In 1905, George. Thomson proposed the first model of the atom, according to which it is a positively charged ball, inside of which are arranged particles with a negative charge - the electron.Electrically neutral atoms was explained by the equality of charges of the ball and all of its electrons.
replaced this theory in 1911, came to the planetary model created by Rutherford: in the center of the core star, make up the bulk of all atoms in orbits around the electrons spin-planet.Later, however, the results of experiments questioned the accuracy of the model.For example, of the formulas Rutherford indicated that the speed of the electrons and their radii can be continuously varied.In such a case it would be observed throughout the continuous emission spectrum.However, the results of experiments indicate the line spectra of atoms.There are also some other differences.Later, Niels Bohr proposed the quantum model of the atom.It should be noted ground and excited states of the atom.This feature allows, in particular, to explain the valence of the element.
excited states of atoms is an intermediate stage between the state of the zero-energy and exceeding it.It is unstable, so it is very fleeting - the duration of millionths of a second.Excited states of atoms occurs when the communication of the additional energy.For example, it may be the source of the influence of temperature and electromagnetic fields.
In simplified form, the classical theory of atomic structure claims that around the nucleus at certain distances in circular orbits revolve negatively charged indivisible particles - electrons.Each orbit is not a line, as it may seem, and the energy "cloud" with a few electrons.In addition, each electron has its own spin (rotate around its axis).The radius of the orbit of any electron depends on its energy level, so in the absence of external influences the internal structure is stable enough.Its infringement - excited states of atoms -nastupaet when reporting foreign energy.As a result, in the last orbits, where the power of interaction with the nucleus is small, paired electron spins are steamed, and, as a result, is their transition to an unoccupied cell.In other words, according to the law of conservation of energy transition of an electron to a higher energy levels accompanied by absorption of photons.
Consider the excited state of the atom as an example of an atom of arsenic (As).Its valence is three.Interestingly, this value is true only in the case where the item is in a free state.Since the valence determined by the number of unpaired spins, upon receiving external energy atom at the site last seen steaming orbit with the transition of particles in the cell.As a result of changes orbit.Since the energy sublevels are simply reversed, the transition back (recombination), the ground state of the atom, is accompanied by the release of the equivalent of the energy absorbed in the form of photons.Returning to the example of arsenic: Due to changes in the number of unpaired spins in the excited state of the valence of the element corresponds to five.
schematically all of the above is as follows: the preparation of the atom from the outside portion of the external energy electrons are displaced a greater distance from the nucleus (radius orbits increases).However, because the protons in the nucleus is, the total value of the internal energy of the atom becomes larger.In the absence of a continuous supply of external energy electron very quickly returns to its previous orbit.Thus surplus of its energy is released in the form of electromagnetic radiation.
