Atomic models

In the last century several atomic models emerged, but only three of them interest us. These are the Thomson, Rutherford and Bohr models.

Thomson model

The English physicist Joseph John Thomson (1856-1940) proposed, in 1904, an atomic model that consisted of a spherical volume charged with a positive electrical charge, surrounded by a set of charged electrons with a negative electrical charge. This model became known as plum pudding, which are represented by electrons, which, supposedly, were static and inserted into the spherical mass.

Thomson already knew that the total electrical charge of the atom was zero, that is, the positive and negative charges neutralized each other.

Rutherford model

The physicist Ernest Rutherford (1871-1937), in 1908, bombarded a thin gold plate with alpha particles, which constitute the nucleus of the helium gas atom. To Rutherford’s surprise, only a small amount of the particles were deflected. Most of them passed through the blade without being deflected.

The conclusion of this scientist was that the atom had a tiny nucleus responsible for the deflection of alpha particles. The large part of the atom would then be empty (a region in which the electrons were located). Rutherford compared his atomic model with the Solar System, in which the Sun would be a small nucleus and the planets, orbiting around it, would be electrons. For Rutherford, electrons have a negative electrical charge and the nucleus of an atom has a positive electrical charge. Since atoms have the same number of protons and electrons, their total electrical charge would be zero.

Bohr model

In 1913, the physicist Niels Bohr (1885-1962) took the model proposed by Rutherford and complemented it by noting that electrons could only move around the nucleus when arranged in certain orbits or energy levels. This means that the atomic model does not bear much resemblance to the solar system. For Bohr, if an electron received or donated energy, it would change its energy level, that is, it would jump to a more external orbit.

The explanation for why the electron never collided with the nucleus was given by the physicist Louis de Broglie. According to Broglie, an electron can revolve around the nucleus always at certain energy levels, as long as the length of its trajectory is equal to an integer number of wavelengths.

From Bohr’s atomic model to current models, only the idea of ​​the orbit has changed. Electrons do not describe well-defined orbits around the nucleus, as is the case with the movement of planets around the Sun. In 1925, it was already known that the behavior of the electron was dubious: sometimes as a wave, sometimes as a particle

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