With the idea of the atom consolidated, several scientists were working in an attempt to propose a model that would significantly explain the observations and known experimental results. One such scientist was Rutherford who, in his model, explained the atom as having almost all of its mass in its positively charged nucleus and that negatively charged electrons revolve around this nucleus. However, by the laws of classical physics, this model could not exist, because, according to classical electromagnetism, electrons, like any charge in accelerated motion, when rotating around the nucleus, emit radiation and, when emitting this radiation, they emit radiation. lose energy. Thus, the electrons would lose all their energy and collide with the nucleus.
As it was necessary to create a model to explain atomic structure, in 1913 Bohr proposed an atomic model. His model was based on two postulates:
1st. Electrons can only rotate around the nucleus in circular orbits, these orbits are called stationary orbits and as long as they are in these orbits, they do not emit energy.
2nd. The energy absorbed or emitted by an atom is equivalent to a whole number of quanta.
Each quant has energy equal to hf , where f is the frequency of the radiation and h is Planck’s constant. Therefore, the change in energy produced in an atom will be equal to the energy emitted or received. This change in energy is given by:
E e – E i =h .f
E e : energy of the outermost (higher energy) orbit;
E i : energy of the innermost (lower energy) orbit;
h: Planck’s constant;
f: frequency of the absorbed or emitted photon.
Thus, an electron in a permissible orbit emits a photon of energy to go to another, less energetic permissible orbit, see figure 2.
During the jump, to go from a higher energy orbit to a lower energy one, the electron emits a photon with energy equal to:
E 1 – E 2 =h .f
Now, look at figure 2, for an electron to go from a permissible orbit to another one that is also more external, that is, more energetic, it needs to absorb a photon of energy that contains the exact energy for it to change orbits.
During the jump, to go from a lower energy orbit to a higher energy one, the electron absorbs a photon with energy equal to:
E 2 – E 1 =h .f
It is important to emphasize that Niels Bohr’s hypotheses aimed to explain the behavior of the electron movement around the nucleus of the hydrogen atom and that it was not deduced from already known theories. Despite being able to explain the movement of the electron in the hydrogen atom, the model proposed by Bohr did not obtain the same result when applied to atoms of other elements, not solving the problem of atomic structure. This is where quantum mechanics comes in, to more satisfactorily explain atomic structure.