Atomic Theory I: Cathode Rays, Electrons and the Nucleus

Between 1908 and 1911, Ernst Marsden and Hans Geiger conducted a series of experiments under the direction of Ernest Rutherford of the University of Manchester, England. In these experiments, alpha particles (microplus charged particles) were fired on a thin gold foil (Fig. 3). In the Atomic Thomson Plum Pudding model, "uniformly positively charged spheres" are very dispersed, so small and fast-moving alpha particles pass directly. Similarly, since the electrons in the model are considered to be very small, the electrostatic interaction between them and the positive alpha particles is minimized and the path of alpha particles is hardly affected.

As expected, Rutherford and his colleagues observed that most of the alpha particles passed directly through the gilt and some of the particles were deflecting at a small angle. However, contrary to what the Plum Pudding model predicts, it may bounce at a very sharp angle or even return directly to the source. These particles seem to have encountered hard objects like tennis balls bounced off the brick wall (Figure 4).

The fact that most alpha particles pass directly through the gilt suggests to Rutherford that atoms are composed of most empty spaces. However, contrary to the Thomson plum pudding model, Rutherford's research shows that there are positively charged regions that are dense within the atom, resulting in observed repulsion and backscattering of alpha particles. Rutherford was shocked by these observations and had a famous proverb:

This is the wonderful event that happened in my life. Just as throwing a 15 inch cannon on a piece of paper, it is as incredible as it comes back to you. With this in mind, I noticed that this backscattering had to be the result of a single collision When I did calculations, as long as you do not use the highest quality system, I found that it is impossible to obtain orders of magnitude of magnitude as well. Atomic concentrations are concentrated in micronuclei. At that time, I thought of small centers and charged atoms.

In a series of experiments and papers (Rutherford, 1911, 1913, 1914), Rutherford has an atomic model with a dense, positively charged region and a nucleus I developed a model. An atom was born

Although no one actually saw the interior of the atom, many experiments have proven many atomic structures. Thomson's cathode ray tube shows that atoms contain small negatively charged particles called electrons. Milican found a basic charge-electron charge. The Rutherford gold leaf experiment shows that atoms have small, high density, positively charged nuclei; positively charged particles in the nucleus are called protons. Chadwick discovered that the nucleus also contains neutral particles called neutrons. Soddy proved that the atomic weights of the same elements are different; they are called isotopes

The atom itself is composed of three small particles called subatomic particles. Proton, neutron, and electron. Protons and neutrons form the center of the atom called the nucleus, and electrons jump over the nucleus above the small cloud. Electrons are negatively charged, and protons are positively charged. At normal (neutral) atoms, the number of protons is equal to the number of electrons. Usually, it is not always, but the number of neutrons is the same.

An atom is composed of three elementary particles: proton, electron, and neutron. Atomic nucleus (center) contains protons (positively charged) and neutrons (no charge). The outermost region of an atom is called an electron shell and contains electrons (negatively charged). Atoms have different characteristics based on the arrangement and number of their elementary particles. Proton and neutron mass are about the same, about 67 x 10 - 24 grams. Scientists define this mass as atomic mass unit (amu) or dalton. The masses are similar, but the protons are positively charged, but neutrons do not have electric charges. Therefore, the number of neutrons in an atom greatly contributes to its mass, but it does not contribute to its charge.