After John Thomson discovered the electron the idea of the indivisible atom crashed. All because electrons emerged to be constituents of atoms. A new model of the world of the micro scale was needed.

The scientist who created such a model was nobody else but the discoverer of the electron - Joseph John Thomson. He came to the conclusion that each and every atom consisted of a homogenous sphere of positive electricity. Inside the sphere negative electrons were to rotate on some orbits round the sphere centre. The whole range of negative charge collected on electrons should be the same as the range of positive charge collected on the sphere surface. Transferring energy to electrons we increase their velocity and thereby develop orbits, on which the electrons go. Given enough energy they can leave their atom. Thomson model of the atom was called "the plum pudding" one because electrons in a sphere of the positive charge were situated like plums in a pudding (Let's brush aside the fact that plums don't move, or do they?)

The plum pudding model wasn't a long lasted one. In 1909 Ernest Rutherford and his students conducted an experiment showing that the idea was wrong. The experiment consisted in directing a beam of alpha particles (they have the positive charge) on a thin gold foil. When passing through the foil particles were scattered in different directions because of the influence of gold atoms. The scientists determined directions of the scattering. Of course Thomson theory predicted the scattering but it emerged that the prediction was not in agreement with data from the experiment. The most unexpected was the fact that some number of particles were deflected by the gold foil and moved in the opposite direction than in the beginning. The "plum pudding" model didn't anticipate such phenomenon. In that model positive charge was just distributed too regular to influence an alpha particle so strongly to repulse it. Something was wrong with that plum pudding!

Rutherford collected all the experimental data and began analysing them. In 1911 the new model of the atom was ready. According to Rutherford atom consisted of a tiny nucleus with all the positive charge gathered in it. Around the nucleus there were electrons circulating on some orbits. That idea explained the experiment. Some alpha particles got very close to the nucleus. Both alpha particles and nuclei have a positive charge. The force was strong enough to repel the particles. Also from this experiment we know the maximal size of a nucleus. Its size is 10^-14, to 10^-15 meters. Electrons are rotating around a nucleus on the area of about 10^-10 meters. So the nucleus is over 10000 times smaller than the whole atom. Almost the whole mass of the atom is however gathered in the nucleus. That is over 99,9%!

The Rutheford model of the atom was called the "planetary" one because according to it electrons move around a nucleus just like planets move around the sun. It explained the experimental data very well but still had some serious discordance. According to the classical science, an electron moving around the nucleus should emit an electromagnetic wave. That kind of emission is connected with the escape of some energy from the electron-nucleus configuration. As the energy of an electron decreases, the distance between the electron and the nucleus decreases too. So electrons shouldn't move round but spirally and finally collide with the nucleus. Anyway such phenomenon wasn't observed. Atoms of the most elements are stable. Other discordance regarded the radiation emitted by an atom- this problem we will discuss on the next page. Why doesn't a nucleus disintegrate although it has a very gig charge was also a serious question.

As we see the model of the atom created by Rutherford couldn't be the conclusive model of matter's constitution.