The perception of an atom as the least indivisible particle of substance was the foundation of the cinematic gas theory. It have explained and predicted a series of the experimental phenomena. However, at the end of XIX century new experimental data proved the composite structure of an atom. The experimentally found laws of radiation and uptake of energy by atoms (spectral series, radiation of an ideal black body, photoeffect) have not received an explanation within the framework of a classical electrodynamics. Only new ideas, based on the quantum theory, helped explaining these phenomenon.
Structure of atom.
British physicist Ernest Rutherford (1871-1937) has created a planetary model of atom exploring a dispersion of a-particles transiting through a thin metal foil. According to this model an atom looks like a tiny planetary system, in which the forces of an electrical attraction operate.
The center of an atom is a positively charged kern. Almost all mass of an atom is focused there. Negatively charged eletrons rotate around the kern.
An atom of hydrogen has the most simple structure. Positively charged kern of an atom of hydrogen was called a proton. The only electron rotates around it. It was determined later, that every atom's kern consists of protons and neutrons. The neutron's mass is almost equal to proton's, but has not electric charge.
The mass of an electron is about 1/1840 of a proton's mass and does not influence an atomic weight of substance. The number of positive and negative charges of atom determines the position of a suvstance in a periodic system. The positive charge of an atom's kern is equal to a serial number of a substance in the table. The number of neutrons in an atom's kern is equal to a residual between a rounded atomic weight and a number of positive protons in a kern (serial number of substance). The electrical neutrality rule of atom says, that the number of electrons rotating around the kern is equal to a number of positive protons contained in an atom.
Parameters of atom.
According to the Rutherford's experimental results the radius of a trajectory of an electron in a hydrogen atom is 0,53 x 10-10 m, the diameter of an atom of hydrogen is equal to 2,6 x 10-15 m. Volume of electrons and kern is approximately 1/10 000 of an atom's volume. The substance of a kern has huge density of 200 million tonn in 1 cm3. It is all because the most of an atom's mass is consentrated in its kern. The mass of a positive proton is approximately equal to the mass of a neutron and is 1,67 x 10-27. The mass of an electron is 9,11 x 10-31 kgs.
The classic radius of an electron, r0 , is equal to 2,8 x 10-17 m. It is the distance, on which the electrostatic energy of an electron intercoursing with a point charge of the same quantity is equal to natural energy of an electron:
|e - elementary charge; c - speed of light in vacuo;
m0 - electronic mass
Deficiencies of the theory.
The Rutherford model of atom was well correlated with the results of a dispersion of an a-particle by atoms of substance, but it has not explained neither the process of radiation of atoms, nor legitimacies in spectrums of radiation. According to the laws of an electrodynamics rotating around the kern the electron should radiate electromagnetic waves. As a result of radiation the natural energy of an electron should be diminished, thus the trajectory it will be figured by a spiral, and during the order 10-8 about an electron should fall on a kern. Such deduction obtained on the basis of representations of classical physics about radiation, contradicted known stability of atoms and character of nuclear spectrums of radiation.