Atomic theory

An atomic model is an idea of ​​the atoms, which were regarded as the immutable basic building blocks of all material substances according to the atomic hypothesis of antiquity. The first atomic hypothesis could only be based on the philosophical preference for a particle model against the hypothesis of infinitely continuable divisibility of matter. The different properties of the material substances should be attributed to the possible combinations of a few kinds of atoms. It was not until the early 19th century showed itself in the chemistry and physics scientific evidence of the real existence of atoms: the atom was defined as the smallest unit of a chemical element, and the behavior of gases could according to the kinetic theory of gases completely out of the disorderly movement a plurality of identical molecules, each consisting of a few atoms, will be explained. As a model of the atom in this case was sufficient the idea of ​​a small ball of about 0.1 nm in diameter and 10-26 kg mass. In this form, the end of the 19th century, the atomic theory had largely prevailed, showed as new observations with electron beams or radioactive substances, that these atoms themselves consist of smaller particles. The explanation of their complicated internal structure led in 1925 to quantum mechanics, the atomic models are primarily formulated as mathematical statements. On the question of how you have an atom have now imagine, replied Werner Heisenberg, one of the creators of quantum mechanics: " Try not even going! "

The following chronological list gives an overview. Important models have main article. Currently common are also shown in the article atom in context.

  • The particle model of Democritus ( about 400 BC) postulated the existence of different types of solid, indivisible particles, which combines different form the known substances.
  • The Dalton model ( 1803) is based on the smallest, indivisible particles, which differ depending on the element in their mass, in particular number ratios are (depending on the type of substance ) linked to each other and just rearrange during chemical reactions.
  • In Dynamidenmodell (1903 ) by Philipp Lenard atoms consist mostly of empty space between small, rotating electric dipoles, the Dynamides.
  • After thomson Atomic Energy Model (1903 ) is the atom of a uniformly distributed positive charge, and negatively charged electrons that move in it. This model is also called plum pudding model or German raisin cake model.
  • In the planetary model or Saturn model of Nagaoka Hantaro (1904 ), the atom is a positively charged sphere, surrounded by negatively charged electrons. In analogy to the stability of the rings of Saturn, the model predicts correctly a very massive core, but also a wrong energy dissipation due to the motion of the electrons.
  • After rutherford Atomic Energy Model (1911 ) is the atom of a positively charged nucleus, which contains nearly the entire mass of the atom, and an atomic shell of electrons.
  • According to the Bohr model of the atom (1913 ), the atom consists of a positively charged, mass -bearing core and electrons orbiting those on certain tracks, without emitting energy.
  • The bohr - Sommerfeld atomic model (1916 ) is an extension of the Bohr model of the atom, in which certain elliptical orbits are allowed around the nucleus.
  • The shell model ( atomic physics ) simplifies the atom so that a positively charged nucleus surrounded by spherical shells in which the electrons are. Only the outermost shell is responsible for chemical properties of the element. Via the movement of electrons no statement is made.
  • The spherical cloud model ( kimballsches atomic model, tetrahedron model) is a commonly used in school atom model, which is an extension of the shell model.
  • After the orbital model (1928) the atom consists of a core which is surrounded by electrons in orbitals. The shape of the orbital is given by the spatial probability of the electrons. In the strict sense, an orbital is a stationary solution of the quantum mechanical Schrödinger equation ( an energy state of an electron ).
  • In the Thomas-Fermi model (1928), the electron cloud will be described collectively as a Fermi - gas is trapped in the potential well resulting from the Coulombic attraction through the core.
  • In some areas, atoms can still be approximated as points without extension, in the kinetic theory of gases as the model of an ideal gas, as in other spheres with fixed volume, such as the van der Waals gas. The corresponding model is also called point particle model and incompressible spheres model.

Models of the atomic nucleus

  • The droplet model (1936 ) describes the atomic nucleus as droplets of an electrically charged liquid.
  • The shell model (1949 ) describes the atomic nucleus, in close analogy to the orbital model of the atomic shell.