relation and the 18.7 V interval. A partial explanation for the orange light involves two atomic levels lying 16.6 eV and 18.7 eV above the lowest level. Electrons excited to the 18.7 eV level fall to the 16.6 eV level, with concomitant orange light emission.

NEILS BOHR MODEL

In atomic physics, the Rutherford–Bohr model or Bohr model, presented by Niels Bohr and Ernest Rutherford in 1913, is a system consisting of a small, dense nucleus surrounded by orbiting electrons—similar to the structure of the Solar System, but with attraction provided by electrostatic forces in place of gravity. After the cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911) came the Rutherford–Bohr model or just Bohr model for short (1913). The improvement to the Rutherford model is mostly a quantum physical interpretation of it. The model's key success lay in explaining the Rydberg formula for the spectral emission lines of atomic hydrogen. While the Rydberg formula had been known experimentally, it did not gain a theoretical underpinning until the Bohr model was introduced. Not only did the Bohr model explain the reasons for the structure of the Rydberg formula, but it also provided a justification for the fundamental physical constants that make up the formula's empirical results.

The Bohr model is a relatively primitive model of the hydrogen atom, compared to the valence shell atom model. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate quantum mechanics and thus may be considered to be an obsolete scientific theory. However, because of its simplicity, and its correct results for selected systems (see below for application), the Bohr model is still commonly taught to introduce students to quantum mechanics or energy level diagrams before moving on to the more accurate, but more complex, valence shell atom. A related model was originally proposed by Arthur Erich Haas in 1910 but was rejected. The quantum theory of the period between Planck's discovery of the quantum (1900) and the advent of a mature quantum mechanics (1925) is often referred to as the old quantum theory.

THAT WAS THE REGION