Atomic Model (Part 4: The Rutherford's Atomic Model)

A few years later after Thomson put forward his theory, then his student named Ernest Rutherford along with Geiger and Marsden carried out an experiment by shooting the alpha (α) on a thin gold plate to prove the Thomson's atomic theory. Based on the result of the experiment, Rutherford proposed an atomic theory or model as follow.

• An Atom consists of an atomic nucleus which is positively charged. The nucleus of atom contains almost entire mass of the atom and is surrounded by electrons which are negatively charged as in the solar system model.
• Entirely, an atom is neutral because the number of its positive charges (proton) is equal to that of its negative charges.
• During revolving the nucleus, the centripental forces on electron in an atom is produced by the force of attraction between the electrons and nucleus (Coulomb force).

Basically, Rutherford's atomic theory is better than Thomson's atomic theory. However, this theory has some weaknesses. The first one is: it disagrees with the Maxwell's theory (electromagnetic wave theory). Based on the electromagnetic wave theory, the electrically charged particles which move with an accelaration such as the electron wave radiation.

Because electrons are negatively charged particles, in accordance with the electromagnetic wave theory, during revolving the nucleus electrons will emit energy continuously, then they will lose the energy and finally fall  onto the nucleus. In this case, if Rutherford's atomic theory is true, the path of electron in revolving the nucleus will be spiral, but in fact it never occurs.

In additional to its disagreement with the electromagnetic wave theory, Rutherford's atomic theory has the second weakness, namely the inability to explain the phenomena of line spectrum of hydrogen atom. If the Ruthrford's atomic theory is true, during revolving the nucleus, electrons will emit eletromagnetic waves (light) continously,  but in fact the spectrum of hydrogen atom is not a continous spectrum, rather than a aline spectrum (discreet spectrum).