Rutherford Model Nucleus and Electrons
Ernest Rutherford and his students describe the gold foil experiment to provide an atomic model in two parts, the nucleus of an atom and extranuclear electrons. The presence of free charge electron was observed in the gas discharge tube established the fact that metals on specific heat give off electrons. These prove negatively charge particles present in the atoms but the whole atom is electrically neutral. Therefore, Rutherford, Geiger, and Marsden study the scattering experiment in physics and chemistry and beam of alpha particle obtained from spontaneously radioactive decay of polonium isotopes directed to very thin platinum or gold foil. The direction of motion of α-particles after emerging from the crystalline thin metal sheets traced on a fluorescent screen.
Rutherford Gold Foil Experiment Observations
- Rutherford observed that the vast majority of the alpha particles passed the straight line through the gold foil. This suggested that the chemical elements or matter consist largely of emptiness.
- But a very limited few particles (about 1 in 8000) changed their direction quite sharply but in some cases the deflection more than 90°.
- Even in a few cases, the alpha particle after the encounter moved backward or reflected back. But this number increases with the change metal foil of the heavier periodic table elements.
Conclusions of Gold Foil Experiment
Earnest Rutherford concluded these point from his gold foil experiment
- All the positive charge and the entire mass number of the atom concentrated in a very small part of the atom. These central core called the atomic nucleus.
- The dimensions of the nucleus are negligible compared to the atom. The Radius of the atomic nucleus ∼ 10-13 being the same as that of an electron but the radius of an atom ∼ 10-8. Thus an atom must have a very empty structure.
- The large deflection of an alpha particle from its original path was due to Coulombic repulsion between the alpha particle and the positive charge particle of an atom. Hence entire positive charge also resides in the central part of an atom.
- Some alpha particle suffers little deflection while passing by an electron. This suggested, outside the nucleus, there are electrons that make the atom ultimately neutral.
From the above conclusions, Rutherford proposed an atomic model for learning chemistry or physics in atomic science.
Rutherford Atomic Nucleus
According to the Rutherford model, the entire mass of the atom concentrated in a tiny positively charged nucleus. These electrons move around the nucleus in different orbits constantly otherwise the electrons fall on the nucleus. Thus an atom divided by Rutherford into two-parts, the nucleus of an atom and extranuclear electrons. For an example of the hydrogen atom, one electron move around the nucleus but other elements contain shielding electron.
Nucleus and Extranucler Electrons
Almost the entire mass of the atom concentrated in a very small central core called the nucleus of an atom. Since the extranuclear electrons contribute negligibly to the total mass of the atom. Therefore, the nucleus must carry particles that account both for the mass and positive charge of the atom.
Outside the nucleus, there are Z electrons, called extranuclear electrons. These electrons move around the nucleus in different energy levels constantly. When the electron moving in circular orbits or energy levels around the nucleus, the Coulombic attraction was balanced by the centrifugal force of attraction. Otherwise, the electrons fall on the nucleus. Therefore, these arrangements quite similar to the solar system in our environment.
Limitations of Rutherford Atomic Model
- The Rutherford model has limitations for conformity with the classical atomic theory of electromagnetic spectrum radiation. A moving charged particle always emits radiation with specific wavelengths. Thus the loss of kinetic energy and eventually hit the nucleus of an atom.
- If the energy of electron loses continuously, the observed atomic spectra should be continuous, which consisting of broad bands merging one into the other.