The atomic model is a model established by people's understanding of the microstructure of the material world.The generally accepted atomic model isNucleus（protonandneutron）AndElectronicsFormed by the irregular movement of electrons around the nucleusElectronic cloud model。The atomic model was first proposed by Dalton, a British scientist, in 1803. Through the improvement and perfection of Thomson, Rutherford, Bohr and others, the modern atomic model was formed.
The history of human understanding of the atom is long and endless.The atomic structure model is a vivid description of the atomic structure by scientists according to their own knowledge. A model represents a stage of human understanding of atomic structure.[1]The atomic model mainly includes Dalton atomic model, Thomson atomic model, Rutherford's nuclear atomic model andBohr Atomic Model And other important stages, which concisely and vividly show the gradual deepening of human understanding of atomic structure.
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Dalton atomic model
With the accumulation of experience and knowledge and the deepening understanding of the objective world,Dalton(Dalton, UK) The atomic theory proposed in 1803 is essentially different from the ancient atomic theory. The main points of Dalton's atomic theory are as follows:[2]
(1) Atoms are the smallest and indivisible solid spheres. The atoms of the same element are the same, such as volume, mass and chemical properties, but the atoms of different elements are different;
(2) A compound is composed of atoms of two or more elements. In a compound, the ratio of the atomic numbers of any two elements is either an integer or a simple fraction;
(3) Chemical reaction is the separation and combination of different atoms, without the creation or disappearance of atoms.
Doyle's atomic theory can not only fully explain the existing basic laws of chemistry (such as the law of conservation of mass, the law of equivalence, etc.), but also mutually confirm with experimental facts, so that the theory has removed the philosophical veil and really become a scientific concept. The establishment of Dalton's atomic theory marks a major step forward in human understanding of the structure of matterThe development of chemistry and biology laid an important theoretical foundation, especially opened the gate for the surging and rapid development of chemistry. On the other hand, due to the limitations of the scientific level and experimental conditions at that time, the idea of the indivisibility of atoms hindered the further development of the theory of material structure for a long time.
Thomson atomic model
Figure 1
In 1890, it was found that under the action of high voltage, the cathode of the cathode ray tube would emit an invisible ray, which would move to the anode. However, if a layer of zinc sulfide was coated on the surface of the glass ray tube, the cathode ray would show up in the form of green fluorescence, and it was further found through the experiment of the interaction between the ray and the magnetic field,This kind of ray is composed of a stream of negatively charged particles, as shown in Figure 1. People call this negatively charged particle electron. By the beginning of the 20th century, a large number of accumulated experimental results showed that all atoms contain electrons, followed by the discovery of X-ray and radioactive decay.All kinds of signs show that atoms are not indivisible. Atoms contain both negatively charged electrons and positively charged nuclei, and atoms can also change.Further from the measurement results of the charge mass ratio of the electron (i.e. the ratio of the electric quantity carried to its mass e/m), it is found that the mass of the electron is far less than the mass of the whole atom. On this basis,Thomson (Thomson, UK) proposed a new atomic model in 1904, that is, the atom is a spherical jelly like particle, in which a certain number of positive charges are evenly distributed, and a certain number of electrons are embedded on the spherical jelly like particle, but the atom as a whole is electrically neutral, and the number of positive charges and negative charges contained in it is equal.
Rutherford's Nucleogen Model
Figure 2
At the beginning of the 20th century, physicistsrutherford(Rutherford, UK) et al. have conducted multiple scattering experiments of alpha particles (i.e. helium nuclei He), as shown in Figure 2.The result is that when alpha particles are scattered by the platinum film, most of the scattering angles are between 2 ° and 3 °, but about 1/8000 alpha particles have scattering angles greater than 90 °, among which some are close to 180 °. This experimental result cannot be explained by Thomson atomic model. Therefore, Rutherford put forward the nuclear atom model in 1911. He believed that there is a positiveA very small nucleus with almost all the atomic mass concentrated.Outside the nucleus, there are electrons with the same number of positive charges as the nucleus. These electrons rotate around the nucleus at a high speed.The diameter of the nucleus is about 10-15~10-14M, while the atomic diameter is usually about 10-10m。
Bohr atomic model
Figure 3
Rutherford's nuclear atom model is simple and easy to understand, but it can't explain the linear hydrogen spectrum discovered soon afterwards. We know that when sunlight passes through a prism, it will get a rainbow like color band.As the color of the transmitted light changes in the order of red, orange, yellow, green, cyan, blue, and purple, its wavelength changes continuously, that is, the continuous spectrum is obtained. We call this continuous spectrum band spectrum.In sharp contrast, if a sealed glass tube is filled with thin hydrogen gas and makes it glow, this light will be decomposed by a prism to obtain a group of linear light with different wavelengths.This group of linear spectra is composed of light rays whose wavelengths are determined, rather than band spectra whose wavelengths change continuously, as shown in Figure 3.
According to the classical electromagnetic theory, when the electron rotates around the atomic nucleus, it will inevitably emit electromagnetic waves. At the same time, the energy of the electron will gradually decrease, and eventually the electron will fall on the atomic nucleus. At this time, the atom will be destroyed. This conclusion obtained from the analysis of the classical electromagnetic theory is obviously inconsistent with the fact, the fundamental reason is that Rutherford's model of nuclear atoms still has shortcomings,In order to illustrate the experimental results of hydrogen atomic spectrum, Bohr (Denmark) proposed in 1913, combining the existing experimental results and quoting Planck's quantum theory that the microscopic particles can not absorb or emit energy in the form of continuous electromagnetic waves, but can only absorb or emit energy discontinuously, one by oneBohr atomic modelThe key points of Bohr atomic model are as follows:
(1) The extranuclear electrons can only move in some specific circular orbits with a certain energy, and this movement does not absorb or release energy, that is, the energy of the atom does not change during the electronic movement.This state of motion is called stationary state. Electrons moving in different orbits are in different stationary states.
(2) When the electron moves in the orbit closest to the nucleus, the energy of the electron is the lowest. This stationary state is called the ground state. Generally, all atoms are in the ground state. When the energy is supplied from the outside, the electrons in the ground state may absorb energy and be excited to jump to the orbit far away from the nucleus with higher energy,The stationary state with high energy is called excited state.
(3) When electrons transition between different stationary states, they will be absorbed or released with energy.If energy is absorbed or released in the form of electromagnetic wave, the relationship between the frequency v of electromagnetic wave and the energy difference △ E between two stationary states is as follows:
ΔE=|
-
|=hν
Where, h=6.626 × 10-34J ▪ s, h is Planck constant.
Since the energies E1, E2,... of different stationary states (i.e. different energy levels) are discrete and discontinuous, the frequency (or wavelength) of the absorption or emission spectrum is also discrete and discontinuous, and its spectrum is linear.
Although the Bohr atomic model can explain the simpleAtomic hydrogen spectroscopyBut this is only one side of its success.In fact, when using an instrument with high resolution, each hydrogen atom spectral line shown in Figure 3 above is composed of several spectral lines with very close wavelengths. The Bohr atomic model cannot explain the fine structure of this hydrogen atom spectrum, nor can it explain the multi electron atomic spectrum, which indicates that the Bohr atomic model also has its shortcomings.Although, for example, Bohr theory is the first time to incorporate spectral experimental facts into a theoretical system and propose a dynamic atomic structure wheel seat based on the nuclear atom model.The theory pointed out that classical physics could not be fully applied to microscopic particles, and proposed the unique quantum laws of microscopic particle movement, which opened up a new way for the development of atomic physics at that time
