The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The invention of the periodic system of elements by Dmitri Mendeleev was another great step forward. At this stage, it wasn't clear what atoms were, although they could be described and classified by their properties (in bulk). This theory was later developed in the modern sense of the basic unit of a chemical element by the British chemist and physicist John Dalton in the 18th century. It forms a part of the texts written in 6th century BC to 2nd century BC, such as those of Democritus or Vaiśeṣika Sūtra written by Kaṇāda. One of the earliest steps towards atomic physics was the recognition that matter was composed There are rather strict selection rules as to the electronic configurations that can be reached by excitation by light - however, there are no such rules for excitation by collision processes. The Auger effect allows one to multiply ionize an atom with a single photon. In this case, a visible photon or a characteristic X-ray is emitted, or a phenomenon known as the Auger effect may take place, where the released energy is transferred to another bound electron, causing it to go into the continuum. If an inner electron has absorbed more than the binding energy (so that the atom ionizes), then a more outer electron may undergo a transition to fill the inner orbital. In a neutral atom, the system will emit a photon of the difference in energy, since energy is conserved. After a certain time, the electron in an excited state will "jump" (undergo a transition) to a lower state. If the electron absorbs a quantity of energy less than the binding energy, it will be transferred to an excited state. The atom is said to have undergone the process of ionization. Any quantity of energy absorbed by the electron in excess of this amount is converted to kinetic energy according to the conservation of energy. The energy necessary to remove an electron from its shell (taking it to infinity) is called the binding energy. An electron from shell (n=2) must have been removed beforehand by ionizationĮlectrons that populate a shell are said to be in a bound state. In the Bohr model, the transition of an electron with n=3 to the shell n=2 is shown, where a photon is emitted. These are normally in a ground state but can be excited by the absorption of energy from light ( photons), magnetic fields, or interaction with a colliding particle (typically ions or other electrons). By this consideration, atomic physics provides the underlying theory in plasma physics and atmospheric physics, even though both deal with very large numbers of atoms.Įlectrons form notional shells around the nucleus. This means that the individual atoms can be treated as if each were in isolation, as the vast majority of the time they are. While modelling atoms in isolation may not seem realistic, if one considers atoms in a gas or plasma then the time-scales for atom-atom interactions are huge in comparison to the atomic processes that are generally considered. It is concerned with processes such as ionization and excitation by photons or collisions with atomic particles. It is not concerned with the formation of molecules (although much of the physics is identical), nor does it examine atoms in a solid state as condensed matter. Atomic models will consist of a single nucleus that may be surrounded by one or more bound electrons. Physics research groups are usually so classified.Ītomic physics primarily considers atoms in isolation. Physicists distinguish between atomic physics-which deals with the atom as a system consisting of a nucleus and electrons-and nuclear physics, which studies nuclear reactions and special properties of atomic nuclei.Īs with many scientific fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of atomic, molecular, and optical physics. The term atomic physics can be associated with nuclear power and nuclear weapons, due to the synonymous use of atomic and nuclear in standard English. This comprises ions, neutral atoms and, unless otherwise stated, it can be assumed that the term atom includes ions. The processes by which these arrangements change. It is primarily concerned with the way in which electrons are arranged around the nucleus and Atomic physics typically refers to the study of atomic structure and the interaction between atoms. Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus.
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