atomic theory

n. The physical theory of the composition of matter stating that common materials are composed of molecules, which are composed of atoms, which are composed of nuclei and electrons. It holds that the properties of composite entities, such as their structure and behavior, arise from the properties of their components.

atomic theory

n 1. (Atomic Physics) any theory in which matter is regarded as consisting of atoms, esp that proposed by John Dalton postulating that elements are composed of atoms that can combine in definite proportions to form compounds 2. (Atomic Physics) the current concept of the atom as an entity with a definite structure. See atomic structure

Thesaurus

Noun	1.	atomic theory - a theory of the structure of the atomscientific theory - a theory that explains scientific observations; "scientific theories must be falsifiable"atomic physics, nuclear physics, nucleonics - the branch of physics that studies the internal structure of atomic nucleiBohr theory - (physics) a theory of atomic structure that combined Rutherford's model with the quantum theory; electrons orbiting a nucleus can only be in certain stationary energy states and light is emitted when electrons jump from one energy state to anotherRutherford atom - first modern concept of atomic structure; all of the positive charge and most of the mass of the atom are contained in a compact nucleus; a number of electrons (equal to the atomic number) occupy the rest of the volume of the atom and neutralize the positive charge
	2.	atomic theory - (chemistry) any theory in which all matter is composed of tiny discrete finite indivisible indestructible particles; "the ancient Greek philosophers Democritus and Epicurus held atomic theories of the universe"atomist theory, atomistic theory, atomismtheory - a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena; "theories can incorporate facts and laws and tested hypotheses"; "true in fact and theory"chemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions

atomic theory

1. any theory in which matter is regarded as consisting of atoms, esp that proposed by John Dalton postulating that elements are composed of atoms that can combine in definite proportions to form compounds 2. the current concept of the atom as an entity with a definite structure

Atomic theory

The study of the structure and properties of atoms based on quantum mechanics and the Schrödinger equation. These tools make it possible, in principle, to predict most properties of atomic systems. A stationary state of an atom is governed by a time-independent wave function which depends on the position coordinates of all the particles within the atom. To obtain the wave function, the time-independent Schrödinger equation, a second-order differential equation, has to be solved. The potential energy term in this equation contains the Coulomb interaction between all the particles in the atom, and in this way they are all coupled to each other. See Quantum mechanics

A many-particle system where the behavior of each particle at every instant depends on the positions of all the other particles cannot be solved directly. This is not a problem restricted to quantum mechanics. A classical system where the same problem arises is a solar system with several planets. In classical mechanics as well as in quantum mechanics, such a system has to be treated by approximate methods.

Independent particle model

As a first approximation, it is customary to simplify the interaction between the particles. In the independent particle model the electrons are assumed to move independently of each other in the average field generated by the nucleus and the other electrons. In this case the potential energy operator will be a sum over one-particle operators. The simplest wave function which will satisfy the resulting equation is a product of one-particle orbitals. To fulfill the Pauli exclusion principle, the total wave function must, however, be written in a form such that it will vanish if two particles are occupying the same quantum state. This is achieved with an antisymmetrized wave function, that is, a function which, if two electrons are interchanged, changes sign but in all other respects remains unaltered. The antisymmetrized product wave function is usually called a Slater determinant. See Exclusion principle

Hartree-Fock method

In the late 1920s, only a few years after the discovery of the Schrödinger equation, D. Hartree showed that the wave function to a good approximation could be written as a product of orbitals, and also developed a method to calculate the orbitals. Important contributions to the method were also made by V. Fock and J. C. Slater (thus, the Hartree-Fock method). The Hartree-Fock model thus gives the lowest-energy ground state within the assumption that the electrons move independently of each other in an average field from the nucleus and the other electrons.

To simplify the problem even further, it is common to add the requirement that the Hartree-Fock potential should be spherically symmetric. This leads to the central-field model and the so-called restricted Hartree-Fock method.

The Hartree-Fock method gives a qualitative understanding of many atomic properties. Generally it is, for example, able to predict the configurations occupied in the ground states of the elements. Electron binding energies are also given with reasonable accuracy.

Electron correlation

Correlation is commonly defined as the difference between the full many-body problem and the Hartree-Fock model. More specifically, the correlation energy is the difference between the experimental energy and the Hartree-Fock energy. There are several methods developed to account for electron correlation, including the configuration-interaction method, the multiconfiguration Hartree-Fock method, and perturation theory.

Strongly correlated systems

Although the Hartree-Fock model can qualitatively explain many atomic properties, there are systems and properties for which correlation is more important, such as negative ions, doubly-excited states, and some open-shell systems. If the interest is not in calculating the total energy of a state but in understanding some other properties, such as the hyperfine structure, effects beyond the central field model can be more important. See Hyperfine structure, Negative ion

Relativistic effects

The Schrödinger equation is a nonrelativistic wave equation. In heavy elements the kinetic energy of the electrons becomes very large, and calculations are based on the relativistic counterpart to the Schrödinger equation, the Dirac equation. It is possible to construct a Hartree-Fock model based on the Dirac equation, where the electron-electron interaction is given by the Coulomb interaction, a magnetic contribution, and a term which corrects for the finite speed (retardation) with which the interaction propagates. See Antimatter, Relativistic quantum theory

Radiative corrections

Radiative corrections, which arise when the electromagnetic field is quantized within the theory of quantum electrodynamics, For many-body systems, calculations of radiative effects are usually done within some independent-particle model, and the result is added to a correlated relativistic calculation based on the Dirac equation. See Atomic structure and spectra, Quantum electrodynamics

atomic theory

[ə′täm·ik ′thē·ə·rē] (chemistry) The assumption that matter is composed of particles called atoms and that these are the limit to which matter can be subdivided.

atomic theory

atomic theory

atomic theory

atomic theory

atomic theory

Atomic theory

Independent particle model

Hartree-Fock method

Electron correlation

Strongly correlated systems

Relativistic effects

Radiative corrections

atomic theory

atomic theory

a·tom·ic the·o·ry

atomic theory

atomic theory

Synonyms for atomic theory

noun a theory of the structure of the atom

Related Words

noun (chemistry) any theory in which all matter is composed of tiny discrete finite indivisible indestructible particles

Synonyms

Related Words