What is the excited state of an atom

In 1905, J. Thomson proposed the first model of the structure of the atom, according to which it is a positively charged sphere inside which particles with a negative charge are located - electrons. The electric neutrality of the atom was explained by the equality of the charges of the sphere and all its electrons.

To replace this theory in 1911 came the planetary model created by Rutherford: in the center the core-star, which constitutes the bulk of the entire atom, orbits around it rotate planet electrons. However, in the future, the results of the experiments questioned the correctness of this model. For example, it follows from Rutherford's formulas that the electron velocities and their radii can change continuously. In this case, continuous radiation would be observed throughout the spectrum. However, the results of the experiments indicate linear spectra of atoms. There are also some other contradictions. Subsequently N. Bohr proposed a quantum model of the structure of the atom. It is necessary to note the ground and excited state of the atom. This characteristic allows, in particular, to explain the valence of the element.

The excited state of an atom is an intermediate stage between a state with zero energy level and exceeding it. It is extremely unstable, therefore it is very fleeting - the duration is a millionths of a second. The excited state of an atom occurs when additional energy is communicated to it. For example, its source can be the acting temperature and electromagnetic fields.

In a simplified form, the classical theory of atomic structure asserts that negatively charged indivisible particles, electrons, rotate around the nucleus at certain distances along circular orbits. Each orbit is not a line, as it may seem, but an energy "cloud" with several electrons. Additionally, each electron has its own spin (rotates around its axis). The radius of the orbit of any electron depends on its energy level, therefore, in the absence of external influence, the internal structure is sufficiently stable. Its violation - the excited state of the atom - occurs when the external energy is communicated. As a consequence, in the last orbits, where the force of interaction with the nucleus is small, the pairwise spins of the electrons decay and, as a consequence, their transition to unoccupied cells. In other words, in accordance with the law of conservation of energy, the transition of an electron to higher energy levels is accompanied by the absorption of quanta.

Let us consider the excited state of an atom on the example of an arsenic atom (As). Its valence is three. Interestingly, this value is only valid for the case when the element is in a free state. Since the valence is determined by the number of unpaired spins, when the atom receives an external energy in the region of the last orbit, a pairing is observed with the transition of the particle to a free cell. As a result, the orbit changes. Since the energy sublevels simply change places, the transition back (recombination), to the ground state of the atom, is accompanied by the release of the equivalent of the absorbed energy in the form of quanta. Returning to the example with arsenic: due to the change in the number of unpaired spins in the excited state, the valence of the element corresponds to five.

Schematically, all of the above is as follows: when external energy is supplied from outside by an atom, external electrons are displaced a greater distance from the nucleus (the radius of the orbits increases). However, since the proton remains in the nucleus, the total value of the internal energy of the atom becomes larger. In the absence of a continuous supply of external energy, the electron very quickly returns to its former orbit. In this case, the excess of its energy is released in the form of electromagnetic radiation.